The Effect of Hydrogen Peroxide on the Redistribution of Antenna Complexes Between Photosystems in Higher Plants.

One of the adaptive mechanisms used by photosynthetic organisms in response to changing light conditions is redistribution of antenna complexes between the photosystems, a process known as state transitions (ST). This mechanism allows to regulate the amount of light energy absorbed by the photosystems. Numerous studies have reported inhibition of ST at the elevated light intensity; however, the mechanism underlying this process is still debated. We evaluated the effect of HO at various concentrations on the ST process in functionally active thylakoids isolated from leaves and investigated which stage of this process is affected by HO. To assess the extent of ST, we measured low-temperature chlorophyll  fluorescence spectra (650-780 nm) and calculated the F745/F685 ratio, whose changes can serve as an indicator of ST progression. HO inhibited ST under the low-intensity light conditions and, furthermore, led to a decrease in the accumulation of phosphorylated Lhcb1 and Lhcb2 proteins involved in ST. This suggests that the observed ST inhibition resulted from the suppression of STN7 kinase activity. Importantly, HO in the tested concentrations did not affect the electron transport rate, indicating that the inhibition of STN7 kinase activity was not associated with suppression of the photosynthetic electron transport chain (PETC) activity. The treatment with HO did not reduce the level of phosphorylated D1 protein (a product of phosphorylation by the thylakoid STN8 kinase). Taken together, these results demonstrate for the first time the mechanism by which HO inhibits STN7 kinase activity and, consequently, the process of ST.