Abstract
The levels and/or redox state of NADP(H) in chloroplasts must be properly regulated, since it is essential not only for primary metabolism including photosynthesis, but also for antioxidative systems. Recently we found that an Arabidopsis chloroplastic Nudix hydrolase, AtNUDX19, has the pyrophosphohydrolase activity toward NADPH and its expression is increased with increasing light intensity. Here, to clarify the involvement of AtNUDX19 in photoacclimation, we isolated and characterized a knockout mutant lacking AtNUDX19 (KO-nudx19).
Under normal and high-light (100 and 800 μmol/m2/s, respectively) conditions, levels of NADPH were higher in the KO-nudx19 than in the wild-type plants, while levels of NADP+ were lower in the mutants. Interestingly, the initial activities of enzymes in the Calvin cycle, and the activities of CO2 fixation and photosynthetic electron transport were increased in the KO-nudx19 under high-light, resulting in enhanced growth of the mutants. Moreover, the activities of antioxidative enzymes were increased in the KO-nudx19. These findings suggest that AtNUDX19 acts as a crucial regulator for photoacclimation.
