School of Life Science and Technology, Tokyo Institute of Technology, Yokohama, 226-8501, Japan.
Division of Environmental Photobiology, National Institute for Basic Biology, Okazaki, 444-8585, Japan.
Photosynth Res. 2019 Mar;139(1-3):359-365. doi: 10.1007/s11120-018-0533-9. Epub 2018 Jun 18.
The proton motive force (PMF) across the chloroplast thylakoid membrane that is generated by electron transport during photosynthesis is the driving force for ATP synthesis in plants. The PMF mainly arises from the oxidation of water in photosystem II and from electron transfer within the cytochrome bf complex. There are two electron transfer pathways related to PMF formation: linear electron flow and cyclic electron flow. Proton gradient regulation 5 (PGR5) is a major component of the cyclic electron flow pathway, and the Arabidopsis pgr5 mutant shows a substantial reduction in the PMF. How the PGR5-dependent cyclic electron flow contributes to ATP synthesis has not, however, been fully delineated. In this study, we monitored in vivo ATP levels in Arabidopsis chloroplasts in real time using a genetically encoded bioluminescence-based ATP indicator, Nano-lantern(ATP1). The increase in ATP in the chloroplast stroma of pgr5 leaves upon illumination with actinic light was significantly slower than in wild type, and the decrease in ATP levels when this illumination stopped was significantly faster in pgr5 leaves than in wild type. These results indicated that PGR5-dependent cyclic electron flow around photosystem I helps to sustain the rate of ATP synthesis, which is important for growth under fluctuating light conditions.
在光合作用过程中，电子传递产生的跨叶绿体类囊体膜质子动力势（PMF）是植物中 ATP 合成的驱动力。PMF 主要源于光系统 II 中水的氧化和细胞色素 bf 复合物内的电子传递。有两种与 PMF 形成相关的电子传递途径：线性电子流和循环电子流。质子梯度调节因子 5（PGR5）是循环电子流途径的主要组成部分，拟南芥 pgr5 突变体中的 PMF 显著减少。然而，PGR5 依赖性循环电子流如何促进 ATP 合成尚未完全阐明。在这项研究中，我们使用基于遗传编码的生物发光 ATP 指示剂 Nano-lantern(ATP1)实时监测拟南芥叶绿体中的体内 ATP 水平。在强光下，pgr5 叶片的叶绿体基质中 ATP 的增加明显比野生型慢，而当这种光照停止时，pgr5 叶片中 ATP 水平的下降明显比野生型快。这些结果表明，PGR5 依赖性的围绕光系统 I 的循环电子流有助于维持 ATP 合成的速率，这对于在波动的光照条件下的生长很重要。
