Lipid peroxide-derived aldehydes produced in plants under various environmental stresses are potentially cytotoxic. Production of aldehydes inside chloroplasts can inhibit photosynthesis, in particular, at the Calvin cycle. Because the reactivity of aldehydes depends on their structure, it is important to determine the chemical species occurring in chloroplasts and their contents. In this study, we analyzed profile of aldehydes in spinach chloroplasts. LC/MS analysis showed that chloroplasts without stress treatments contained the following aldehydes at 10-600 μM; (i) C6-aldehydes (3Z)-hexenal, (2E)-hexenal and n-hexanal, (ii) α,β-unsaturated aldehydes such as crotonaldehyde and 4-hydroxy-2E-hexenal, (iii) short chain aldehydes formaldehyde, propionaldehyde and acetaldehyde and (iv) supposedly several oxo-fatty acids. Because these aldehydes were mainly distributed to thylakoids, their concentrations can reach mM levels in the membrane. In model experiments, it was found that formaldehyde, propionaldehyde, crotonaldehyde, butyraldehyde, (3Z)-hexenal, 4-hydroxy-2E-nonenal are produced from linolenic acid via its oxidation by singlet oxygen.
Glutathione (GSH) is involved in many aspects of plant growth and development including redox control, storage and transport of reduced sulfur, and response to biotic and abiotic stresses. The transport and compartmentalization of GSH is essential to perform all these functions. We have cloned an Iron (Fe) deficiency regulated GSH transporter (IGT) from rice. IGT is a putative member of oligopeptide transporters (OPT) family, and was identified through microarray analysis as its expression was highly upregulated in response to Fe-deficiency. IGT showed high homology i.e. 82% homology to BjGT1 and 80% homology to AtOPT3. Electrophysiological measurements using Xenopus leavis oocytes showed that IGT is a functional GSH transporter. Northern blot analysis and IGT promoter-GUS analysis confirmed that its expression is induced in response to Fe-deficiency in root as well as in shoot tissue. These results suggested that IGT plays a critical role in mitigating Fe-deficiency induced stress in rice.
A transgenic European pear (#32) overexpressing apple spermidine synthase (SPDS) and wild type were subjected to the stress for CdCl2, PbCl2, ZnCl2 or their combination. Based on the shoot growth, #32 was much better than wild type. SPDS expression and Spd titer in #32 were higher than those in wild type. Glutathione was significantly depleted in line #32 with stress, but not so much in wild type. Activities of glutathione reductase/superoxide dismutase and malondialdehyde content were changed under stress toward a more favorable direction for survival in #32: these changes were closely related to the Spd titer. Accumulation of heavy metals tended to be less in #32 than that in wild type except for ZnCl2 stress, while calcium content showed the reverse trend. Therefore, Spd levels are implicated in enhanced heavy metal tolerance possibly via the antioxidant property of Spd per se as well as by exerting an antioxidant system.
植物は根圏環境の低リン状態に対して様々な戦略をもって適応していることが知られている。本研究は、イネ科、アブラナ科、マメ科といった低リン適応にそれぞれ特色のある科のモデル植物であるイネ、シロイヌナズナ、ミヤコグサを用いて、低リン適応戦略を解析することを目的とした。幼植物時に水耕栽培において低リン処理した場合の植物の代謝変動を、リン充足条件で栽培した植物と比較により解析した。トランスクリプトーム解析を地上部と根部に対して行ない、その結果を基に可能な限りKappa-Viewによるパスウェイ解析を行った。さらにリン代謝において重要と判断されたいくつかの遺伝子に関してはReal time PCRによる発現量解析を行い、培養液および体内のリンレベルに対しての変動を調べた。3種の植物に概ね共通して、酸性ホスファターゼやヌクレアーゼ、解糖系、デンプン合成系の遺伝子などが、地上部、根部ともにリン欠乏で発現が増加した。炭素代謝においては、TCAサイクルやグリオキシル酸回路などでのリン欠乏応答の違いが植物間で顕著であった。また、種間でのリン欠乏による遺伝子発現応答の違いは、二次代謝産物関連遺伝子において最も顕著だった。特にフラボノイド代謝系においてそれぞれの植物種で特徴的な傾向が判断されたことから、本発表ではLC-MS/MSを用いたいくつかのフラボノイドの定量解析結果も報告する。