Photosynthetic organisms use different means to regulate their photosynthetic activity in respond to different light conditions under which they grow. In this study, we analyzed changes in the photosystem I (PSI) light-harvesting complex I (LHCI) supercomplex from a red alga Cyanidioschyzon merolae, upon growing under three different light intensities, low light (LL), medium light (ML), and high light (HL). The results showed that the red algal PSI-LHCI is separated into two bands on blue-native PAGE, which are designated PSI-LHCI-A and PSI-LHCI-B, respectively, from cells grown under LL and ML. The former has a higher molecular weight and binds more Lhcr subunits than the latter. They are considered to correspond to the two types of PSI-LHCI identified by cryo-electron microscopic analysis recently, namely, the former with five Lhcrs and the latter with three Lhcrs. The amount of PSI-LHCI-A is higher in the LL-grown cells than that in the ML-grown cells. In the HL-grown cells, PSI-LHCI-A completely disappeared and only PSI-LHCI-B was observed. Furthermore, PSI core complexes without Lhcr attached also appeared in the HL cells. Fluorescence decay kinetics measurement showed that Lhcrs are functionally connected with the PSI core in both PSI-LHCI-A and PSI-LHCI-B obtained from LL and ML cells; however, Lhcrs in the PSI-LHCI-B fraction from the HL cells are not coupled with the PSI core. These results indicate that the red algal PSI not only regulates its antenna size but also adjusts the functional connection of Lhcrs with the PSI core in response to different light intensities.

光合生物使用不同的方式来调节它们的光合活性，以响应它们生长的不同光照条件。在这项研究中，我们分析了来自红藻Cyanidioschyzon merolae的光系统 I (PSI) 光捕获复合物 I (LHCI) 超复合物的变化, 在三种不同的光强度下生长，低光 (LL)、中光 (ML) 和高光 (HL)。结果表明，红藻 PSI-LHCI 在蓝天然 PAGE 上分离成两个条带，分别命名为 PSI-LHCI-A 和 PSI-LHCI-B，来自在 LL 和 ML 下生长的细胞。前者具有更高的分子量并且比后者结合更多的 Lhcr 亚基。它们被认为对应于最近通过低温电子显微镜分析确定的两种 PSI-LHCI，即前者具有 5 个 Lhcr，后者具有 3 个 Lhcr。LL 生长细胞中 PSI-LHCI-A 的量高于 ML 生长细胞中的 PSI-LHCI-A 量。在 HL 生长的细胞中，PSI-LHCI-A 完全消失，仅观察到 PSI-LHCI-B。此外，没有连接Lhcr的PSI核心复合物也出现在HL细胞中。荧光衰减动力学测量表明，Lhcrs 与从 LL 和 ML 细胞获得的 PSI-LHCI-A 和 PSI-LHCI-B 中的 PSI 核心功能连接；然而，来自 HL 细胞的 PSI-LHCI-B 部分中的 Lhcrs 不与 PSI 核心耦合。这些结果表明，红藻 PSI 不仅调节其天线尺寸，而且还响应不同的光强度调节 Lhcrs 与 PSI 核心的功能连接。