D1 protein phosphorylation/dephosphorylation alone has no effect on the electron transport activity of photosystem II in soybean leaves

In order to explore the relationship between the phosphorylation of D1 protein and the function of PSII reaction center, the changes in chlorophyll fluorescence parameters, PSII electron transport activity and D1 protein amount were observed after dephosphorylation of phosphorylated D1 proteins caused by FSBA (5′- p -fluorosulfonylbenzoyl adenosine, an inhibitor of protein kinase) treatment. Also, phosphorylated and non-phosphorylated D1 proteins (D1* and D1, respectively) were analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and Western Blotting. The following results were obtained. (1) D1* could be up to 74% of the total D1 proteins in dark-adapted soybean leaves and could be completely dephosphorylated by FSBA (1 mM) treatment for 2 h. (2) Dephosphorylation of D1* resulted in neither substantial net loss of D1 proteins nor the significant changes in value of chlorophyll fluorescence parameters. (3) The electron transport activity of PS II (H 2 O→1,4-BQ) was not changed significantly after D1* was completely dephosphorylated. Based on these results, it is concluded that D1 protein phosphorylation/dephosphorylation alone has no significant effect on the function of PS II reaction center in soybean leaves.