Ogawa Takako, Takahashi Hiroko, Nishiyama Yoshitaka, Hihara Yukako, Sonoike Kintake
Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama, 338-8570, Japan.
Faculty of Education and Integrated Arts and Sciences, Waseda University, 2-2 Wakamatsu-cho, Shinjuku-ku, Tokyo, 162-8480, Japan.
Photosynth Res. 2025 Jul 9;163(4):38. doi: 10.1007/s11120-025-01159-0.
Under high-light conditions, the dissipation of excess energy as heat in the light-harvesting antenna is essential for photosynthetic organisms to protect the photosynthetic machinery. In the case of cyanobacteria, however, the induction of the thermal dissipation in the antennae is insufficient to dissipate all excess energy, which is manifested as the increase in the steady-state level of chlorophyll fluorescence (Fs) under high light. To elucidate the underlying cause of the incomplete dissipation of excess light in the antenna, we investigated the impact of depletion and overexpression of orange carotenoid protein (OCP), which is essential to induce thermal dissipation in the antenna, on photosynthesis in Synechocystis sp. PCC 6803. The suppression of the OCP-dependent thermal dissipation resulted in elevated Fs with a constant yield of photosynthesis, suggesting that the light-induced increase in Fs might function as an acclimation mechanism to high light, which compensated for the lower OCP-dependent thermal dissipation. By contrast, over-induction of the OCP-dependent thermal dissipation decreased not only Fs but also the yield of photosynthesis under high light, due to the reduced energy transfer from the antenna to photosystem II. These results indicate that the complete removal of excess energy via the OCP-dependent mechanism has a drawback in photosynthetic efficiency under high-light conditions, and the strategy independent of OCP is employed to cope with excess light without lowering the yield of photosynthesis in cyanobacteria.
在高光条件下，光合生物将捕光天线中多余的能量以热的形式耗散对于保护光合机构至关重要。然而，对于蓝细菌而言，天线中热耗散的诱导不足以耗散所有多余的能量，这表现为高光下叶绿素荧光稳态水平（Fs）的增加。为了阐明天线中多余光不能完全耗散的潜在原因，我们研究了橙色类胡萝卜素蛋白（OCP）的缺失和过表达对集胞藻PCC 6803光合作用的影响，OCP对于诱导天线中的热耗散至关重要。抑制依赖OCP的热耗散导致Fs升高，光合作用产量保持恒定，这表明光诱导的Fs增加可能作为一种对高光的适应机制，补偿了较低的依赖OCP的热耗散。相比之下，过度诱导依赖OCP的热耗散不仅降低了Fs，还降低了高光下的光合作用产量，这是由于从天线到光系统II的能量转移减少。这些结果表明，通过依赖OCP的机制完全去除多余能量在高光条件下对光合效率有不利影响，并且蓝细菌采用独立于OCP的策略来应对多余的光，而不降低光合作用产量。
