Abstract
Although light is essential for photosynthesis, absorption of excessive light energy causes generation of active oxygen species, leading to irreversible damages of photosynthetic apparatus. Excess of light energy does not simply depend on light intensity but is enhanced by environmental stresses such as low temperature or drought. Plants monitor the excess of light energy by measuring acidification of thylakoid lumen. Since the lumen acidification is also essential for ATP synthesis, it is a complex process to regulate the lumen pH to maximize the efficiency of photosynthesis. We clarified that PSI cyclic electron transport is essential for this regulation. However, a precise mechanism of the regulation and the identity of the molecular machinery have been poorly understood. I discuss the current progress in this field.
