Damage and protection of the photosynthetic apparatus from UV-B radiation. I. Effect of ascorbate.

In this work, the effect of the exogenously added ascorbate (Asc) against the UV-B inhibition of the photosystem II (PSII) functions in isolated pea thylakoid membranes was studied. The results reveal that Asc decreases the UV-B induced damage of the donor and the acceptor side of PSII during short treatment up to 60 min. The exogenous Asc exhibits a different UV-protective effect on PSII centers in grana and stroma lamellae, as the effect is more pronounced on the PSIIβ centers in comparison to PSIIα centers. Data also suggest that one of the possible protective roles of the Asc in photosynthetic membranes is the modification of the oxygen-evolving complex by influence on the initial S(0)-S(1) state distribution in the dark.