Elevated temperature treatment induced alteration in thylakoid membrane organization and energy distribution between the two photosystems in Pisum sativum

Two-week-old pea (Pisum sativum var. Arkal) plants were subjected to elevated temperature (38 degreesC/42 degreesC) in dark for 14-15 h. The effect of heat treatment on light- induced phosphorylation of LHCII and LHCII migration in the thylakoid membranes were investigated. The heat treatment did cause a substantial (more than two fold) increase in the extent of LHCII phosphorylation as compared to the control. Upon separation of appressed and non-appressed thylakoid fractions by digitonin treatment, the heat-treated samples showed a decrease in LHCII-related polypeptides from the grana stack (appressed region) over the control. Further, a small increase in the intensity of these (LHCII-related) bands was detected in stromal thylakoid fraction (non-appressed membranes). This suggests an enhanced extent of migration of phosphorylated LHCII from appressed to non-appressed regions due to in vivo heat treatment of pea plants. We also isolated the LHCII from control and heat treated (42 degreesC) pea seedlings. Analysis of CD spectra revealed a 5 - 6 run blue shift in the 638 run negative peak in heat treated samples suggesting alteration in the organization of Chl b in the LHCII macro-aggregates. These results suggest that in vivo heat stress not only alters the extent of migration of LHCII to stromal region, but also affects the light harvesting mechanism by LHCII associated with the grana region.