Lehrstuhl für Botanik I, der Universität Würzburg, Mittlerer Dallenbergweg 64, D-8700, Wurzburg, Germany.
Photosynth Res. 1993 Sep;37(3):177-91. doi: 10.1007/BF00032822.
This paper examines the effect of inorganic carbon transport and accumulation in Synechococcus PCC7942 on fluorescence quenching, photosynthetic oxygen reduction and both linear and cyclic electron flow. The data presented support the previous findings of Miller et al. (1991) that the accumulation of Ci by the CO2 concentrating mechanism is able to stimulate oxygen photoreduction, particularly so when CO2 fixation is inhibited by PCR cycle inhibitors such as glycolaldehyde. This effect is found with both high and low-Ci grown cells, but the potential for oxygen photoreduction is about two-fold higher in low-Ci grown cells. This greater potential for O2 photoreduction is also correlated with a higher ability of low-Ci cells to photoreduce H2O2. Experiments with a mutant which transports Ci but does not accumulate it internally, indicates that the stimulation of O2 photoreduction appears to be a direct effect of the internal accumulation of Ci rather than from its participation in the transport process. In the absence of Ci, no specific partial reactions of photosynthetic electron transport appear to be inhibited, and the PS 1 acceptors PNDA and MV as well as the PS 2 acceptor DMQ can all run electron transport at levels approaching those during active CO2 fixation. Measurements of P700(+) show that when the cells are depleted of Ci during photosynthesis, P700 becomes more oxidised. This indicates that the resupply of electrons from the intersystem chain is relatively more restricted under conditions of Ci limitation than is the availability of PS 1 electron acceptors. It is proposed that the accumulated Ci pool can directly stimulate the ability of O2 to act as a PS 1 acceptor and that the ability of PS 1 acceptors, such as O2, to relieve restrictions on intersystem electron transfer is perhaps a result of a reduction in cyclic electron flow and a subsequent increase in the oxidation state of the plastoquinone pool.
本文研究了无机碳在聚球藻 PCC7942 中的运输和积累对荧光猝灭、光合氧气还原以及线性和环式电子流的影响。所提供的数据支持了 Miller 等人（1991 年）的先前发现，即 CO2 浓缩机制积累 Ci 能够刺激氧气光还原，特别是在 CO2 固定被如甘油醛等 PCR 循环抑制剂抑制时。这种效应在高 Ci 和低 Ci 生长的细胞中都能观察到，但低 Ci 生长的细胞的氧气光还原潜力大约高两倍。这种更高的氧气光还原潜力也与低 Ci 细胞更能光还原 H2O2 的能力相关。用一种只能运输 Ci 而不能在内部积累 Ci 的突变体进行的实验表明，氧气光还原的刺激似乎是 Ci 内部积累的直接效应，而不是来自其参与运输过程。在没有 Ci 的情况下，光合作用电子传递的特定部分反应似乎没有被抑制，PS1 受体 PNDA 和 MV 以及 PS2 受体 DMQ 都可以在接近活跃 CO2 固定时的水平上进行电子传递。对 P700(+)的测量表明，当细胞在光合作用过程中耗尽 Ci 时，P700 变得更加氧化。这表明，在 Ci 限制条件下，从系统间链供应电子的相对更受限制，而 PS1 电子受体的可用性不受限制。本文提出，积累的 Ci 池可以直接刺激 O2 作为 PS1 受体的能力，而 O2 等 PS1 受体能够缓解系统间电子转移的限制，可能是由于环式电子流减少和质体醌池氧化状态增加的结果。
