Abstract:

Physiological indices related to PSⅡ photochemical efficiency (F_v/F_m) and membrane lipid peroxidation were measured in leaves of indica rice cv Shanyou 63 and japonica rice 9516 at different temperatures and light intensities for four days. No obvious changes in F_v/F_m and MDA were observed in both indica and japonica rice at moderate temperature and medium PFD, implying neither photoinhibition nor photooxidation happened in these cases. In indica rice either at medium temperature with higher PFD or at lower temperature with medium PFD F_v/F_m dropped obviously with no changes in MDA contents, and photoinhibition appeared while photooxidation did not occur. However, D₁ protein, F_v/F_m, (A+Z)/(A+Z+V), and SOD activities dropped, and O₂ production and MDA content increased accordingly, as well as both photoinhibition and photooxidation appeared in two rice varieties at lower temperature and higher PFD. Experiment with inhibitors at lower temperature and higher PFD showed that as compared with japonica rice the decrements appeared in D₁ protein contents, SOD activities, and (A+Z)/(A+Z+V) ratios, the xanthophyll cycle and non-photochemical quench (q_N) were inhibited in a more degree, as well as increments of MDA content were greater, thus exhibiting more distinct photoinhibition and photooxidation in indica rice. It is suggested that F_v/F_m and membrane lipid peroxidation product－MDA were the key indices to predict and diagnose photooxidation.

Key words: D1 protein, photochemical efficiency, membrane lipid peroxidation, xanthophyll cycle, rice