Study On Phosphorylation Of Thylakoid Protein In Vivo

Protein Phosphorylation is recognized to be a ubiquitous regulatory mechanism. The major function of the thylakoid membranes is to carry out photosynthetic electron transport and ATP synthesis. Several proteins of the thylakoid membranes can be phosphorylated. These phospho proteins include the light-harvesting chlorophyll a/b-binding protein (LHCII and CP29), four PSII core proteins (Dl and D2 reaction center proteins, chlorophyll a-binding protein CP43, and the psbH gene product). The study on physiological roles of the thylakoid phospho protein has received a great deal of attentionWe introduced an immunological approach using INDIA?phosphoprotein probe and Dl, D2, CP43 and LHCII antibody for the analysis of protein phosphorylation in vivo. This new analytical method is more suitable comparing with experiment with [32P] and phosphothreonine antibody.Take advantage of this new analytical tool, the PSII core protein and LHCII in the pea thylakoid were founded to have a different phosphorylation pattern in vivo. Accumulation of the photosystem II core phosphoproteins (Dl, D2) occurred with increasing irradiance, but maximal phosphorylation of LHCII only occurred at low light intensities and drastically decreased at high irradiance. Maximal phosphorylation of CP43 is found in thylakoids isolated from dark-adapted leaves. We used absorption spectroscopy and fluorescence spectroscopy to analyze our result. We proposed that the function established for reversible phosphorylation of PSII core proteins, including Dl and D2, is theprotection of PSII against photoinbibition. The physiological significance for phosphorylation of LHCII is implicated in the regulation of excitation energy distribution between PSII and PSI.We carried out a comparative study on thylakoid membrane phosphoprotein between a new oilseed rape (brassica napus) mutant Cr3529 and its wild type 3529 illuminated at 400 u mol-m-2-s-l. The result of the study indicated that phosphorylation of D1, D2 in the thylakoids of wild type isolated from illuminated leaves increased. Phosphorylation of Dl, D2 decreased in the thylakoids of mutant leaves isolated from illuminated leaves. Maximal phosphorylated and unphosphorylated CP43 of these two types is founded in the thylakoids of leaves isolated from dark-adapted leaves. Phosphorylation of LHCII increase under illuminated condition. So irradiance has a more great influence on the mutant.