Research Institute for Interdisciplinary Science and Graduate School of Natural Science and Technology, Okayama University, 3-1-1 Tsushima Naka, Okayama 700-8530, Japan.
Graduate School of Science, Kobe University, Kobe 657-8501, Japan.
Biochim Biophys Acta Bioenerg. 2018 Jul;1859(7):524-530. doi: 10.1016/j.bbabio.2018.04.003. Epub 2018 Apr 13.
Maintenance of energy balance under changeable light conditions is an essential function of photosynthetic organisms to achieve efficient photochemical reactions. Among the photosynthetic organisms, diatoms possess light-harvesting fucoxanthin chlorophyll (Chl) a/c-binding protein (FCP) as peripheral antennas. However, how diatoms regulate excitation-energy distribution between FCP and the two photosystem cores during light adaptation is poorly understood. In this study, we examined spectroscopic properties of a marine diatom Chaetoceros gracilis adapted in the dark and at photosynthetic photon flux density at 30 and 300 μmol photons m s. Absorption spectra at 77 K showed significant changes in the Soret region, and 77-K steady-state fluorescence spectra showed significant differences in the spectral shape and relative fluorescence intensity originating from both PSII and PSI, among the cells grown under different light conditions. These results suggest alterations of pigment composition and their interactions under the different light conditions. These alterations affected the excitation-energy dynamics monitored by picosecond time-resolved fluorescence analyses at 77 K significantly. The contributions of Chls having lower energy levels than the reaction center Chls in the two photosystems to the energy dynamics were clearly identified in the three cells but with presumably different roles. These findings provide insights into the regulatory mechanism of excitation-energy balance in diatoms under various light conditions.
在多变的光照条件下维持能量平衡是光合生物实现高效光化学反应的基本功能。在光合生物中，硅藻具有光捕获的叶黄素叶绿素 a/c 结合蛋白（FCP）作为外周天线。然而，硅藻如何在光适应过程中调节 FCP 和两个光系统核心之间的激发能分布尚不清楚。在这项研究中，我们研究了在黑暗中和在 30 和 300 µmol 光子 m s 的光合光子通量密度下适应的海洋硅藻 Chaetoceros gracilis 的光谱性质。77 K 时的吸收光谱在 Soret 区域显示出显著变化，77 K 稳态荧光光谱显示出源自 PSII 和 PSI 的光谱形状和相对荧光强度的显著差异，这些差异是在不同光照条件下生长的细胞之间产生的。这些结果表明在不同光照条件下，色素组成及其相互作用发生了改变。这些变化显著影响了在 77 K 下通过皮秒时间分辨荧光分析监测的激发能动力学。在三个细胞中清楚地识别了两个光系统中比反应中心叶绿素具有更低能级的叶绿素对能量动力学的贡献，但可能具有不同的作用。这些发现为在各种光照条件下硅藻中激发能平衡的调节机制提供了深入的了解。
