Heber U, Walker D
Julius-von-Sachs Institute of Biosciences, University of Würzburg, D-87 Würzburg, Germany.
Plant Physiol. 1992 Dec;100(4):1621-6. doi: 10.1104/pp.100.4.1621.
Coupled cyclic electron transport is assigned a role in the protection of leaves against photoinhibition in addition to its role in ATP synthesis. In leaves, as in reconstituted thylakoid systems, cyclic electron transport requires "poising," i.e. availability of electrons at the reducing side of photosystem I (PSI) and the presence of some oxidized plastoquinone between photosystem II (PSII) and PSI. Under self-regulatory poising conditions that are established when carbon dioxide limits photosynthesis at high light intensities, and particularly when stomata are partially or fully closed as a result of water stress, coupled cyclic electron transport controls linear electron transport by helping to establish a proton gradient large enough to decrease PSII activity and electron flow to PSI. This brings electron donation by PSII, and electron consumption by available electron acceptors, into a balance in which PSI becomes more oxidized than it is during fast carbon assimilation. Avoidance of overreduction of the electron transport chain is a prerequisite for the efficient protection of the photosynthetic apparatus against photoinactivation.
除了在ATP合成中的作用外，偶联循环电子传递在保护叶片免受光抑制方面也发挥着作用。在叶片中，如同在重组类囊体系统中一样，循环电子传递需要“平衡”，即在光系统I（PSI）的还原侧有电子供应，并且在光系统II（PSII）和PSI之间存在一些氧化态的质体醌。在二氧化碳限制高光强下的光合作用时，特别是由于水分胁迫导致气孔部分或完全关闭时所建立的自我调节平衡条件下，偶联循环电子传递通过帮助建立足够大的质子梯度来降低PSII活性和向PSI的电子流，从而控制线性电子传递。这使得PSII的电子供体和可用电子受体的电子消耗达到平衡，在这种平衡中，PSI比快速碳同化过程中更加氧化。避免电子传递链过度还原是有效保护光合机构免受过光灭活的先决条件。
