University of the Ryukyus · Graduate School of Science and Engineering · 教授

Research keywords環境生物学・活性酸素・ストレス生理学・光合成・活性硫黄・活性窒素

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• Seawater Tolerance of the Beach Bean Vigna marina (Burm.) Merrill in Comparison with Mung Bean (Vigna radiata) and Adzuki Bean (Vigna angularis)2025 · Seawater intrusion into soils caused by global climate change and tsunami disasters is a significant factor contributing to soil salinization in coastal vegetation areas, posing a critical threat to agriculture and food security. This study aimed to evaluate the seawater tolerance of Vigna marina, a wild Vigna species, through comparative laboratory experiments with Vigna radiata (mung bean) and Vigna angularis (adzuki bean). Unlike V. radiata and V. angularis, the seeds of V. marina exhibited significant buoyancy in seawater, remaining afloat for at least 30 days. After this prolonged seawater incubation, V. marina seeds maintained a 100% germination rate, whereas V. radiata and V. angularis failed to germinate under the same conditions. The photosynthetic activity of V. marina seedlings, evaluated via the Fv/Fm parameter, remained stable even after seven days of seawater irrigation. In contrast, V. radiata and V. angularis perished under seawater irrigation. Furthermore, V. marina seedlings exhibited sustained growth under seawater irrigation, showing consistent increases in both fresh and dry weight. These findings confirm that V. marina possesses remarkable tolerance to seawater, a critical characteristic for cultivation in areas affected by seawater intrusion.
• Spatiotemporal Characteristics Determining the Multifaceted Nature of Reactive Oxygen, Nitrogen, and Sulfur Species in Relation to Proton Homeostasis2025 · Yamasaki, H; Itoh, RD; Mizumoto, KB; Yoshida, YS; Otaki, JM; Cohen, MF
• Phytochemical Antioxidants: Past, Present and Future2021 · Most diseases that are difficult to prevent and cure are “syndromes” that are governed by multiple components with complicated interactions. Whatever the cause of such diseases, overproduction of harmful reactive oxygen species (ROS) can often be observed in progression of the disease. Under such conditions, the cells may be challenged by “oxidative stress” due to excessively generated oxidants. Antioxidants can be defined as chemical compounds that scavenge ROS or free radicals over-produced in the cells under oxidative stress conditions. The plant pigments flavonoids and betalains, rich in fruits and vegetables, are reactive not only with ROS but also with reactive nitrogen species (RNS) and possibly with reactive sulfur species (RSS). Here, we provide an overview of updates on the antioxidative functions of the plant pigments along with some prospects for future research on phytochemical antioxidants.
• Pleiotropic Functions of Nitric Oxide Produced by Ascorbate for the Prevention and Mitigation of COVID-19: A Revaluation of Pauling's Vitamin C Therapy.2019 · Linus Pauling, who was awarded the Nobel Prize in Chemistry, suggested that a high dose of vitamin C (L-ascorbic acid) might work as a prevention or treatment for the common cold. Vitamin C therapy was tested in clinical trials, but clear evidence was not found at that time. Although Pauling’s proposal has been strongly criticized for a long time, vitamin C therapy has continued to be tested as a treatment for a variety of diseases, including coronavirus infectious disease 2019 (COVID-19). The pathogen of COVID-19, SARS-CoV-2, belongs to the β-coronavirus lineage, which includes human coronavirus, severe acute respiratory syndrome (SARS), and Middle East respiratory syndrome (MERS). This review intends to shed new light on vitamin C antiviral activity that may prevent SARS-CoV-2 infection through the chemical production of nitric oxide (NO). NO is a gaseous free radical that is largely produced by the enzyme NO synthase (NOS) in cells. NO produced by upper epidermal cells contributes to the inactivation of viruses and bacteria contained in air or aerosols. In addition to enzymatic production, NO can be gener-ated by the chemical reduction of inorganic nitrite (NO2−), an alternative mechanism for NO production in living organisms. Dietary vitamin C, largely contained in fruits and vegetables, can reduce the nitrite in saliva to produce NO in the oral cavity when chewing foods. In the stomach, salivary nitrite can also be reduced to NO by vitamin C secreted from the epidermal cells of the stomach. The strong acidic pH of gastric juice facilitates the chemical reduction of salivary nitrite to produce NO. Vitamin C contributes in multiple ways to the host innate immune system as a first-line defense mechanism against pathogens. Highlighting chemical NO production by vitamin C, we suggest that controversies on the therapeutic effects of vitamin C in previous clinical trials may partly be due to less appreciation of the pleiotropic functions of vitamin C as a universal bioreductant.

• D-アミノ酸によるアカウキクサの分離拡散機構2019 · アカウキクサ（#IAzolla#IR）は、水田や池に浮遊している水生シダ植物である。繁殖力の強い外来種は、外来生物法上の特定外来生物に指定されており、大量発生の防止および駆除が国内外での検討課題となっている。アカウキクサは、環境の変化を検知すると、根を自切して分離拡散する特異な生理応答を示す。この特徴的な環境応答がアカウキクサの広域分散を可能にしている。しかし、アカウキクサに見られる根脱離応答機構は不明のままである。本研究では、D-アミノ酸誘導性の根脱離メカニズムを明らかにし、アカウキクサ大量発生抑制技術の開発、および有害アカウキクサ駆除対策の立案に資する生物学的学術基盤の確立を行う。
• 環境変動に伴って増加する造礁サンゴの病変予防技術の基盤研究2015 · 近年、世界各地でサンゴ病変が拡大しており、サンゴ礁生態系衰退の要因として危惧されている。本研究では、ブラックバンド病（BBD）を対象に、サンゴ病変予防技術確立に必要な生物学的基礎知見を得ることを目的とした。調査の結果、沖永良部島、宮古島、台湾緑島の広域でBBD発症サンゴが確認され、被覆状コモンサンゴの高率罹患が沖縄近海で認められた。沖縄で見られるBBDに関与するシアノバクテリアとして、#IRoseofilum reptotaenium#IRを同定し、他にも数多くの未記載種の存在が確認された。BBDの治癒を促す各種処理を検討した結果、連続暗黒処理が現時点で最も有効な手段である事が明らかになった。
• サンゴ礁における海水富栄養化の慢性毒性評価法の確立2011 · 本研究課題では、海水の富栄養化によってサンゴが受ける「慢性ストレス」の評価技術の確立を目的として、生化学的な新規定量法の開発を試みた。「活性酸素」と良く似た性質を持つ「活性窒素」の生成と消去のバランス崩壊が、ヒトの慢性ストレス障害に関与していることが指摘されている。そこで、富栄養化に伴う活性窒素障害（窒素毒性）の生化学的痕跡として生体成分のニトロ化に着目し、普及を念頭においた簡便技術の開発を検討した。ニトロ化合物を酸化分解処理し、遊離してくる硝酸イオンをイオンクロマトフラフィーによって検出することで、ニトロ化レベルが定量化できることが明らかとなった。
• 地下浸透海水を用いたサンゴ白化抑制技術の開発

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