Control of Chloroplast Electron Transport by Phosphoproteins

The thylakoid protein phosphorylation is suggested to be involved in the redistribution of the excitation energy between photosystem 2 (PS2) and photosystem 1 (PSI) (1) and/or by the change in the primary photoproducts stoichiometry (2, 3). Numerous data were achieved which confirm these hypothesis. However investigations involving the studies of changes of linear and cyclic electron transport rates are rare. Some results are not consistent. Some data reliably suggested that an inhibition of PS2 photoreaction takes place (3–8). Data concerning changes of PSI activity are not numerous and they are not confirmed. Enhancement of NADP and methylviologen (MV) photoreduction was reported (3, 9). There is some evidence about photophosphorylation increase (3, 10). But some authors have reported the absence of PSI activity rise under phosphorylation (11–12). Changes of electron transport rates of whole electron transport chain (ETC) induced by membrane protein phosphorylation were studied in some works and the results were also inconsistent. There are data showing that electron transport of the whole ETC is not changed (10) or it was reduced (6). Jennings and Zucchelli have demonstrated an increase in NADP photoreduction from water in the presence of gramicidin (13). They concluded that oxidised plastoquinone level reached under phosphorylation conditions caused the change of the NADP reduction rate.