Abstract
Chloroplasts have many defense systems against excess light. Some of these systems involve the reactions with mitochondria. Although excess reducing equivalents generated in chloroplasts can be exported to mitochondria, detailed mechanisms in intact leaves are not clear. In our prevent study, it was suggested that the mitochondrial alternative oxidase (AOX) has essential roles in dissipation of excess reducing equivalents (Yoshida et al. 2006). To conclude this probability, we analyze the respiratory properties in the leaves under the excess light. We used Arabidopsis thaliana mutants which lack the major defense systems in chloroplasts, the cyclic electron transport around PSI and D1 protein turnover. When exposed in high light, the leaves in the mutants showed photoinhibition more than wild type and higher rates of KCN-resistant respiration. These results suggest that AOX would function as a sink of excess reducing equivalents and contribute the mitigation of photoinhibition.
