Abstract: The glutathione-ascorbate cycle and photoinhibition in rice (Oryza sativa cv. Xiangaiyou)leaves under the field condition or with photoinhibitory treatment were examined. The results shown that in clear day in summer, photosynthetic CO₂ fixation rate in rice leaves was depressed at noon (termed as "midday depression") and was partially reversed in the afternoon. Apparent quantum requirement in rice leaves increased largely at noon in a clear day, indicating "midday depression"was related to photoinhibition. Glutathione content in rice leaves was raised from ca 150 nmol·g^-1FW in the morning to ca 300 nmol·g^-1FW at noon in a clear day. More particularly, a nearly two-fold increase in glutathione reductase activity was detected. Ascorbate content as well as dehydroascorbate reductase and ascorbate peroxidase activities remained relatively constant during the whole day. It was also found within 30 min of photoinhibitory treatment, glutathione content and glutathione reductase activity increased respectively about 40% and 70%, whereas no obvious increase both in ascorbate content and in dehydroascorbate reductase and ascorbate peroxidase activities was monitored. Furthermore, a rapid responses of glutathione-ascorbate cycle, characterized by dramatic increase of glutathione content and glutathione reductase activity, to aminotriazole was observed. It was concluded that glutathione content and glutathione reductase activity are the limiting factors for stimulated glutathione-ascorbate cycle, which is probably important for C₃ plants to alleviate photoinhibition.

Key words: Glutathioe-ascorbate cycle, Photoinhibition

摘要： 以水稻品种献改优为材料分析了大田及人工光抑制条件下水稻叶片光抑制表现及谷胱甘肽-抗坏血酸循环系统(以下称谷-抗系统)运转状况。结果显示，在夏季典型晴田，午间水稻叶片光合作用表现出较明显的“午休”现象，阴天“午休”现象消失。表观量子效率分析表明“午休”现象与叶片光抑制有关，晴天水稻叶片谷-抗系统运转速率随日照强度增加而迅速加快，主要表现为谷胱甘肽总量以及谷胱甘肽还原酶活性的明显增加。而GSH／GSSG、抗坏血酸总量以及脱氢抗坏血酸还原酶、抗坏血酸过氧化物酶活性均相对稳定，表明谷-抗系统的运行速率主要受谷胱甘肽含量及谷胱甘肽还原酶活性限制。无CO₂，空气、强光及过氧化氧酶抑制剂处理等试验结果证明谷-抗系统运行对于光合机构清除H₂O₂等有毒街质，减轻损伤具有积极意义。还就水稻叶片的光抑制，谷-抗系统的运行活性与水稻生产的可能联系进行了讨论。

关键词: 光合作用, 光抑制