D1 protein turnover and carotene synthesis in relation to zeaxanthin epoxidation in rice leaves during recovery from low temperature photoinhibition

The relationship between D1 protein turnover, carotene synthesis and zeaxanthin epoxidation was exam-ined in rice (Oryza sativa L.) leaves during recovery subsequent to chilling treatments at 500 (moderate light) or 1000 mol photons m –2 s –1 (high light) for 3 h. When recovery was monitored in the light, the decrease in the level of zeaxanthin was closely paralleled by the slow increase in the efficiency of photosystem (PS) II. Both these processes were greatly slowed down in the presence of lincomycin, an inhibitor of chloroplast-coded protein synthesis. In leaves chilled in moderate light, the inhibitory effect of lincomycin on zeaxanthin decrease was largely eliminated by infiltration with dithiothreitol, an inhibitor of de-epoxidase, suggesting a stimulation of violaxanthin de-epoxidation rather than an inhibition of zeaxanthin epoxidation in the presence of lincomycin. In high-light-chilled leaves, lincomycin had little impact on violaxanthin de-epoxidation but strikingly blocked the process of zeaxanthin epoxidation. Furthermore both PSII recovery and zeaxanthin epoxidation in high-light-chilled leaves were almost completely suppressed by incubation with either fluridone or norflurazon, two inhibitors of carotene synthesis. The possible reason for parallel changes in the level of zeaxanthin and PSII efficiency during recovery from photoinhibition is discussed.