College of Animal Science & Technology, North-West Agriculture and Forestry University, Yangling, 712100, Shaanxi, China.
Photosynth Res. 2012 Sep;113(1-3):157-64. doi: 10.1007/s11120-012-9743-8. Epub 2012 May 27.
Since photosystem II (PS II) performs the demanding function of water oxidation using light energy, it is susceptible to photoinactivation during photosynthesis. The time course of photoinactivation of PS II yields useful information about the process. Depending on how PS II function is assayed, however, the time course seems to differ. Here, we revisit this problem by using two additional assays: (1) the quantum yield of oxygen evolution in limiting, continuous light and (2) the flash-induced cumulative delivery of PS II electrons to the oxidized primary donor (P700(+)) in PS I measured as a 'P700 kinetics area'. The P700 kinetics area is based on the fact that the two photosystems function in series: when P700 is completely photo-oxidized by a flash added to continuous far-red light, electrons delivered from PS II to PS I by the flash tend to re-reduce P700(+) transiently to an extent depending on the PS II functionality, while the far-red light photo-oxidizes P700 back to the steady-state concentration. The quantum yield of oxygen evolution in limiting, continuous light indeed decreased in a way that deviated from a single-negative exponential. However, measurement of the quantum yield of oxygen in limiting light may be complicated by changes in mitochondrial respiration between darkness and limiting light. Similarly, an assay based on chlorophyll fluorescence may be complicated by the varying depth in leaf tissue from which the signal is detected after progressive photoinactivation of PS II. On the other hand, the P700 kinetics area appears to be a reasonable assay, which is a measure of functional PS II in the whole leaf tissue and independent of changes in mitochondrial respiration. The P700 kinetics area decreased in a single-negative exponential fashion during progressive photoinactivation of PS II in a number of plant species, at least at functional PS II contents ≥6 % of the initial value, in agreement with the conclusion of Sarvikas et al. (Photosynth Res 103:7-17, 2010). That is, the single-negative-exponential time course does not provide evidence for photoprotection of functional PS II complexes by photoinactivated, connected neighbours.
由于光系统 II（PS II）利用光能执行艰巨的水氧化功能，因此它在光合作用过程中容易光失活。 PS II 光失活的时间过程提供了有关该过程的有用信息。 然而，根据 PS II 功能的测定方式，时间过程似乎有所不同。 在这里，我们通过使用另外两种测定方法来重新研究这个问题：（1）在限制的连续光下氧释放的量子产率，以及（2）在 PS I 中测量的作为“ P700 动力学面积”的连续远红光下的光诱导 PS II 电子向氧化的初级供体（P700（+））的累积传递。 P700 动力学面积基于这样一个事实，即两个光系统串联工作：当 P700 被添加到连续远红光中的闪光完全光氧化时，由闪光从 PS II 传递到 PS I 的电子会暂时重新还原 P700（+），程度取决于 PS II 的功能，而远红光将 P700 光氧化回稳定状态浓度。 在限制的连续光下，氧释放的量子产率确实以偏离单一负指数的方式下降。 然而，在黑暗和限制光之间，线粒体呼吸的变化可能会使限制光下氧的量子产率的测量变得复杂。 同样，基于叶绿素荧光的测定也可能因 PS II 逐渐失活后从叶片组织中检测到信号的深度不同而变得复杂。 另一方面，P700 动力学面积似乎是一种合理的测定方法，它是整个叶片组织中功能 PS II 的度量，并且与线粒体呼吸的变化无关。 在许多植物物种中，至少在功能 PS II 含量≥初始值的 6％时，PS II 逐渐失活时，P700 动力学面积以单一负指数方式下降，与 Sarvikas 等人的结论一致（ Photosynth Res 103:7-17, 2010）。 也就是说，单一负指数时间过程并不能为功能 PS II 复合物通过光失活的相邻复合物提供光保护提供证据。
