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Last Updated :2024/08/27

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Master

Affiliation (Master)

  • Faculty of Fisheries Sciences　Marine Life Science　Aquaculture Genetics and Genomics

Affiliation (Master)

  • Faculty of Fisheries Sciences　Marine Life Science　Aquaculture Genetics and Genomics

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Profile and Settings

Profile and Settings

  • Name (Japanese)

    Mizuta

  • Name (Kana)

    Hiroyuki

  • Name

    201301026266335601

Achievement

Research Interests

  • 生活環制御   防御応答   栄養塩   コンブ類   成熟   子嚢斑   培養   環境要因   植物成長調整物質   再分化   植物生長調整物質   抵抗性   組織培養   種苗   光質   活性酸素   マコンブ   ヨウ素   増殖   繁殖   生態系モデル   基礎生産   スサビノリ   

Research Areas

  • Life sciences / Aquaculture
  • Life sciences / Marine/Aquatic life sciences

Research Experience

  • 2013 - Today 北海道大学 水産科学研究研究院 教授

Published Papers

  • Toshiki Uji, Takuya Kandori, Hiroyuki Mizuta
    Frontiers in Plant Science 15 2024/08/06 [Refereed]
     
    Saccharina japonica, a significant brown macroalga in the Pacific Ocean, serves as a food source and industrial material. In aquaculture, collecting mature sporophytes for seedling production is essential but challenging due to environmental changes. In this study, transcriptomic analysis of vegetative and sorus tissues was done to identify differentially expressed genes (DEGs) and enhance our understanding of sorus formation regulation in S. japonica. KEGG pathway and Gene Otology (GO) analysis revealed that upregulated DEGs were involved in folate biosynthesis, riboflavin metabolism, and amino acid biosynthesis. In addition, the upregulation of genes associated with cell wall remodeling, such as mannuronan C-5-epimerases, vanadium-dependent haloperoxidases, and NADPH oxidase, was observed in sorus parts. Meanwhile, downregulated DEGs in sorus portions included genes related to chloroplast function. These findings will help us understand the regulatory mechanisms behind sorus formation in S. japonica and extracellular matrix remodeling in brown algae.
  • Shoichi Akaike, Hiroyuki Mizuta
    European Journal of Phycology 59 (2) 218 - 231 0967-0262 2024/02/27 [Refereed]
  • Kenshiro ABE, Inori ARIGA, Toshiki UJI, Hiroyuki MIZUTA
    Cahiers de Biologie Marine 65 73 - 85 2024/01 [Refereed]
  • Shinnosuke Ueda, Hiroyuki Mizuta, Toshiki Uji
    MOLECULAR BIOTECHNOLOGY 1073-6085 2022/09 [Refereed]
     
    Epigenetic regulation by histone modification can activate or repress transcription through changes in chromatin dynamics and regulates development and the response to environmental signals in both animals and plants. Chromatin immunoprecipitation (ChIP) is an indispensable tool to identify histones with specific post-translational modifications. The lack of a ChIP technique for macroalgae has hindered understanding of the role of histone modification in the expression of genes in this organism. In this study, a ChIP method with several modifications, based on existing protocols for plant cells, has been developed for the red macroalga, Neopyropia yezoensis, that consists of a heterogeneous alternation of macroscopic leaf-like gametophytes and microscopic filamentous sporophytes. ChIP method coupled with qPCR enables the identification of a histone mark in generation-specific genes from N. yezoensis. The results indicate that acetylation of histone H3 at lysine 9 in the 5 ' flanking and coding regions from generation-specific genes was maintained at relatively high levels, even in generation-repressed gene expression. The use of this ChIP method will contribute significantly to identify the epigenetic regulatory mechanisms through histone modifications that control a variety of biological processes in red macroalgae.
  • Toshiki Uji, Hiroyuki Mizuta
    JOURNAL OF APPLIED PHYCOLOGY 34 (3) 1527 - 1536 0921-8971 2022/06 [Refereed]
     
    Heat stress disrupts algal growth, development, and physiological processes, such as photosynthesis, and eventually decreases seaweed productivity. Previous studies of crop plants have revealed that exogenous application of phytohormones prior or parallel to stress can alleviate the negative effects of abiotic stressors, including heat stress. However, there is limited information on phytohormone-induced tolerance to abiotic stressors in seaweed. In the present study, the application of the major plant hormones abscisic acid and salicylic acid failed to mitigate the negative effects of heat stress on the marine red alga Neopyropia yezoensis, whereas 1-aminocyclopropane-1-carboxylic acid (ACC), the direct precursor of the plant hormone ethylene, regulates thermotolerance. In addition, the ACC analogs 1-aminocyclobutane-1-carboxylic acid and alpha-aminoisobutyric acid enhanced tolerance to heat stress. ACC increased the expression of genes involved in antioxidant defense systems to protect photosynthesis and respiration. These results suggest ACC acts as a phytohormone to mitigate the impact on heat stress independent of ethylene in N. yezoensis.
  • Sayaka Kominami, Hiroyuki Mizuta, Toshiki Uji
    MARINE BIOTECHNOLOGY 24 (2) 393 - 407 1436-2228 2022/04 [Refereed]
     
    Many organisms are subjected to a daily cycle of light and darkness, which significantly influences metabolic and physiological processes. In the present study, Neopyropia yezoensis, one of the major cultivated seaweeds used in "nori," was harvested in the morning and evening during light/dark treatments to investigate daily changes in gene expression using RNA-sequencing. A high abundance of transcripts in the morning includes the genes associated with carbon-nitrogen assimilations, polyunsaturated fatty acid, and starch synthesis. In contrast, the upregulation of a subset of the genes associated with the pentose phosphate pathway, cell cycle, and DNA replication at evening is necessary for the tight control of light-sensitive processes, such as DNA replication. Additionally, a high abundance of transcripts at dusk encoding asparaginase and glutamate dehydrogenase imply that regulation of asparagine catabolism and tricarboxylic acid cycle possibly contributes to supply nitrogen and carbon, respectively, for growth during the dark. In addition, genes encoding cryptochrome/photolyase family and histone modification proteins were identified as potential key players for regulating diurnal rhythmic genes.
  • Toshiki Uji, Takuya Kandori, Shiho Konishi, Hiroyuki Mizuta
    BMC PLANT BIOLOGY 22 (1) 1471-2229 2022/04 [Refereed]
     
    Background 1-aminocyclopropane 1-carboxylic acid (ACC) is the immediate precursor of the plant hormone ethylene. However, recent studies have suggested that ACC also acts as a signaling molecule to regulate development and growth independently from ethylene biosynthesis. In red algae, ACC stimulates the switch from a vegetative to a sexual reproductive phase. However, despite evidence that ACC signaling in plants and algae is widespread, the mechanistic basis of the ACC signaling pathway remains unknown. Results We demonstrate that exogenous ACC increased the activity of phospholipase D (PLD) and induced the accumulation of PLD transcripts in the marine red alga Neopyropia yezoensis. The product of PLD, the lipid second messenger phosphatidic acid (PA), also increased in response to ACC. Furthermore, the pharmacological inhibition of PLD by 1-butanol blocked ACC-induced spermatangia and carpospore production, but the inactive isomer t-butanol did not. In addition, 1-butanol prevented ACC-induced growth inhibition and inhibited transcript accumulation of genes upregulated by ACC, including extracellular matrix (ECM)-related genes, and alleviated the transcriptional decrease of genes downregulated by ACC, including photosynthesis-related genes. Conclusions These results indicate that PLD is a positive regulator of sexual cell differentiation and a negative regulator of growth. This study demonstrates that PLD and its product, PA, are components of ACC signaling during sexual reproduction in N. yezoensis.
  • Toshiki Uji, Shinnosuke Ueda, Hiroyuki Mizuta
    Phycology MDPI AG 2 (1) 45 - 59 2022/01/06 [Refereed]
     
    Extracellular matrix (ECM) proteins play crucial roles in the regulation of cell proliferation and differentiation. We identified homologous genes encoding ECM proteins that are known to associate with integrins in animal cells in red macroalga Neopyropia yezoensis. Four genes encoding spondin domain-containing proteins (NySPLs) and eight genes encoding fasciclin domain-containing proteins (NyFALs) from N. yezoensis were selected for bioinformatics and expression analysis in order to obtain insights into the roles of ECM proteins for the life cycle. NySPLs had eight β-strands with two contiguous α-helices, which were similar to those of the F-spondin domain of animals. NyFALs had conserved H1 and H2 motifs and a YH motif between the H1 and H2 regions. Quantitative reverse transcription polymerase chain reaction showed that NySPL1–3 and NyFAL8 transcripts were highly accumulated in mature gametophytes that formed the spermatia. Furthermore, expressions of all NySPLs were upregulated in response to the ethylene precursor 1-aminocylopropane-1-carboxylic acid that induces gametogenesis. NyFAL1, 4 were highly expressed in sporophytes, whereas NyFAL2, 3, 5, 6, and 7 were overexpressed in gametophytes, especially at the vegetative stage. These findings facilitate future research on ECM architecture in the unique life cycles of red macroalgae.
  • Toshiki Uji, Hiroyuki Mizuta
    Frontiers in plant science 13 1019334 - 1019334 2022 [Refereed]
     
    Seaweeds or macroalgae are important primary producers that serve as a habitat for functioning ecosystems. A sustainable production of macroalgae has been maintained by a diverse range of life cycles. Reproduction is the most dynamic change to occur during its life cycle, and it is a key developmental event to ensure the species' survival. There is gradually accumulating evidence that plant hormones, such as abscisic acid and auxin, have a role on the sporogenesis of brown alga (Saccharina japonica). Recent studies reported that 1-aminocylopropane-1-carboxylic acid, an ethylene precursor, regulates sexual reproduction in red alga (Neopyropia yezoensis) independently from ethylene. In addition, these macroalgae have an enhanced tolerance against abiotic and biotic stresses during reproduction to protect their gametes and spores. Herein, we reviewed the current understanding on the regulatory mechanisms of red and brown algae on their transition from vegetative to reproductive phase.
  • Toshiki Uji, Hiroyuki Mizuta
    AQUACULTURE RESEARCH 52 (12) 6814 - 6817 1355-557X 2021/08 [Refereed]
  • Extracellular silicate uptake and deposition induced by oxidative burst in Saccharina japonica sporophytes (Phaeophyceae)
    Hiroyuki Mizuta, Toshiki Uji, Hajime Yasui
    Algal Research 58 102369  2021/06/07 [Refereed][Not invited]
  • α-aminoisobutyric acid mimics the effect of 1-aminocyclopropane-1-carboxylic acid to promote sexual reproduction in the marine red alga Pyropia yezoensis (Rhodophyta)
    Harune Endo, Hiroyuki Mizuta, Toshiki Uji
    Jounarl of applied phycology 33 1081 - 1087 2021/01/02 [Refereed][Not invited]
  • Sexual Reproduction via a 1-Aminocyclopropane-1-Carboxylic Acid-Dependent Pathway Through Redox Modulation in the Marine Red Alga Pyropia yezoensis (Rhodophyta)
    Toshiki Uji, Harune Endo, Hiroyuki Mizuta
    Frontiers in plant science 11 60  2020/02/12 [Refereed]
  • Ryo Yanagisawa, Naoki Sekine, Hiroyuki Mizuta, Toshiki Uji
    JOURNAL OF APPLIED PHYCOLOGY 31 (5) 3317 - 3329 0921-8971 2019/10 [Refereed][Not invited]
     
    The marine red algal genus Pyropia, class Bangiophyceae, includes dioecious and monoecious species; however, the molecular mechanisms underlying control of their sexual reproduction are still poorly understood. In the present study, we demonstrated that application of the ethylene precursor, 1-aminocyclopropane-1-carboxylic acid (ACC), promoted the formation of spermatangia and parthenosporangia in male and female gametophytes, respectively, of the dioecious species Pyropia pseudolinearis. In addition, we determined expression profiles of ACC-responsive genes in the gametophytes during sexual reproduction using RNA-Seq and quantitative real-time PCR (qRT-PCR). Genes involved in the regulation of cell division and cell wall organization, such as high-mobility group (PpHMG) and glycosyltransferase family (PpGT14), were found to be upregulated in male and female gametophytes treated with ACC. In addition, the relatively rapid ACC-response of the vesicular-trafficking-related genes, flotillin (PpFLOT), charged multivesicular body protein 5 (PpCHMP5), and peptidase family S8 (PpS8) was shown to occur during male and female sexual reproduction. Expression levels of these six genes in the monoecious species P. yezoensis, which are homologs to ACC-responsive genes in P. pseudolinearis, also increased in gametophytes treated with ACC. These findings could provide new insights into the ACC-regulation of the sexual life cycle in Pyropia species.
  • Characterization and expression profiles of small heat shock proteins in the marine red alga Pyropia yezoensis
    T. Uji, Y. Gondaira, S. Fukuda, H. Mizuta, N. Saga
    Cell Stress and Chaperones 24 223 - 233 2019/01/10 [Refereed]
  • Shimizu K, Uji T, Yasui H, Mizuta H
    Journal of Applied Phycology 30 (2) 1371 - 1379 0921-8971 2018 [Refereed][Not invited]
     
    In this study, the oligoguluronate elicitor-induced oxidative burst (OB) was monitored continuously in young and mature Saccharina japonica sporophytes based on luminol chemiluminescence using a photon counter. The iodoperoxidase (IPO) activity, abscisic acid (ABA), and polyphenol contents were also compared in the different growth stages. The elicitor-induced OB occurred within 1 min and reached its maximum in 15-20 min after treatment in all growth stages. The active elicitor-induced OB was stronger in the young sporophytes than the older sporophytes. The IPO activity in the different growth stages also exhibited a similar pattern to the elicitor-induced OB. These results suggest that the elicitor-induced OB and the subsequent high haloperoxidase activity comprise a major defence mechanism in young sporophytes. By contrast, ABA accumulated with the growth of the sporophytes. Interestingly, ABA treatment suppressed the elicitor-induced OB during growth and enhanced the elicitor-independent IPO activity even in the young sporophytes. In addition, the polyphenol content was higher in the older sporophytes than the younger sporophytes. These observations show that dramatic changes occur in the characteristic defences against biotic stresses as the sporophyte grows, as well as suggesting that ABA is closely linked with these changes. Moreover, the IPO activity recovered slightly in the sorus, which is the reproductive tissue, thereby suggesting that a higher ABA content increases the defence activity and the success of reproduction.
  • Toshiki Uji, Ryuya Matsuda, Katsuaki Takechi, Hiroyoshi Takano, Hiroyuki Mizuta, Susumu Takio
    JOURNAL OF APPLIED PHYCOLOGY 28 (6) 3501 - 3509 0921-8971 2016/12 [Refereed][Not invited]
     
    Plant growth regulators (PGRs) play a pivotal role in vascular plants, regulating growth, development, and stress responses; however, the role of PGRs in algae remains largely unexplored. Here, the role of ethylene, a simple plant growth regulator, was demonstrated in sexual reproduction of the marine red alga Pyropia yezoensis. Application of the ethylene precursor 1-aminocylopropane-1-carboxylic acid (ACC) promoted the formation of spermatia and zygotospores in the gametophytes as well as ethylene production, whereas the growth rate was repressed in comparison to gametophytes not treated with ACC. In addition, gametophytes treated with ACC and mature gametophytes showed enhanced tolerance to oxidative stress. Gene expression profiles revealed upregulation of genes involved in cell division and stress response in gametophytes treated with ACC and in mature gametophytes. These results indicate that ethylene plays an important role in the regulation of gamete formation and protection against stress-induced damage during the sexual reproductive stage. Considered together, these findings demonstrate that ethylene is involved in regulating the switching from a vegetative to a sexual reproductive phase in P. yezoensis.
  • Tani Takashi, Kawagoe Chikara, Matsumoto Setsuko, Mizuta Hiroyuki, Yasui Hajime
    Aquaculture Science 日本水産増殖学会 63 (3) 235 - 244 0371-4217 2015 [Refereed][Not invited]
     
    Seasonal variations and accompanying morphological changes of 'Gagome-kombu' (Saccharina sculpera) from Hakodate, Hokkaido Prefecture were observed for three years. The growth, maturation and renewal of first-year, second-year and third-year plants were documented. Between January and July, first-year plants with frond lengths less than 5 cm emerged and grew slowly to 10 cm by October. Although renewal was observed in first-year plants during October and January, no mature plants were observed. Second-year plants grew between January and July into large plants over 2 m in length, withered between August and October and reached maturity between October and November. Although renewal into third-year plants were observed in about 40% of 400 second-year plants, most of these plants withered and died by April of the third-year. Only 2% of the second-year plants continued to grow until July, withering between August and October and maturing in October and November. All the plants withered and died by December of the third-year.
  • Ryo Hirata, Toshiki Uji, Satoru Fukuda, Hiroyuki Mizuta, Asao Fujiyama, Satoshi Tabata, Naotsune Saga
    JOURNAL OF APPLIED PHYCOLOGY 26 (4) 1863 - 1868 0921-8971 2014/08 [Refereed][Not invited]
     
    Genetic transformation systems using reporter genes in whole plants have a wide variety of applications for molecular biological study including the visualization of expression patterns of particular genes and intracellular biological phenomena as well as the identification of novel genes. In this study, we assessed co-expression of each three codon-optimized reporter genes and a selectable marker in the nuclear transformation system of whole Pyropia yezoensis, a red marine alga. With the use of an endogenous promoter, both the codon-optimized hygromycin resistance gene and -glucuronidase gene (PyGUS) were co-expressed in P. yezoensis cells. A high level of GUS activity was observed in 60 % of the individuals in hygromycin-resistant lines. A histochemical GUS assay revealed that the PyGUS reporter gene was stably introduced and expressed throughout the algae's life cycle. In addition, two live cell reporters, humanized cyan fluorescent protein from Anemonia majano and luciferase from Gaussia princeps, were successfully expressed in whole P. yezoensis. The development of this transformation system involving three types of reporter genes provides opportunities for monitoring temporal changes in gene expression and for genetic screening in red marine algae.
  • Toshiki Uji, Ryo Hirata, Satoru Fukuda, Hiroyuki Mizuta, Naotsune Saga
    MARINE BIOTECHNOLOGY 16 (3) 251 - 255 1436-2228 2014/06 [Refereed][Not invited]
     
    Marine macroalgae play an important role in marine coastal ecosystems and are widely used as sea vegetation foodstuffs and for industrial purposes. Therefore, there have been increased demands for useful species and varieties of these macroalgae. However, genetic transformation in macroalgae has not yet been established. We have developed a dominant selection marker for stable nuclear transformation in the red macroalga Pyropia yezoensis. We engineered the coding region of the aminoglycoside phosphotransferase gene aph7aEuro(3) from Streptomyces hygroscopicus to adapt codon usage of the nuclear genes of P. yezoensis. We designated this codon-optimized aph7aEuro(3) gene as PyAph7. After bombarding P. yezoensis cells with plasmids containing PyAph7 under the control of their endogenous promoter, 1.9 thalli (or individuals) of hygromycin-resistant strains were isolated from a 10-mm square piece of the bombarded thallus. These transformants were stably maintained throughout the asexual life cycle. Stable expression of PyAph7was verified using Southern blot analysis and genomic PCR and RT-PCR analyses. PyAph7 proved to be a new versatile tool for stable nuclear transformation in P. yezoensis.
  • Toshiki Uji, Rei Sato, Hiroyuki Mizuta, Naotsune Saga
    JOURNAL OF APPLIED PHYCOLOGY 25 (6) 1887 - 1893 0921-8971 2013/12 [Refereed][Not invited]
     
    Multiprotein bridging factor 1 (MBF1) is a highly conserved transcriptional co-activator involved in the regulation of diverse processes, such as environmental stress responses. We recently identified a novel MBF1 gene, PyMBF1, from the marine red alga Pyropia yezoensis. In this study, quantitative real-time PCR analysis revealed that PyMBF1 transcripts were upregulated in P. yezoensis cells during exposure to oxidative and heat stresses. We also examined heat signaling in P. yezoensis cells by monitoring the accumulation of PyMBF1 transcripts. Heat activation of PyMBF1 was inhibited by the membrane rigidifier dimethylsulfoxide, whereas it was induced without heat stress by the membrane fluidizer benzyl alcohol (BA). Induction of PyMBF1 transcripts by heat and BA was inhibited by 1-butanol, an inhibitor of phospholipase D (PLD). The results suggest that the heat activation of PyMBF1 requires membrane fluidization and activation of PLD. These findings provide an initial step toward understanding heat signaling in marine red algae.
  • Yang Liu, Sei-Ichi Saitoh, I. Nyoman Radiarta, Tomonori Isada, Toru Hirawake, Hiroyuki Mizuta, Hajime Yasui
    ICES JOURNAL OF MARINE SCIENCE 70 (7) 1460 - 1470 1054-3139 2013/11 [Refereed][Not invited]
     
    Japanese kelp (Saccharina japonica) is one of the most valuable cultured and harvested kelp species in Japan. In this study, we added a physical parameter, sea surface nitrate (SSN) estimated from satellite remote sensing data, to develop a suitable aquaculture site-selection model (SASSM) for hanging cultures of Japanese kelp in southern Hokkaido, Japan. The local algorithm to estimate SSN was developed using satellite measurements of sea surface temperature and chlorophyll-a. We found a high correlation between satellite-and ship-measured data (r(2) = 0.87, RMSE = 1.39). Multi-criteria evaluation was adapted to the SASSM to rank sites on a scale of 1 (least suitable) to 8 (most suitable). Wefound that 64.4% of the areas were suitable (score above 7). Minamikayabe was identified as the most suitable area, and Funka Bay also contained potential aquaculture sites. In addition, we examined the impact of El Nino/La Nina-Southern Oscillation (ENSO) events on Japanese kelp aquaculture and site suitability from 2003-2010. During El Nino events, the number of suitable areas (scores 7 and 8) decreased significantly, indicating that climatic conditions should be considered for future development of marine aquaculture.
  • Toshiki Uji, Hiroyuki Mizuta, Naotsune Saga
    MARINE BIOTECHNOLOGY 15 (2) 188 - 196 1436-2228 2013/04 [Refereed][Not invited]
     
    The life cycle of plants entails an alternation of generations, the diploid sporophyte and haploid gametophyte stages. There is little information about the characteristics of gene expression during each phase of marine macroalgae. Promoter analysis is a useful method for understanding transcriptional regulation; however, there is no report of promoter analyses in marine macroalgae. In this study, with the aim of elucidating the differences in the transcriptional regulatory mechanisms between the gametophyte and sporophyte stages in the marine red alga Porphyra yezoensis, we isolated the promoter from the sporophyte preferentially expressed gene PyKPA1, which encodes a sodium pump, and analyzed its promoter using a transient gene expression system with a synthetic beta-glucuronidase (PyGUS) reporter. The deletion of -1432 to -768 relative to the transcription start site resulted in decreased GUS activity in sporophytes. In contrast, deletion from -767 to -527 increased GUS activity in gametophytes. Gain-of-function analyses showed that the -1432 to -760 region enhanced the GUS activity of a heterologous promoter in sporophytes, whereas the -767 to -510 region repressed it in gametophytes. Further mutation and gain-of-function analyses of the -767 to -510 region revealed that a 20-bp GC-rich sequence (-633 to -614) is responsible for the gametophyte-specific repressed expression. These results showed that the sporophyte-specific positive regulatory region and gametophyte-specific negative regulatory sequence play a crucial role in the preferential expression of PyKPA1 in P. yezoensis sporophytes.
  • Development of self-reliant bio-farming system by employing natural energy.
    Kimura N, Fujimori Y, Yasui H, Mizuta H, Abe T. Adachi, S, Takahashi Y
    FFTC Extension Bulletin (661) 1 - 10 2013 [Refereed][Not invited]
  • Hiroyuki Mizuta, Hajime Yasui
    JOURNAL OF APPLIED PHYCOLOGY 24 (5) 1177 - 1182 0921-8971 2012/10 [Refereed][Not invited]
     
    We investigated biogenic silica deposition in sporophytes of kelp, Saccharina japonica (Laminariaceae). Silicon content was measured in different sporophyte regions and there was a trend for the silicon content to increase longitudinally from the stipe-blade transition to apical regions. The transverse trend was for the content to be higher in the marginal region than in the medial region. The silicon content was also higher in the scar and sorus regions compared with the adjacent vegetative regions. High silicon content was detected in the margin of the disc and in the sorus region of cultured sporophyte discs. Moreover, rhodamine 123 staining suggested that silicon was deposited in the mouth of the marginal wound of the disc. Rhodamine 123 fluorescence was also detected in the paraphyses and mucilaginous caps of sori. These results suggest that silicon plays important roles in tissue protection and vegetative tissue wound healing. It is also suggested that silicon is required for the protection of reproductive tissues. We also discuss the physiological and ecological roles of biogenic silica deposition in kelp and its management in cultivated fields.
  • Toshiki Uji, Ryota Monma, Hiroyuki Mizuta, Naotsune Saga
    FISHERIES SCIENCE 78 (5) 985 - 991 0919-9268 2012/09 [Refereed][Not invited]
     
    Na+/H+ antiporters are known to play a crucial role in pH and Na+ homeostasis. In the present study, we characterized the molecular structures and expression patterns of two Na+/H+ antiporters from the marine red alga Porphyra yezoensis (designated PySOS1 and PyNhaD). The full-length cDNAs of PySOS1 and PyNhaD were 5122 and 1804 bp, and contained open reading frames (ORFs) of 4773 and 1275 bp, respectively. The deduced amino acid sequences showed high similarity to SOS1 and NhaD from the higher plant Arabidopsis thaliana. PySOS1 and PyNhaD contained conserved sequences found in the cation-proton antiporter. Quantitative real-time PCR analysis revealed that both antiporter genes were expressed in both the gametophyte and sporophyte of P. yezoensis. In addition, mRNA expression of PySOS1 and PyNhaD was simultaneously upregulated by light irradiation, suggesting that coordinated activity between the two is important in pH and Na+ homeostasis under light conditions. Moreover, the expression levels of both genes were partially reduced by the photosynthetic inhibitors DCMU and DBMIB, suggesting that upregulation is linked to photosynthesis-related metabolism. These findings provide an initial step towards understanding Na+/H+ antiporters in marine red algae.
  • Miwa Kanamori, Hiroyuki Mizuta, Hajime Yasui
    JOURNAL OF APPLIED PHYCOLOGY 24 (4) 701 - 706 0921-8971 2012/08 [Refereed][Not invited]
     
    Explants obtained from young sporophytes of Saccharina japonica were cultured in an artificial medium with different concentrations of Ca2+ (0-20 mM). The culture with 10 mM Ca2+ promoted the formation of unpigmented filamentous callus-like cells in the cortical layer. In contrast, explants cultured with 5 mM Ca2+ formed pigmented round callus-like cells in the epidermis at a high percentage. The thallus regeneration rate of explants in 5 mM Ca2+ was ten times higher than those of explants cultured in 10 mM Ca2+. Ambient Ca2+ concentrations also influenced the production of radical oxygen species (ROS) in explants. Explants cultured in 10 mM Ca2+ produced higher ROS than did those cultured in 5 mM. The ROS production was histologically observed mainly in the plasma membrane of callus-like cells using 2', 7'-dichlorodihydrofluorescein diacetate. Moreover, a nicotinamide adenine dinucleotide phosphate (NADPH) oxidase inhibitor, diphenyleneiodonium chloride, inhibited the ROS production with propagation of filamentous callus-like cells. These results suggest that Ca2+ concentration in medium influences the development of callus-like cells and thallus regeneration by affecting NADPH oxidase activity and ROS production in the plasma membrane of the callus-like cells. Therefore, the morphological form of callus-like cells and the development of thallus will be controlled by Ca2+ concentration in the medium.
  • Takahashi, M, Mikami, K, Mizuta H, Saga, N
    J. Aquac. Res. Development OMICS Group 2 (4) 4  2155-9546 2011 [Refereed]
     
    Despite the development of transient gene expression in red algae Porphyra species, a stable transformationsystem has not been established in these algae yet. One reason for the difficulty in the transformation is the lackof a way to select transformed cells from the algae. Thus, to identify antibiotics suitable for the selection of stablytransformed cells, we tested the gametophyte for sensitivity to 6 antibiotics, ampicillin (Am), kanamycin (Km),hygromycin (Hm), geneticin (G418), chloramphenicol (Cm) and paromomycin (Pm), which are frequently employedas selection agents in the transformation of land plants and microalgae. Sensitivity tests, which were carried out withdifferent concentrations (0-10 mg mL-1) of antibiotics, showed that Hm, G418, Cm and Pm exhibited a lethal effect atmore than 1.0 mg mL-1, suggesting the suitability of these four antibiotics for the selection of genetically transformedcells from P. yezoensis gametophytes, while P. yezoensis gametophytes were highly resistant to Am and Km. Wealso succeeded in reducing the antibiotic concentrations by lowering the pH value and salt concentration using anartificial synthetic medium. Increasing the sensitivity of gametophytic cells to Hm, G418, Cm and Pm in the modifiedsynthetic medium will contribute to establishing a genetic transformation system in P. yezoensis.
  • Hiroyuki Mizuta, Hajime Yasui
    BOTANICA MARINA 53 (5) 409 - 416 0006-8055 2010/10 [Refereed][Not invited]
     
    We investigated production of radical oxygen species (ROS) in sorus development of sporophyte discs and during zoospore germination of Saccharina japonica (Phaeophyceae) using the fluorescent dye 2',7'-dichlorofluorescein diacetate (DCFH-DA). Quantitative analysis of ROS showed high intracellular production during the stages of zoosporangium formation when paraphyses elongated. In this stage, remarkable ROS release was observed. ROS production was also observed histologically (under a fluorescence microscope) in the elongating paraphyses and the sorus zoosporangia. The sorus had significantly higher phenol content, antioxidant capacity and ROS scavenging enzyme activities (ascorbate peroxidase, catalase, glutathione reductase and superoxide dismutase) than adjacent non-sorus blade sectors. Thus, intracellular ROS scavenging mechanisms are active during ROS production in sorus formation. In contrast, iodine content was lower in the sorus than in the adjacent non-sorus tissues, suggesting the existence of an antioxidant defense mechanism based on iodine efflux. We demonstrated that ROS production is an important phenomenon in the reproduction of the S. japonica sporophyte. Furthermore, ROS were also observed in the zoospore germination processes. We discuss the physiological and ecological roles of ROS production in sorus formation and zoospore germination.
  • Simple method for estimating fucoidan and laminaran contents in several brown algae
    AKITA Y. MIZUTA H, YASUI H
    Algal Resources 3 93 - 98 2010 [Refereed][Not invited]
  • Katsuhiro Tabuchi, Hiroyuki Mizuta, Hajime Yasui
    AQUACULTURE RESEARCH 41 (1) 1 - 10 1355-557X 2009/12 [Refereed][Not invited]
     
    The effects of 5-aminolevulinic acid (ALA) on the induction and growth of callus-like cells in Laminaria japonica were investigated in explants obtained from basal, middle and apical portions along the sporophyte. 5-Aminolevulinic acid treatment promoted the induction of callus-like cells in explants obtained from all portions, and the induction rate was higher when a concentration of 50-500 mg L-1 of ALA was used. The promotion was especially remarkable in apical explants, and the induction was 10-14 times higher in the 100-500 mg L-1 range than that in the 0 mg L-1. The cell division rate of callus-like cells showed the highest value in the explants cultured with 500 mg L-1 of ALA for 14 days. The promotion of the cell division rate by culturing with 500 mg L-1 ALA was also observed under white, blue and red lights. The callus-like cells, which were cultured in 500 mg L-1 of ALA for 2 months, had many clear chloroplasts. After 3 months, young thalli occurred. These results suggest that the ALA treatment is effective for stable propagation of callus-like cells in L. japonica.
  • Hirotoshi Endo, Eun-Jeong Park, Youichi Sato, Hiroyuki Mizuta, Naotsune Saga
    FISHERIES SCIENCE 75 (2) 393 - 400 0919-9268 2009/04 [Refereed][Not invited]
     
    As a trial to develop a method of authenticating the place of origin of circulated Undaria pinnatifida products, we investigated their intraspecific genetic diversity using the mitochondrial cytochrome c oxidase subunit 1 gene (cox1) and the internal transcribed spacer 2 (ITS2) region of the nuclear ribosomal DNA (rDNA) sequence. Four dried U. pinnatifida products labeled with their origins (one from Japan, one from China and two from Korea), natural plants collected from three locations (two from Japan and one from China), and cultivated plants collected from two locations (one from Japan and one from China) were used in the present study. The amplified fragments of cox1 were 664 bp in length, and the aligned sequences were highly homologous. Among the nine sequences, no insertions or deletions were found and six substitution positions were detected, and they were classified into five haplotypes. In contrast, multiple highly variable regions were found in ITS2, and some of them carried a restriction site for Mbo II. Polymerase chain reaction-restriction fragment length polymorphism analysis showed different restricted profiles among the tested samples. The availability of molecular markers for authenticating food products of U. pinnatifida is discussed.
  • Ako Saito, Hiroyuki Mizuta, Hajime Yasui, Naotsune Saga
    AQUACULTURE 281 (1-4) 138 - 144 0044-8486 2008/09 [Refereed][Not invited]
     
    A dioecious red alga, Porphyra pseudolinearis, which does not produce asexual spores such as archeospore, is a commercially valuable Porphyra seaweed. We obtained a large amount of regenerable free cells of P. pseudolinearia by gentle homogenization in seawater after culturing the thalli in nutrient-rich medium with 10 mM of allantoin at 15 degrees C and 20 degrees C. The obtained free cells were divided into three forms: globular, elliptic and 2-celled. These free cells formed cell walls slowly compared to conchospores, and they directly developed to thalli or filamentous germlings like conchocelis or conchosporangia. In particular, the occurrence of thalli was remarkable in free cells obtained from the thalli cultured with 10 mM allantoin at 20 degrees C. Once the free cells developed to the thalli, they showed the same rates of growth to the thalli generated from conchospores, and they grew to be more than 50 cm in blade length. This technique to produce regenerable free cells from the Porphyra species that do not produce archeospores is useful for vegetative propagation and breeding. (C) 2008 Elsevier B.V. All rights reserved.
  • 高橋 潤, 富松亮介, 遠藤博寿, 北出幸広, 水田浩之, 嵯峨直恆
    Fish genetics and breeding science 水産育種研究会 37 (1) 19 - 27 1343-7917 2008 [Refereed][Not invited]
  • Hiroyuki Mizuta, Tomoki Kai, Katsuhiro Tabuchi, Hajime YAsui
    AQUACULTURE RESEARCH 38 (12) 1323 - 1329 1355-557X 2007/09 [Refereed][Not invited]
     
    Responses of the sporophytes of Laminaria japonica to blue, red and white lights were investigated using segments, discs and whole plants. The relative growth rate with regard to the blade's length and width showed no difference among the light conditions during 2 weeks of culturing. On the contrary, the elongation rates of the stipe and the holdfast were 1.7-2.5 times higher under red light than that under white light as a control. Callus formation in the segments was also promoted more under red light conditions than under white or blue light. Blue light irradiation resulted in a 48% and 12% decrease in the relative growth rate of the stipe and the holdfast, respectively, in comparison with the control. When sporophyte discs were cultured for 10 weeks, all discs formed zoosporangial sori 2-3 weeks earlier under blue light than under white light. However, red light inhibited the formation of zoosporangia. Indoleacetic acid (IAA) oxidase activity was about two-fold higher under blue light than under red light, suggesting that the difference in response between the blue and red light conditions is related to the internal IAA level of the tissues. The developmental, reproductive and morphological effects of blue and red lights will be useful for the artificial control of the life cycle of Laminaria plants and for the development of more efficient cultivation techniques.
  • NAKATA Kazuyoshi, YAMAZAKI Tomoyasu, MIZUTA Hiroyuki, KAWAI Tadashi, ITO Hiroshi, GOSHIMA Seiji
    Suisanzoshoku 水産増殖談話会 54 (3) 375 - 381 0371-4217 2006/09 [Refereed][Not invited]
     
    We made two laboratory experiments with small herbivorous gastropods Omphalius rusticus rusticus and Chlorostoma lischkei that frequently live in the habitats of the kelp Laminaria religiosa in southwest Hokkaido, Japan, to examine the effect of their grazing on L. religiosa at different water temperatures. In an experiment to find if O. rusticus rusticus feeds on a sheet of kelp gametophytes settled on styrene chambers or on glass slides at 5°C, 10°C and 15°C, O. rusticus rusticus fed on the kelp gametophytes even at the lowest water temperature, but food consumption increased as the water temperature increased. In an experiment to find if the two gastropod species feed on juvenile kelp sporophytes at 10°C and 15°C, many individuals of C. lischkei actively fed on juvenile kelp sporophytes at both water temperatures, but most individuals of O. rusticus rusticus showed no preference regardless of water temperature. Our results suggest that the potential impact of gastropod grazing on L. religiosa might differ between these gastropod species and water temperatures.
  • Takeshi Kumura, Hajime Yasui, Hiroyuki Mizuta
    FISHERIES SCIENCE 72 (4) 860 - 869 0919-9268 2006/08 [Refereed][Not invited]
     
    Sporophyll formation in two alariaceous plants, Undaria pinnatifida and Alaria crassifolia, was studied in relation to the nutrient requirements. The sporophylls of U pinnatifida formed zoosporangia when they had N and P contents greater than 1.4 kgN/m(3) and 0.74 kgP/m(3). This indicates that these values are the critical nutrient levels for zoospore formation in U. pinnatifida. In the sporophytes of A. crassifolia, many sporophylls with zoosporangia showed nutrient contents higher than 6.25 kgN/m(3) and 1.70 kgP/m(3). These results suggest that the U. pinnatifida can form zoospores at lower levels of N and P contents than A. crassifolia. Both species often formed zoosporangial sori on the blades in the late period of each reproductive season. The fertile parts of the blade showed N and P contents higher than the critical levels. This phenomenon indicates that the blades have the capability to form zoosporangial sori if there is a sufficient accumulation of nutrients for zoospore formation. The zoospore formation on the blade seems to be accomplished by an overflow of excess nutrients from sporophylls into the blade, or by accumulating sufficient nutrients to form sori even if the sporophylls are not formed.
  • NAKATA Kazuyoshi, YAMAZAKI Tomoyasu, MIZUTA Hiroyuki, KAWAI Tadashi, ITO Hiroshi, GOSHIMA Seiji
    Suisanzoshoku 水産増殖談話会 54 (2) 217 - 224 0371-4217 2006/06 [Refereed][Not invited]
     
    北海道南西部の日本海沿岸で見られる藻場の消失に、植食性小型巻貝類が及ぼす影響について調べる上で必要となる基礎的知見を得ることを目的に、研究を実施した。まず、小型巻貝4種（クボガイ、コシダカガンガラ、エゾサンショウ、クロタマキビ）によるホソメコンブに対する摂餌痕跡を室内実験で観察した。スチロール樹脂製容器とスライドグラスに着生させたホソメコンブの配偶体をこれら4種の巻貝に摂餌させたところ、すべての巻貝種で配偶体の摂餌が継続的に確認され、巻貝種間で特徴の異なる摂餌痕跡が観察された。この摂餌痕跡の種間差は、歯舌の形態と大きさや摂餌様式が巻貝種間で異なることが影響したと考えられた。次に、野外で採集したホソメコンブの胞子体を観察したところ、小型巻貝による歯舌の痕跡と思われる形跡が多数観察された。以上から、植食性小型巻貝がホソメコンブ群落に何らかの影響を与える可能性が示唆された。
  • Tomoki Kai, Kazumi Nimura, Hajime Yasui, Hiroyuki Mizuta
    JOURNAL OF APPLIED PHYCOLOGY 18 (1) 95 - 101 0921-8971 2006/02 [Refereed][Not invited]
     
    Young sporophytes of Laminaria japonica Areshoug were cultured in six indole-acetic acid ( IAA) concentrations ( 0, 10(-8), 10(-7), 10(-6), 10(-5), 10(-4) M) to examine the effect of auxin on growth. The effects of auxin on sorus formation were also examined by using discs taken from the adult sporophyte. The auxin contents and IAA oxidase activities in the thallus and sorus parts of the sporophyte were determined with the blade and sporophyll of other Laminariales plants, Undaria pinnatifida ( Harvey) Suringar and Alaria crassifolia Kjellman. The young sporophytes of L. japonica showed highest elongation rate in 10(-5) MIAA. In contrast, the sorus formation on the discs cultured in 10(-5) MIAA was markedly delayed in comparison with other concentrations, indicating that sorus formation was suppressed by IAA. Free and conjugated auxin contents were lower in the reproductive parts than in the vegetative parts. In three Laminariales sporophytes, IAA oxidase activity was about 3-9 times higher in the reproductive parts than in the vegetative parts. Taken together these results suggest that the growth and reproduction of Laminariales sporophytes are regulated by internal auxin levels. Elucidating the regulation mechanism is likely to provide information that is important for the management of plant production and the assessment of the physiological status of plants in the field.
  • KAWAGOE Chikara, TANI Takashi, INDY Jeane Rimber, MIZUTA Hiroyuki, YASUI Hajime
    Aquaculture Science 水産増殖談話会 53 (2) 181 - 187 2185-0194 2005/06 [Refereed][Not invited]
     
    北方海域において、フシスジモクの計画的な増殖を展開する際に基礎となる育成技術を開発する目的で、異なる水温下で受精卵から幼体までの形態形成過程を明らかにし、幼胚、幼体生長に適した条件を決定した。2000年6月に江差町沿岸のフシスジモク群落より受精卵を採取し、光周期12h明期：12h暗期、光量40μE／m2／s、 水温3℃、5℃、10℃、15℃、20℃ で静置培養した。水温3℃では、7日後に1次仮根胚となり、その後発生は停滞した。水温5℃では、60時間後に1次仮根胚、10日後に2次仮根胚となり、発生が停滞した。水温10℃では、48時間後に1次仮根胚、7日後に2次仮根胚、1年後に主軸形成体となった。水温15℃では、36時間後に1次仮根胚、5日後に2次仮根胚、2カ月後に主軸形成体、3カ月後に付着器形成体、6カ月後に主枝形成体となった。水温20℃では、36時間後に1次仮根胚、3日後に2次仮根胚、1カ月半後に主軸形成体、3カ月後に付着器形成体、6カ月後に主枝形成体となったが、付着器形成体の段階で枯死する個体が見られた。以上から、水温15℃は北海道産フシスジモクの幼胚、幼体の生長に適していることがわかった。また、水温 3℃、5℃は幼胚を長期保存するのに適した水温であることを認めた。
  • 冨松亮介, 高橋潤, 遠藤博寿, 北出幸広, 水田浩之, 嵯峨直恆
    水産育種 水産育種研究会 34 (2) 123 - 128 1343-7917 2005 [Refereed]
  • MORI Shunsuke, YAMAZAKI Ayano, MATSUYAMA SERISAWA Kazuyo, FUKUDA Satoru, MIZUTA Hiroyuki, SAGA Naotsune
    Aquaculture Science 水産増殖談話会 52 (3) 239 - 244 2185-0194 2004/09 [Refereed][Not invited]
     
    Symbiotic bacteria BPY-W6 and BPY-W8 were added to an axenic culture strain (TU-1) of Porphyra yezoensis, and the length and width of gametophyte of the organism were measured. Axenic cultures of the gametophyte were used as a control. Area and morphological index value (MIV) were calculated on the basis of the length and width measured. After culture for 42 days, the form of the control strain became the callus-like masses, and the strains which added bacteria became monostromatic gametophytes. The strain in which the average length was most lengthened was one added BPY-W8. The strain in which the average width was most lengthened was one added BPY-W6. The strain in which the average area increased most was one added BPY-W6. Throughout the measurement period, MIV for the strain added BPY-W8 was bigger than that of the strain added BP-YW6. It was suggested that BPY-W6 was the bacteriostrain of which the effect for the elongation of the width is big and tended to form the ova-like gametophyte, and BPY-W8 was the bacteriostrain of which the effect for the elongation of the length is big and tended to form the elliptical-like gametophyte from these results.
  • Mizuta Hiroyuki
    Bulletin on coastal oceanography The Oceanographic Society of Japan (OSJ) 41 (1) 33 - 38 1342-2758 2003/08 [Refereed][Invited]
     
    Laminaria plants distribute in the coastal regions of Hokkaido and the northern mainland of Japan. Some species which distribute in the Coastal Oyashio region are industrially important resources by their high production. Generally, the distribution of Laminaria species can be explained on the basis of water temperature. In this symposium, the relationship between the distribution of four Laminaria species and the nutrient requirements in their reproduction was discussed by measuring their reproductive efforts and nutrient contents. Laminaria longissima and L. angustata (cold-current specie...
  • Hiroyuki Mizuta, Hajime Yasui, Naotsune Saga
    Journal of Applied Phycology 15 (4) 345 - 349 0921-8971 2003/07 [Refereed][Not invited]
     
    A simple method is presented for obtaining a large number of monospores in the thallus of Porphyra yezoensis. The method implies two principles: induction of monosporangium formation by allantoin, and liberation of monospores from the cell wall by mild homogenization. The induction of monosporangium formation was accomplished by culturing wild thalli in nutrient-enriched seawater with 10 mM of allantoin for approximately 3 weeks. This high concentration (10 mM) of allantoin suppressed the growth of the thalli compared with lower concentrations (0-1 mM). Thalli cultured for 3 weeks were mildly homogenized with a glass homogenizer and the monospore solution was obtained by filtering with a nylon mesh. The monospores grew normally to thalli. This technique of monospore acquisition is a simple and useful method for the propagation and breeding of P. yezoensis thalli.
  • H Mizuta, S Ogawa, H Yasui
    AQUATIC BOTANY 76 (2) 117 - 126 0304-3770 2003/06 [Refereed][Not invited]
     
    The relationship between phosphorus uptake and internal phosphorus status was studied on the kelp species, Laminaria japonica Areshoug. Elongation of the cultivated sporophyte ceased after June when phosphorus content was less than 1.3 mug P (g DW)(-1), indicating that this is the critical phosphorus content required for growth. The uptake rates of inorganic phosphorus, organic phosphorus, and extracellular alkaline phosphatase rapidly increased when the phosphorus content decreased to the critical level. These results suggest that phosphorus acquisition by the sporophyte is closely linked to the internal phosphorus level. Moreover, nucleic acid content correlated to the phosphorus content when the level of phosphorus was greater than the critical value, suggesting that the critical phosphorus content is a good indicator of phosphorus requirement and utilization within the plant. (C) 2003 Elsevier Science B.V. All rights reserved.
  • Y Fukuhara, H Mizuta, H Yasui
    FISHERIES SCIENCE 68 (6) 1173 - 1181 0919-9268 2002/12 [Refereed][Not invited]
     
    The release of zoospores from zoosporangia in Laminaria japonica mainly occurred at night. The maximum swimming speed of the zoospores was observed immediately after release (similar to160mum/s), and then decreased with time. The zoospores exhibited clear chemotaxis to high concentrations of nitrate-N and phosphate-P. Only half of the zoospores were observed to swim against seawater with a flow velocity of 124 mum/s. The zoospores became floating spores after they stopped swimming in the seawater. Low light and low water temperature conditions prolonged the swimming period of the zoospores. However, the photosynthesis of the zoospores was suppressed in low water temperatures, and was also limited under high light irradiance. These results suggest that photosynthesis in zoospores does not prolong their swimming period, and that when their swimming energy is exhausted, floating spores appear.
  • K Nimura, H Mizuta
    JOURNAL OF APPLIED PHYCOLOGY 14 (3) 159 - 163 0921-8971 2002/06 [Refereed][Not invited]
     
    The effects of exogenous abscisic acid (ABA; 10(-7)-10(-5) M), a known plant growth regulator, on reproduction and growth were investigated by culturing discs from sporophytes of Laminaria japonica Areschoug. ABA plays a role in triggering sorus formation, and it was found that sorus formation of discs was fastest in 10(-5) M ABA. The application of 10(-5) M ABA to culturing discs also suppressed the expansion of surface area. ABA contents in sorus and vegetative parts of the sporophyte were determined by bioassay. The mean ABA content in sorus parts obtained from sporophytes was 0.222 +/- 0.053 mug equivalent-ABA g wet weight(-1), which was about five times higher than the content found in vegetative parts (0.048 +/- 0.009 mug equivalent-ABA g wet weight(-1)). Taken together these results suggest that sorus development requires an elevated level of ABA and is associated with decreasing vegetative growth and that the ABA level of the sporophyte may play a crucial role in reproduction.
  • NIMURA Kazumi, MIZUTA Hiroyuki
    Suisanzoushoku 水産増殖談話会 50 (2) 157 - 162 2185-0194 2002/06 [Refereed][Not invited]
     
    マコンプの子嚢斑形成について胞子体から得た藻体片を培養し、子嚢斑形成様式を調べた。鉛直的に切り出した藻体片ではそれらの基部側に子嚢斑が形成された。一方、水平に切り出した藻体片においては、縁辺部と基部の移行部に子嚢斑が形成された。中帯部と縁辺部を切り離し培養した結果、中帯部では基部側から成熟し、縁辺部では中帯部側に子嚢斑が形成された。子嚢斑が形成される部位は栄養塩が蓄積しやすいシンク(供給先)に相当する。子嚢斑の形成部位は胞子体内での栄養塩の移動が関与していると推察した。
  • K Nimura, H Mizuta, H Yamamoto
    BOTANICA MARINA 45 (2) 184 - 188 0006-8055 2002/03 [Refereed][Not invited]
     
    The critical contents of nitrogen and phosphorus for sorus formation in Laminaria angustata, L. japonica, L. ochotensis and L. religiosa were measured using cultured discs cut from the sporophytes. In L. japonica, fertile sporophytes were also used. Discs were cultured in Provasoli's enriched seawater or nutrient-poor seawater at 10 degreesC under 100 mumol photons m(-2) s(-1) of irradiance (12L:12D). Regardless of the nutrient conditions in the culture media, the contents of nitrogen and phosphorus in the sorus part of discs and sporophytes of L. japonica were above 1.78 mg N cm(-3) and 0.19 mg P cm(-3) respectively, showing these values are critical for sorus formation in this species. Discs of L. angustata, L. ochotensis and L. religiosa in PES had higher contents of nitrogen and phosphorus in sorus parts than in L. japonica. The sorus area increased with accumulation of nitrogen or phosphorus in all species, but in L. angustata it was small despite the high contents of nitrogen and phosphorus, showing that this alga has a high nutritional cost in reproduction that might be a physiological adaptation to cold and nutrient-rich habitats.
  • Relationship between phycoerythrin and nitrogen content in Gloiopeltis furcata and Porphyra yezoensi
    Hiroyuki Mizuta, Yasuhiro Shirakura, Hirotoshi Yamamoto
    Algae 17 89 - 93 2002 [Refereed][Not invited]
  • A Ozaki, H Mizuta, H Yamamoto
    FISHERIES SCIENCE 67 (3) 415 - 419 0919-9268 2001/06 [Refereed][Not invited]
     
    The nutrient uptake kinetics of Kjellmaniella crassifolia and Laminaria japonica were determined under a variety of conditions. The nitrate and phosphate uptake rates followed Michaelis-Menten kinetics toward ambient nutrient concentrations, showing no difference between the maximum uptake rates of the two species. However, half-saturations of nitrate and phosphate uptake kinetics in K. crassifolia were higher than those in L. japonica. Low water temperature (5 degreesC) greatly restrained the nitrate and phosphate uptakes of both algae. Low irradiance (< 100 muE/m(2) per s) restrained nitrate and phosphate uptakes only in L. japonica, although high irradiance (> 100 muE/m(2) per s) caused no difference between the two species. The nitrate and phosphate uptake rates at low irradiance in K. crassifolia were 2-7 times higher than those in L. japonica. Light compensation and saturation irradiances in K. crassifolia were significantly lower than in L. japonica. These results indicate that K. crassifolia is able to take up carbon and nutrients at low irradiance, which suggests that the nutrient uptake characteristic of K. crassifolia could allow it to adapt to deeper habitats and even to high water turbidity.
  • MIZUTA Hiroyuki, NARUMI Hideto, YAMAMOTO Hirotoshi
    Suisanzoshoku 水産増殖談話会 49 (2) 175 - 180 2185-0194 2001/06 [Refereed][Not invited]
     
    Zoospores of Laminaria religiosa were cultured for 81-97 days in different nitrate (0-100 μM) and phosphate (0-10 μM) concentrations in order to examine the effects of nitrate and phosphate on the growth and maturation of gametophytes in batch culture. The female gametophytes matured and formed sporophytes at concentrations of more than 5.0 μM nitrate and more than 1.0 μM phosphate. These are the critical levels necessary for allowing the development from a gametophyte into a sporophyte, in cases when the maturation of the gametophyte is limited by both nitrate and phosphate. The critical nitrate concentration decreased to 1.0 μM when the phosphate concentration was sufficient, and the critical phosphate concentration similarly decreased to 0.5 μM when the nitrate level was sufficient, indicating that the critical concentration is affected by the synergy between the concentrations of two nutrients. The effects of irradiance (0.76-14.8 μE/m2/s) and water temperature (5-15°C) on gametophyte maturation and sporophyte formation were also examined in six nutrient concentrations. Low nutrient concentration or low irradiance independently delayed maturation and formation, showing that the reproduction of L. religiosa gametophytes is controlled by the accumulation of nutrients in a plant and by quantum dose.
  • Shigeo Ichiki, Hiroyuki Mizuta, Hajime Yasui, Hirotoshi Yamamoto
    Bull. Fac. Fish. Hokkaido Univ. 北海道大学 52 (2) 103 - 109 1346-1842 2001 [Not refereed][Not invited]
  • Differences in photosynthesis and nucleic acid content between sterile and fertile parts of the sporophyte of Laminaria japonica (Phaeophyceae)
    Kazumi Nimura, Hiroyuki Mizuta
    Algae 16 151 - 155 2001 [Refereed][Not invited]
  • S Ichiki, H Mizuta, H Yasui, H Yamamoto
    PHYCOLOGIA 39 (5) 408 - 415 0031-8884 2000/09 [Refereed][Not invited]
     
    Nonnucleate, uninucleate. binucleate, trinucleate and tetranucleate spores were found in sporophytes of Lithophyllum yes soense. The formation of polynucleate spores was caused mainly by the irregular distribution of nuclei in tetrasporangia. Both nuclei in a binucleate spore took part in development, suggesting that polynucleate spores grow into chimaeric crusts. The relative growth rate was higher in sporelings developed from trinucleate and tetranucleate spores (c. 12% d(-1)) than from uninucleate and binucleate spores (c. 5% d(-1)). However, the survival rates of sporelings developed from trinucleate and tetranucleate spores were less than half of those developed from uninucleate and binucleate spores. Polynucleate spores frequently occurred at low water temperature, especially at less than 12.1 degreesC. indicating that successful reproduction via spores would be limited by low water temperature in winter, although this is when spore production is highest in southwestern Hokkaido.
  • Shigeo Ichiki, Hiroyuki Mizuta, Hirotoshi Yamamoto
    Phycological Research 48 (2) 115 - 120 1322-0829 2000 [Refereed][Not invited]
     
    Lithophyllum yessoense Foslie is a markedly dominant subtidal, crustose coral line alga in south-western Hokkaido, Japan. In this study, the effects of irradiance, water temperature and nutrients (nitrate and phosphate) on the growth of sporelings of the alga were examined. The relative growth rate (RGR) was saturated at 17.6% d-1 at a high irradiance (240 μmol photon m-2 s-1). Even at a low irradiance (10.7-49.9 μmol photon m-2 s-1), RGR was 7.1-12.7% d-1. The survival rate of sporelings was greater than 80% at irradiance above 10.7 μmol photon m-2 s-1 throughout the culture period. The growth of L. yessoense sporelings was promoted at 15°C and 20°C, but inhibited at 5°C. The half-saturation constants (Ks) for growth were about 0.5 μmol L-1 and 0.14 μmol L-1 for nitrate and phosphate, respectively. Saturated nitrate and phosphate concentrations for the growth were about 4.0 μmol L-1 and 0.4 μmol L-1, respectively, suggesting that L. yessoense is adaptable to a relatively high water temperature, a wide range of irradiance, and low ambient nitrate and phosphate concentrations. The results provide a possible explanation of why L. yessoense is dominant in the environments of south-western Hokkaido.
  • H Mizuta, K Nimura, H Yamamoto
    FISHERIES SCIENCE 65 (1) 104 - 108 0919-9268 1999/02 [Refereed][Not invited]
     
    Optimal conditions for sorus formation of Laminaria japonica were investigated by culturing discs of the sporophyte in bottles. All discs formed sori in the seven combinational conditions of temperature (5-15 degrees C), irradiance (33.2-11.6 mu E.m(-2).s(-1)) and photoperiods (16:8, 12:12 and 8:16 h LD) in nutrient-rich medium. Sorus formation occurred earlier at 15 degrees C than at 5 and 10 degrees C and were largest in the area at 15 degrees C. Sori grew larger under high irradiance (116 mu E.m(-2).s(-1)) than under low irradiances (66.4 and 33.2 mu E.m(-2).s(-1)), but the initiation of sorus formation was not influenced by irradiance. Sorus formation was earlier in 8:16 h LD than in 12:12 and 16:8 h LD. Rapid formation of large sori occurred at high temperatures even in a long photoperiod. Sorus formation in discs in nutrient-poor medium was slower than that in discs in nutrient-rich medium, in which all discs formed large sori. Most discs in nutrient-poor medium formed very small sori. These results indicate that water temperature and nutrient conditions strongly affect both to the induction and expansion of sorus formation.
  • H Mizuta, K Nimura, H Yamamoto
    JOURNAL OF APPLIED PHYCOLOGY 11 (6) 585 - 591 0921-8971 1999 [Refereed][Not invited]
     
    Sorus formation on median and marginal parts of Laminaria japoncia Areschoug was investigated by cultivating sporophytes from December 1996 to September 1997 in Southern Hokkaido, Japan. Simultaneously, discs (ca. 3 cm in diameter) that were cut off monthly from median and marginal parts of the cultivated sporophytes were incubated in our laboratory. All the cultivated sporophytes formed sori on the median parts from January to August, while all the median and marginal discs formed sori at 10 degrees C at 46 mu mol photon m(-2)s(-1) (12L:12D) in enriched medium. There was no difference in sorus area between median and marginal discs. These results indicated that the marginal parts are able to produce sori, although the greater part of them are actually washed away before forming sori in the sea. The marginal part is probably in a state of 'resource limitation' on the reproduction because the resource outflowed from this part to the basal part for the growth of sporophytes.
  • H Mizuta, J Hayasaki, H Yamamoto
    FISHERIES SCIENCE 64 (6) 909 - 913 0919-9268 1998/12 [Refereed][Not invited]
     
    Seasonality of reproduction in sporophytes of Laminaria japonica was investigated on the basis of the nitrogen content of thalli cultivated in the field in southern Hokkaido, Japan. Fertile plants occurred throughout most of the year. Sorus formation was greatest in the basal parts of thalli in fall (September). The secondary peak of sorus formation occurred in the apical parts of thalli in winter (February and March). The seasonality of sorus formation was linked closely to the nitrogen content in the thalli. The nitrogen content per volume of thalli declined from January to April and then increased to a maximum in September. In January and February, the nitrogen content was higher in the apical part (ca. 2 mg.cm(-3)) than in the basal part of thalli. After June, however, it was higher in the basal part. Sorus area increased in association with the nitrogen content per volume of thalli regardless of the thallus part or season. In addition, although sorus formation took more than 100 days after April, it needed only about 50 days in February. These results suggest that the low nitrogen content in summer delayed sorus formation and decreased the area of the sori. The onset and position of sorus formation depended on the growth and the nitrogen content per volume of each thallus.
  • H Mizuta, K Torii, H Yamamoto
    FISHERIES SCIENCE 63 (4) 553 - 556 0919-9268 1997/08 [Refereed][Not invited]
     
    Relations among carbon and nitrogen contents, photosynthetic capacity and surface-to-volume ratio were investigated using the discs cut from sporophytes of Laminaria japonica Areschoug. The relation between the carbon and nitrogen contents was divided into three phases on the basis of two distinctive nitrogen content levels, namely the subsistent and critical values. The first phase was characterized by a positive correlation between carbon and nitrogen amounts when nitrogen level was above the critical value (2.1% of dry weight). In the second phase, when nitrogen content decreased from 2.1% to 1.3% of the subsistent content, the correlation between carbon and nitrogen levels was negative. During the last phase, when the nitrogen content decreased below the subsistent value, carbon accumulation stopped. On the contrary, the photosynthetic activity of sporophytes under optimal conditions was severely suppressed when the nitrogen content fell below the subsistent value. Nitrogen levels above the subsistent value resulted in the linear increase in photosynthetic activity. In addition, the surface-to-volume ratio was correlated to the photosynthetic activity. These results indicate that photosynthetic capacity, carbon content and tissue size are linked to the nitrogen status, thus suggesting that the critical and subsistent nitrogen contents are helpful indicators for elucidating the productivity of sporophytes.
  • MIZUTA Hiroyuki, ICHIKI Shigeo, YAMAMOTO Hirotoshi
    Fishereis Science 63 (5) 721 - 724 0919-9268 1997 [Refereed][Not invited]
     
    Viability of crustose coralline algae was measured using three oxidation-reduction indicators: 2,3,5-triphenyl tetrazolium chloride (TTC), 3-(4,5-dimethyl-tiazolyl-2)-2,5-diphenyl tetrazolium chloride (MTT) and alamar blue. The two tetrazolium salts, TTC and MTT, were reduced to form colored formazan in living corallines, but were not reduced in dead corallines. These formazans were extracted and quantified spectrophotometrically. Bluish violet MTT-formazan could be distinguished easily from red phycoerythrin and was useful for judging the viability of crustose corallines. Alamar blue indicated the viability visually and spectrophotometrically by changing the color of the culture medium. The alamar blue assay did not cause any damage to the growth of crustose corallines, indicating that it is suitable for estimating the viability of an individual plant over time. These results suggested that MTT and alamar blue can be used for rapid and simple assay in ecological and physiological investigations for crustose corallines.
  • MIZUTA Hiroyuki, MAITA Yoshiaki, HASHIMOTO Shinji
    Fisheries Science 62 (2) 161 - 167 0919-9268 1997 [Refereed][Not invited]
     
    The nitrogen transportation within the thallus of Laminaria japonica Areschoug was investigated both in laboratory and field experiments. In the laboratory, it was observed by using N-15 as a tracer that the thallus allocated labelled soluble organic N to the younger basal tissues and labelled ammonium to the mature apical tissues. In addition, the younger basal tissues had a higher NH4+ uptake rate than mature apical tissues, and the assimilation of NH4+ was more active in the mature tissues. These results suggest that this transportation is based on two source-sink relationships. One is the transport of inorganic N from basal to mature tissues for assimilation. Another is the transport of soluble organic N assimilated in mature tissues to basal meristematic tissues for growth. To understand the transportation in the natural environment, tissue removal experiments were conducted during N-rich (Jan-Feb) and N-poor (Apr-May) periods. During N-rich periods, the removal of the apical parts led to a decrease of total soluble N content and an increase of inorganic N content in basal tissues and was associated with reduced growth rate. On the other hand, the removal of the basal part resulted in the reverse phenomenon to the removal of the apical part. Thus, the defined transport mechanism is closely connected with the younger basal tissues and mature apical tissues. It is suggested that the mechanism plays an important role in the growth and survival of the blade in the natural environment. The characteristics of the N transport mechanism are also discussed.
  • H MIZUTA, Y MAITA, K KUWADA
    FISHERIES SCIENCE 60 (6) 763 - 767 0919-9268 1994/12 [Refereed][Not invited]
     
    The nitrogen status in the thallus of Laminaria japonica Areschoug under nitrogen limitation is divided to two phases, slight and serious N-deficient phases. This is done by judging from the quantitative storage levels of the soluble nitrogen in the tissues. The slight N-deficient phase is represented by the consumption of soluble nitrogen compounds in the storage pools. After the exhaustion of the nitrogen storage pools, the nitrogen status changes from a slight N-deficient phase to a serious N-deficient phase. Then catabolism was progressed and NH4+ was accumulated as a catabolite under the serious N-deficient phase. The treatment of L-methionine-DL-sulfoxisimine, an inhibitor of glutamine synthetase (GS), resulted in a considerably higher NH4+ accumulation within the tissue segments rather than non-treatment. This fact suggests the presence of a nitrogen recycling mechanism that the NH4+ produced from catabolic processes is actively re-assimilated by GS in the apical tissues. In the natural environment, the blade length was negatively correlated to an NH4+ content in apical tissues along the thallus during the serious N-deficient phase. This suggests that the nitrogen recycling mechanism may be an important role for survival of the seaweed in the period of N-deficiency in seawater. In addition, this mechanism may be closely related to the erosion of apical tissues that is called ''Suegare'' in Japan. Furthermore, the inducing mechanism of ''Suegare'' is also discussed considering with the nitrogen recycling mechanism in the thallus under the serious N-deficiency.
  • Phytoplankton carbon biomass estimated from the size-fractionated chlorophyll a concentration and cell density in the northern coastal waters from spring bloom to summer.
    Odate, T, Yanada, M, Mizuta, H, Maita, Y
    Bull. Plankton Soc. Japan 39 127 - 144 1993 [Refereed]
  • H MIZUTA, Y MAITA, M YANADA
    NIPPON SUISAN GAKKAISHI 日本水産學會 58 (12) 2345 - 2350 0021-5392 1992/12 [Refereed][Not invited]
     
    The seasonal changes of nitrogen metabolism in the sporophyte of Laminaria japonica (Phaeophyceae) were investigated under a natural environment. The experiment was conventionally distinguished by concentrations of nitrogen compounds dissolved in seawater, that is, a relatively high NO2-+NO3- concentration period and a low one. In the high-nitrogen period, the prominent nitrogen metabolism was nitrogen uptake, assimilation, and accumulation. After the ambient nitrite+nitrate was exhausted from the seawater, the nitrogen metabolism was displaced to the utilization of the stored nitrogen. When the nitrogen limitation in the blade was severe about two months after entering the low-nitrogen period, the metabolism was characterized by the utilization of catabolite NH4+ in apical blade tissues. It was suggested from these results that the nitrogen metabolism was divided into three periods: (i) nitrogen uptake and assimilation, (ii) the utilization of stored nitrogen, and (iii) catabolic and re-assimilation periods, with the change in the nitrogen environment. Furthermore, the critical nitrogen content for maintaining maximum growth and the subsistent nitrogen content were 2.4 and 1.3% (on a dry weight basis), respectively. It is suggested that these nitrogen contents are useful for predicting the nitrogen status of the blade and for the effective management of L. japonica cultivation.
  • Mizuta Hiroyuki, Maita Yoshiaki
    Bulletin of the Faculty of Fisheries, Hokkaido University 北海道大学 42 (3) 107 - 114 0018-3458 1991/08 [Not refereed][Not invited]
  • Yoshiaki Maita, Hiroyuki Mizuta, Mitsuru Yanada
    Bull. Fac. Fish. Hokkaido Univ. 42 98 - 106 1991 [Not refereed][Not invited]

MISC

Presentations

Association Memberships

  • THE JAPANESE SOCIETY OF APPLIED PHYCOLOGY   JAPANESE SOCIETY FOR AQUACULTURE SCIENCE   THE JAPANESE SOCIETY OF PHYCOLOGY   THE JAPANESE SOCIETY OF FISHERIES SCIENCE   

Research Projects

  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2020/04 -2023/03 
    Author : 水田 浩之
     
    コンブ胞子体（巨視的世代）は、ストレスを受けると活性酸素を生産し様々な防御機構を誘導することが知られている。その一つとして、胞子体にはオキシダティブバーストによって誘導されるケイ素の細胞外取り込み機構が存在し、この機構が微小世代である配偶体にも備わっていることが示唆された。ケイ素の細胞外取り込み機構は、過酸化水素とハロペルオキシダーゼの存在下でポリフェノールとケイ素が架橋形成することで細胞壁の強化を図っているものと考えられ、配偶体のストレス防御機構の一端が明らかになった。 また、配偶体が他の藻類の下草等として生存・越年する状況を想定し、配偶体を5℃、遮光下で、培地の交換をせずに1～16カ月保存培養し、生残率を測定した。その後保存配偶体を10℃、白色光下（5-10 μmol photons m-2 s-1, 12hr明暗周期）で培養し、成長・成熟過程を観察した。さらに配偶体のクロロフィル蛍光パラメーター（Fv/Fm、Y(Ⅱ)、rETR、NPQ）を、パルス変調クロロフィル蛍光測定装置を用いて測定した。その結果、1‐3カ月間保存した配偶体は保存前と同様の細胞観を呈し、80%以上の生残率と一定のFv/FmとNPQ値を維持し、正常に成長・成熟する能力を有することが明らかになった。6カ月および9カ月間保存した配偶体の平均生残率はそれぞれ68.4%、40.0％に低下し、9カ月の保存配偶体のFv/Fmは保存前の約70%の値に、NPQは約50%の値に低下した。Fv/FmとNPQはマコンブ配偶体の生残率と有意な相関性が認められたことから、長期保存したマコンブ種苗等の生残性を評価する上でFv/FmとNPQが有効な指標となることが明らかになった。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2013 -2015 
    Author : Mizuta Hiroyuki
     
    We tried to search the effective conditions to induce the wounding-resistance in the kelp, particularly Saccharina japonica sporophyte. As a result, it has been found that the irradiation of monochromatic red light induces the hardening in the young sporophytes. In addition, the monochromatic red light irradiation resulted in the increase of lignin-like substance content. The lignin-like compounds and high peroxidase activity were histochemically detected in the cell wall and the adjacent apoplast, particularly of the epidermal cells. Moreover, the monochromatic red light irradiation induced the production of radical oxygen species, which play an important role for the defense mechanism. These observations suggest that red light irradiation functions for the young sporophytes to give the wounding-resistance by hardening of the epidermal cell wall with the deposition of lignin-like substances catalyzed by hydrogen peroxide and peroxidase.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2010 -2012 
    Author : MIZUTA Hiroyuki
     
    We focused on the role of constitutive resistance in the reproduction of kelp, particularly Saccharina japonica. It has been suggested that sori (reproductive organ in the sporophyte) have a high phenolic compound content and that they are protected by the release of iodine and radical oxygen species to combat biotic stresses. Silicon deposition is also considered to provide constitutive resistance in kelp sori. These phenomena suggest that wound-healing and kelp reproduction are supported by both constitutive and induced resistance mechanisms, and that silicon and phenolics deposition might contribute as protectants to the success of kelp reproduction.
  • Ministry of Education, Culture, Sports, Science and Technology：Grants-in-Aid for Scientific Research(基盤研究(C))
    Date (from‐to) : 2004 -2006 
    Author : Hiroyuki MIZUTA
     
    Callus induction and rapid callus propagation in Laminariales plants, which are industrially and ecologically important seaweeds, cannot yet be applied for practical use to select and propagation of desired strain. There is a lack of knowledge regarding the physiological mechanism of callus induction and its growth. In this study, we examined the optimal conditions of callus induction and growth of Laminaria japonica sporophyte and discussed the physiological status of callus. The obtained results are summarized as described below.1.The optimal water temperature and salinity were 10℃ and more than 27.5 psu, respectively, which was similar to that of a whole plant.2.Nutrient-poor conditions decreased the induction rate of callus, and then the growth was stopped. In addition, vitamins were not effective to promote the callus induction.3.Three chelating substances including EDTA, EGTA, and NTA, slightly promoted callus induction or did not affect the induction. However, enrichment of nutrients with chelating substances resulted into the decrease the induction rate of callus.4.The callus induction occurred even in the dark, but the growth gradually decreased. The callus induction rate was significantly higher under red light compared with those under white and blue lights. Inversely, sorus formation was promoted by the irradiation of blue light, and was inhibited under red light.5.The addition of auxin and cytokinins to the culture medium promoted callus formation. It is suggested from microscopic observations that auxin plays an important role for cell division and the elongation, and cytokinins is effective to inhibit the discoloration. In addition, the difference of callus induction rate among parts along the sporophyte seemed to be due to the content of these plant growth regulators.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : SAGA Naotsune, YASUI Hajime, MIZUTA Hiroyuki, KITADE Yukihiro
     
    New findings obtained by this study are as follows. 1. Screening of highly expressed genes during asexual sporulation through monospores We found eight genes encoding enzymes related to metabolism and unknown genes with gametophytic generation-phase-specific expression pattern by cDNA macroarray and RT-PCR or Northern analysis. The eight nucleotide sequences will appear in the GenBank/EMBL/DDBJ databases with accession numbers AB127044 through AB127051. 2. Development of a new technique for gene expression analysis and internal standard in Porphyra yezoensis (1) We developed a method for whole-mount in situ hybridization (WISH) by using elongation factor-1α (EF-1α) riboprobes and gametophytic germlings. (2) We developed an internal standard (actin-related protein 4 homologue) in gene expression analyses of differentially expressed genes. A putative bipartite nuclear localization signal (NLS) and an actin motif were found within the PyARP4 amino acid sequences. The expression level of PyARP4 did not change significantly among four developmental stages of the life cycle and was lower than that of a conventional actin. 3. Induction of monospore production by chemical treatment We found that monospore-like cells with germinability can be obtained when vegetative gametophytic thalli of P.yezoensis were grown in enriched seawater medium that contained 10 mM allantoin. We also found that this chemical treatment is effective to even gametophytic thalli of P.pseudolinearis, which does not have asexual sporulation through monospores in the life cycle.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2003 -2005 
    Author : MONTANI Shigeru, KUDO Isao, MIZUTA Hiroyuki, TADA Kuninao, YANAGI Tetsuo, TSUTSUMI Hiroaki
     
    It is the basic producing process in the tidal flat region where an inclusive finding had been extremely limited up to now though it is assumed most that the animal for each unit area production is a high place on the earth in this research according to various bottlenecks in the research. It was executed to assume a detailed, long-term surveillance study to be a base about Dynamics of the food web following it, to advance the quantification of various sources about Ca, and to execute construction of the ecosystem model in a necessity and an indispensable tidal flat region to the environmental protection in the future at the same time planning. It is impossible to construct a general modeling of the tidal flat group scattered in an environmental place where which it is long and slender and the temperature environment etc. are greatly different only with the observation example in the tidal flat in one place in the south north like our country. Then, our research team selected a typical tidal flat in three places from Hokkaido to Kyushu, obtained this quality and the same kind of observation and the experiment result in each place, aimed at the added role in the living thing of parents element movement of the benthos with a scarce finding so far, and it aimed to construct an inclusive ecosystem model who included it from the primary manufacturing to higher-order production that became the first case in quantification and our country. Basic production of the bottom life diatom was able to be estimated accurately by the research executed in the mouth of a river tidal flat in Takamatsu. Moreover, it was clarified that the level was a value that exceeded basic production in seawater the Inland Sea. In addition, the relation between a benthic animal and an environmental factor was understood in detail. As a result, the amount of the living thing and the composition influenced the living thing by an environmental factor, and it was clarified that the living thing oneself was regenerating the environment oppositely. Finally, it succeeded in making an inclusive ecosystem model in the tidal flat region.
  • 文部科学省：科学研究費補助金(奨励研究(A))
    Date (from‐to) : 1997 -1998 
    Author : 水田 浩之
     
    マコンブLaminaria japonica胞子体片を用いて培養条件下で成熟誘導を試みた。また、自然環境下での子嚢斑形成状況と比較検討した結果、以下のことが明らかになった。1. 胞子体片を用いてた培養で子嚢斑形成が可能となった。2. 子嚢斑形成は15℃で最も早く、かつ大きな子嚢斑を形成した。3. 子嚢斑面積は高光量ほど大きかったが、その形成時期は光量に左右されにくかった。4. 短日条件下での子嚢斑形成は、等日および長日条件下に比べ早かった。5. 貧栄養条件は胞子体片の子嚢斑形成を遅らせかつ、その面積を著しく制限した。6. 子嚢斑形成には、ある一定以上の栄養元素の蓄積が必要であることが示唆された。7. 胞子体基部に比べ先端部の胞子体片の方が子嚢斑形成が早く、また中帯部に比べ縁辺部の方が容易に子嚢斑を形成する傾向が見られた。8. 自然環境下での子嚢斑形成は縁辺部に先立ち中帯部から形成される場合が多かった。9. 視覚的な子嚢斑形成以前に既に胞子体片内では種々の変化生じており、その変化は光合成の低下、呼吸の増加、タンパク質合成に特徴づけられる。10. ホソメコンブ、ガゴメ、アナメ胞子体片でも子嚢斑を形成させることができた。以上の結果から、一年中を通して個体やその採取部位によらず胞子体片を培養することにより子嚢斑を形成させることが可能であることが示された。この胞子体片を用いたマコンブは他のコンブ属植物にも応用でき、採苗方法は時期に左右されずに付着生物等の影響の少ない種苗を提供し得る可能性を示すものである。

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