Larkum A W, Karge M, Reifarth F, Eckert H J, Post A, Renger G
School of Biological Sciences, University of Sydney, NSW, 2006, Australia.
Photosynth Res. 2001;68(1):49-60. doi: 10.1023/A:1011884031354.
The adverse effect of low intensity, small band UV-B irradiation (lambda = 305 +/- 5 nm, I = 300 mW m(-2)) on PS II has been studied by comparative measurements of laser flash-induced changes of the absorption at 325 nm, DeltaA(325)(t), as an indicator of redox changes in Q(A), and of the relative fluorescence quantum yield, F(t)/F(o), in PS II membrane fragments. The properties of untreated control were compared with those of samples where the oxygen evolution rate under illumination with continuous saturating light was inhibited by up to 95%. The following results were obtained: a) the detectable initial amplitude (at a time resolution of 30 mus) of the 325 nm absorption changes, DeltaA(325), remained virtually invariant whereas the relaxation kinetics exhibit significant changes, b) the 300 mus kinetics of DeltaA(325) dominating the relaxation in UV-B treated samples was largely replaced by a 1.3 ms kinetics after addition of MnCl(2), c) the extent of the flash induced rise of the relative fluorescence quantum yield was severely diminished in UV-B treated PS II membrane fragments but the relaxation kinetics remain virtually unaffected. Based on these results the water oxidizing complex (WOC) is inferred to be the primary target of UV-B impairment of PS II while the formation of the 'stable' radical pair P680(+)Q(A) (-) () is almost invariant to this UV-B treatment.
通过比较测量激光闪光诱导的325nm处吸收变化（ΔA(325)(t)）作为Q(A)中氧化还原变化的指标，以及PS II膜片段中相对荧光量子产率F(t)/F(o)，研究了低强度、小波段UV-B辐射（波长λ = 305 ± 5nm，强度I = 300mW m(-2)）对PS II的不利影响。将未处理对照的特性与连续饱和光照下氧气释放速率被抑制高达95%的样品的特性进行了比较。得到以下结果：a）325nm吸收变化的可检测初始幅度（时间分辨率为30μs），即ΔA(325)，实际上保持不变，而弛豫动力学表现出显著变化；b）在UV-B处理样品中主导弛豫的300μs的ΔA(325)动力学在添加MnCl(2)后很大程度上被1.3ms的动力学所取代；c）在UV-B处理的PS II膜片段中，闪光诱导的相对荧光量子产率上升程度严重降低，但弛豫动力学实际上未受影响。基于这些结果，推断水氧化复合物（WOC）是UV-B对PS II造成损伤的主要靶点，而“稳定”自由基对P680(+)Q(A)(-) ()的形成对这种UV-B处理几乎没有变化。
