DIURNAL CHANGES OF PHOTOOXIDATION RESPONSE IN LEAVES OF C3 AND C4 PLANTS

Abstract:

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, q_p and PSII were found to have a maximal decrease in maize leaves and a minimal decrease in-peanut leaves at 12: 00. MV-induced q_N 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.