Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, China; University of Chinese Academy of Sciences, Beijing 100049, China.
Key Laboratory of Economic Plants and Biotechnology, Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, Yunnan 650201, China.
Biochim Biophys Acta Bioenerg. 2020 Sep 1;1861(9):148235. doi: 10.1016/j.bbabio.2020.148235. Epub 2020 May 30.
Photosynthetic electron flux from water via photosystem II (PSII) and PSI to oxygen (water-water cycle) may act as an alternative electron sink under fluctuating light in angiosperms. We measured the P700 redox kinetics and electrochromic shift signal under fluctuating light in 11 Camellia species and tobacco leaves. Upon dark-to-light transition, these Camellia species showed rapid re-oxidation of P700. However, this rapid re-oxidation of P700 was not observed when measured under anaerobic conditions, as was in experiment with tobacco performed under aerobic conditions. Therefore, photo-reduction of O mediated by water-water cycle was functional in these Camellia species but not in tobacco. Within the first 10 s after transition from low to high light, PSI was highly oxidized in these Camellia species but was over-reduced in tobacco leaves. Furthermore, such rapid oxidation of PSI in these Camellia species was independent of the formation of trans-thylakoid proton gradient (ΔpH). These results indicated that in addition to ΔpH-dependent photosynthetic control, the water-water cycle can protect PSI against photoinhibition under fluctuating light in these Camellia species. We here propose that the water-water cycle is an overlooked strategy for photosynthetic regulation under fluctuating light in angiosperms.
在波动光下，来自水的通过光系统 II (PSII) 和 PSI 到氧气的光合电子流（水-水循环）可能作为被子植物中波动光下的替代电子汇。我们测量了 11 种茶花和烟草叶片在波动光下的 P700 氧化还原动力学和电致变色位移信号。在暗至光的转变过程中，这些茶花迅速重新氧化 P700。然而，当在厌氧条件下进行测量时，如在有氧条件下用烟草进行的实验中，并没有观察到这种 P700 的快速氧化。因此，水-水循环介导的 O 的光还原在这些茶花中是功能性的，但在烟草中则不是。在从低光到高光的转变后的前 10 秒内，PSI 在这些茶花中高度氧化，但在烟草叶片中过度还原。此外，PSI 在这些茶花中的这种快速氧化不依赖于跨类囊体质子梯度（ΔpH）的形成。这些结果表明，除了依赖于 ΔpH 的光合作用控制之外，水-水循环可以在这些茶花中保护 PSI 免受波动光下的光抑制。我们在这里提出，水-水循环是被子植物在波动光下光合作用调节中被忽视的策略。
