Control of chloroplast electron transport by phosphorylation of thylakoid proteins

Several chloroplast membrane proteins can become phosphorylated by a membrane protein kinase. The kinase is activated when the electron carriers (plastoquinone) between photosystem II and photosystem I are reduced. Phosphorylation of the light harvesting complex of photosystem II causes a decrease in energy transferred to photosystem II and increase in the rate of excitation of photosystem I. This process, which is mediated by lateral diffusion of the phosphorylated complex serves to regulate the relative rates of electron transfer through the two photosystems. Phosphorylation may also have an important role in balancing the rate of excitation of photosystem II with the capacity for photosynthetic carbon metabolism and in controlling the functional state of photosystem II.