Institut de Biologie Physico-Chimique, Unité Mixte de Recherche 7141, Centre National de la Recherche Scientifique and Université Pierre et Marie Curie-Université Paris 6, 75005 Paris, France.
Proc Natl Acad Sci U S A. 2011 Aug 9;108(32):13317-22. doi: 10.1073/pnas.1110189108. Epub 2011 Jul 22.
Cyclic electron flow is increasingly recognized as being essential in plant growth, generating a pH gradient across thylakoid membrane (ΔpH) that contributes to ATP synthesis and triggers the protective process of nonphotochemical quenching (NPQ) under stress conditions. Here, we report experiments demonstrating the importance of that ΔpH in protecting plants from stress and relating to the regulation of cyclic relative to linear flow. In leaves infiltrated with low concentrations of nigericin, which dissipates the ΔpH without significantly affecting the potential gradient, thereby maintaining ATP synthesis, the extent of NPQ was markedly lower, reflecting the lower ΔpH. At the same time, the photosystem (PS) I primary donor P700 was largely reduced in the light, in contrast to control conditions where increasing light progressively oxidized P700, due to down-regulation of the cytochrome bf complex. Illumination of nigericin-infiltrated leaves resulted in photoinhibition of PSII but also, more markedly, of PSI. Plants lacking ferredoxin (Fd) NADP oxidoreductase (FNR) or the polypeptide proton gradient regulation 5 (PGR5) also show reduction of P700 in the light and increased sensitivity to PSI photoinhibition, demonstrating that the regulation of the cytochrome bf complex (cyt bf) is essential for protection of PSI from light stress. The formation of a ΔpH is concluded to be essential to that regulation, with cyclic electron flow playing a vital, previously poorly appreciated role in this protective process. Examination of cyclic electron flow in plants with a reduced content of FNR shows that these antisense plants are less able to maintain a steady rate of this pathway. This reduction is suggested to reflect a change in the distribution of FNR from cyclic to linear flow, likely reflecting the formation or disassembly of FNR-cytochrome bf complex.
循环电子流在植物生长中越来越被认为是必不可少的，它在类囊体膜上产生 pH 梯度（ΔpH），有助于 ATP 的合成，并在胁迫条件下触发非光化学猝灭（NPQ）的保护过程。在这里，我们报告了一些实验，这些实验证明了ΔpH 在保护植物免受胁迫方面的重要性，并与循环相对于线性流动的调节有关。在叶片中渗透低浓度的 Nigericin，它会耗散ΔpH，而不会显著影响潜在梯度，从而维持 ATP 的合成，NPQ 的程度显著降低，反映了较低的ΔpH。与此同时，在光照下，光系统（PS）I 的初级供体 P700 大量减少，与对照条件形成对比，在对照条件下，随着光照的增加，P700 逐渐被氧化，这是由于细胞色素 bf 复合物的下调。Nigericin 渗透的叶片光照导致 PSII 光抑制，但更显著的是 PSI 光抑制。缺乏铁氧还蛋白（Fd）NADP 氧化还原酶（FNR）或多肽质子梯度调节 5（PGR5）的植物也显示出 P700 在光照下的还原和对 PSI 光抑制的敏感性增加，这表明细胞色素 bf 复合物（cyt bf）的调节对于保护 PSI 免受光胁迫是必不可少的。形成ΔpH 被认为是这种调节的必要条件，循环电子流在这个保护过程中起着至关重要的、以前未被充分认识的作用。在 FNR 含量降低的植物中检查循环电子流表明，这些反义植物不太能够维持该途径的稳定速率。这种减少被认为反映了 FNR 从循环到线性流动的分布变化，可能反映了 FNR-细胞色素 bf 复合物的形成或解体。
