Changes in phosphorylation status of wheat plastid polypeptides as influenced by light, calcium and cyclic AMP

The polypeptides of etioplast and chloroplast fractions, purified on Percol l discontinuous gradient, were phosphorylated in vitro using (gamma-P-32)AT P, resolved by SDS-PAGE and autoradiographed. In general, about 15-18 phosp hopolypeptides in the range of 14-150 kD were distinctly visible in autorad iograms of both organelle fractions with varying degree of radiolabel incor poration. Although short-term irradiation with red or far-red light did not have any significant effect on phosphorylation status of etioplast polypep tides, in vivo irradiation with 1 h white light, followed by in vitro phosp horylation, decreased phosphorylation of a 116 kD polypeptide and increased the phosphorylation of polypeptides of 38 kD and a doublet around 20 kD. S trikingly, the phosphorylation status of 116 kD etioplast polypeptide was a dversely affected by Ca2+ as well, and this phosphopolypeptide was not dist inctly visible in the autoradiogram of the chloroplast fraction proteins, H owever, in vitro phosphorylation of 98, 57 and 50 kD polypeptides of both e tioplast and chloroplast fractions was found to be Ca2+ dependent. Unlike C a2+, 3',5'-cyclic AMP downregulated the phosphorylation of several polypept ides of both etioplasts and chloroplasts, including 98 and 50 kD, and upreg ulated the phosphorylation of 32 and 57 kD polypeptides. The significance o f these observations on changes in phosphoprotein profile of etioplasts and chloroplasts, as influenced by light, Ca2+ and cyclic nucleotides, has bee n discussed.