UVB and UVB/white-light-induced inhibition of thylakoid electron transfer reactions studied by fluorescence induction and fluorescence decay: Damage to donor and acceptor side components of PSII

Abstract

Approximately 1.5% of the solar radiation reaching the Earth’s surface is accounted for by wavelengths in the ultraviolet-B range (280-320 nm) and its amount is increasing as a consequence of stratospheric ozone depletion linked to human activity. This radiation is known to be harmful to all biological organisms and even a modest increase in its level may induce adverse effects on the biosphere, with plants particularly sensitive. In this study we report new data on the effect of ecologically significant level of UVB light, alone or in combination with visible light, on photosynthetic electron transfer reactions in the stress-tolerant organism Thellungiella salsuginea. We could confirm that UVB light harms the donor side of photosystem II, but also electron transfer beyond the acceptor side of the photosystem (i.e., cytochrome b6/f or photosystem I) is affected. In the presence of background visible light, the effect of UVB is rather different and a main target became electron transfer between QA and QB.