Kono Masaru, Yamori Wataru, Suzuki Yoshihiro, Terashima Ichiro
Department of Biological Sciences, School of Science, The University of Tokyo, Hongo, Bunkyo-ku, Tokyo, Japan.
Plant Cell Physiol. 2017 Jan 1;58(1):35-45. doi: 10.1093/pcp/pcw215.
It has been reported that PSI photoinhibition is induced even in wild-type plants of Arabidopsis thaliana, rice and other species by exposure of leaves to fluctuating light (FL) for a few hours. Because plants are exposed to FL in nature, they must possess protective mechanisms against the FL-induced photodamage. Here, using A. thaliana grown at various irradiances, we examined PSI photoprotection by far-red (FR) light at intensities comparable with those observed in nature. Dark-treated leaves were illuminated by red FL alternating high/low light at 1,200/30 µmol m-2 s-1 for 800 ms/10 s. By this FL treatment without FR light for 120 min, the level of photo-oxidizable P700 was decreased by 30% even in the plants grown at high irradiances. The addition of continuous FR light during the FL suppressed this damage almost completely. With FR light, P700 was kept in a more oxidized state in both low- and high-light phases. The protective effect of FR light was diminished more in mutants of the NADH dehydrogenase-like complex (NDH)-mediated cyclic electron flow around PSI (CEF-PSI) than in the PGR5 (proton gradient regulation 5)-mediated CEF-PSI, indicating that the NDH-mediated CEF-PSI would be a major contributor to PSI photoprotection in the presence of FR light. We also confirmed that PSI photoinhibition decreased with the increase in growth irradiance in A. thaliana and field-grown plants, and that this PSI photodamage was largely suppressed by addition of FR light. These results clearly indicate that the most effective PSI protection is realized in the presence of FR light.
据报道，即使是拟南芥、水稻和其他物种的野生型植株，其叶片暴露于波动光（FL）数小时也会诱导PSI光抑制。由于植物在自然环境中会受到FL照射，它们必定具备针对FL诱导的光损伤的保护机制。在此，我们使用在不同辐照度下生长的拟南芥，研究了强度与自然环境中相当的远红光（FR）对PSI的光保护作用。对暗处理的叶片交替进行1200/30 μmol m-2 s-1的高/低红光FL照射，每次800毫秒/10秒。通过这种无FR光的FL处理120分钟，即使是在高辐照度下生长的植株，其可光氧化的P700水平也降低了30%。在FL处理期间添加连续的FR光几乎完全抑制了这种损伤。有FR光时，P700在低光和高光阶段都保持在更氧化的状态。与PGR5（质子梯度调节5）介导的围绕PSI的循环电子流（CEF-PSI）相比，NADH脱氢酶样复合体（NDH）介导的CEF-PSI突变体中FR光的保护作用减弱得更多，这表明在有FR光存在时，NDH介导的CEF-PSI对PSI光保护起主要作用。我们还证实，拟南芥和田间种植的植株中，PSI光抑制随生长辐照度的增加而降低，并且添加FR光可在很大程度上抑制这种PSI光损伤。这些结果清楚地表明，在有FR光存在时可实现最有效的PSI保护。
