title: The effects of ultraviolet irradiation on P680(+) reduction in PS II core complexes measured for individual S-states and during repetitive cycling of the oxygen-evolving complex.
abstract: Flash-induced absorbance measurements at 830 nm on both nanosecond and microsecond timescales have been used to characterise the effect of ultraviolet light on Photosystem II core particles. A combination of UV-A and UV-B, closely simulating the spectrum of sunlight below 350 nm, was found to have a primary effect on the donor side of P680. Repetitive measurements indicated reductions in the nanosecond components of the absorbance decay with a concomitant appearance and increase in the amplitude of a component with a 10 μs time constant attributed to slow reduction of P680(+) by Tyrz when the function of the oxygen evolving complex is inhibited. Single-flash measurements show that the nanosecond components have amplitudes which vary with S-state. Increasing UV irradiation inhibited the amplitude of these components without changing their S-state dependence. In addition, UV irradiation resulted in a reduction in the total amplitude, with no change in the proportion of the 10 μs contribution.
authors.affiliation: School of Biological Sciences, A12, University of Sydney, 2006, N.S.W., Australia.
authors.forename: A
authors.initials: A
authors.lastname: Post
authors.forename: P B
authors.initials: PB
authors.lastname: Lukins
authors.forename: P J
authors.initials: PJ
authors.lastname: Walker
authors.forename: A W
authors.initials: AW
authors.lastname: Larkum