Department of Biological and Environmental Science, Faculty of Agriculture, Graduate School of Agricultural Science, Kobe University, 1-1 Rokkodai-cho, Nada-ku, Kobe, 657-8501, Japan.
Core Research for Environmental Science and Technology, Japan Science and Technology Agency, 7 Goban-cho, Chiyoda-ku, Tokyo, 102-0076, Japan.
Photosynth Res. 2018 Aug;137(2):241-250. doi: 10.1007/s11120-018-0495-y. Epub 2018 Mar 8.
Oxygenic phototrophs are vulnerable to damage by reactive oxygen species (ROS) that are produced in photosystem I (PSI) by excess photon energy over the demand of photosynthetic CO assimilation. In plant leaves, repetitive short-pulse (rSP) illumination produces ROS to inactivate PSI. The production of ROS is alleviated by oxidation of the reaction center chlorophyll in PSI, P700, during the illumination with the short-pulse light, which is supported by flavodiiron protein (FLV). In this study, we found that in the cyanobacterium Synechocystis sp. PCC 6803 P700 was oxidized and PSI was not inactivated during rSP illumination even in the absence of FLV. Conversely, the mutant deficient in respiratory terminal oxidases was impaired in P700 oxidation during the illumination with the short-pulse light to suffer from photo-oxidative damage in PSI. Interestingly, the other cyanobacterium Synechococcus sp. PCC 7002 could not oxidize P700 without FLV during rSP illumination. These data indicate that respiratory terminal oxidases are critical to protect PSI from ROS damage during rSP illumination in Synechocystis sp. PCC 6803 but not Synechococcus sp. PCC 7002.
好氧光合生物容易受到活性氧（ROS）的伤害，ROS 是由光合作用 CO 同化需求过剩的光子能量在光系统 I（PSI）中产生的。在植物叶片中，重复短脉冲（rSP）光照会产生 ROS 来使 PSI 失活。在短脉冲光照射下，PSI 中的反应中心叶绿素被氧化，从而缓解了 ROS 的产生，这一过程得到了黄素铁蛋白（FLV）的支持。在这项研究中，我们发现，在蓝藻集胞藻 PCC 6803 中，即使没有 FLV，rSP 光照也会导致 P700 氧化，而 PSI 不会失活。相反，呼吸末端氧化酶缺陷的突变体在短脉冲光照射下的 P700 氧化受到损害，从而导致 PSI 发生光氧化损伤。有趣的是，另一种蓝藻聚球藻 PCC 7002 在没有 FLV 的情况下，无法在 rSP 光照下氧化 P700。这些数据表明，在集胞藻 PCC 6803 中，呼吸末端氧化酶对于保护 PSI 免受 rSP 光照下的 ROS 损伤至关重要，但在聚球藻 PCC 7002 中则不是这样。
