Photo-inhibition and the Effects of Protein Phosphorylation on Electron Transport in Wheat Thylakoids

Publisher Website
Google Scholar
Abstract
The kinetics of changes in photosystem I (PSI), photosystem II (PSII), and whole chain (PSII and PSI) electron transport, chlorophyll fluorescence parameters, the capacity to bind atrazine and the polypeptide profiles of thylakoids isolated from wheat leaves on exposure to a photon flux density of 2000 μmol m−2 s−1 were determined. Severe and similar levels of photo-inhibitory damage to both PSII and whole chain electron transport occurred and were correlated with decreases in the ratio of variable to maximal fluorescence, the proportional contribution of the rapid a phase of the fluorescence kinetics and the capacity to bind atrazine. Severe photo-inhibition of electron transport was not associated with a major loss of chlorophyll or total thylakoid protein. However, a small decrease in a 70 kDa polypeptide together with increases in a number of low molecular mass polypeptides (8–24 kDa) occurred. Phosphorylation of thylakoid polypeptides alleviated photo-inhibition of PSII electron transport but stimulated photoinhibitory damage to whole chain electron transport. The consequences of such phosphorylation-induced effects on photoinhibition in vivo are considered.