关键词: 光合作用, 光抑制

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