C_3和C_4植物叶片对光氧化响应的日变化

DIURNAL CHANGES OF PHOTOOXIDATION RESPONSE IN LEAVES OF C_3 AND C_4 PLANTS

田间生长的C3植物花生和C4植物玉米分别于晴天上午9：00、中午12：00、下午15：00取样。中午12：00花生叶片的Fv／Fm较早上9：见下降16％，出现了光抑制现象，玉米叶片的Fv／Fm则未下降。不同时间取样的花生和玉米叶片经甲基紫精（MV）+强光的人为光氧化处理，叶绿素和类胡萝卜素出现不同程度的氧化降解，中午12：00降解幅度最大，15时降幅最小。植物叶片的抗氧化能力与其SOD活性相关，而与PEPCase的活性没有明显的相关性。光氧化处理后，花生和玉米的叶绿素荧光参数FV／Fm、qp、pSII都下降，花生在12：00的降幅最小，玉米的降幅最大。光氧化引起花生的qN和热耗散系数（KD）上升，玉米则都下降．结果显示C3植物花生和C4植物玉米对光氧化的响应可能存在不同的机制。

Diurnal changes of SOD, POD and PEPCase activities, pigment contents and chlorophyll fluorescence parameters were compared between C3 plant peanut (Arachis hypogaea) and C4 plant maize (Zea mays) under natural condition and photooxidation condition. Plant leaves were collected at g:00(a.m.), 12:00(noon) and 15t00(p.m.) in the field during a day, respectively, and then treated by 500 umol/L methyl viologen (MV) under 1500 umol m-2s-1 light intensity for 30 min. In the midday (12: 00), Fv/Fm in untreated peanut leaves decreased by 16% indicating that the photoinhibition occured, while that in untreated maize leaves showed no change. After MV-photooxidation treatment, the maximal decrease in chlorophyll and carotenoid were found in both peanut and maize leaves at 12:00. The antioxidative ability was related to SOD activity but seemed not to be related to PEPCase activity. Under MV-photooxidation, Fv/Fm, qp and PSII were found to have a maximal decrease in maize leaves and a minimal decrease in-peanut leaves at 12: 00. MV-induced qN and KD (coefficient of heat dissipation) were increased in peanut leaves but decreased in maize leaves during a day. It is proposed that a different mechanism in response to photooxidation may exist between C3 plant and C4plant.