Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan.
CREST, JST, Sapporo, Japan.
Plant Cell Physiol. 2019 May 1;60(5):1098-1108. doi: 10.1093/pcp/pcz026.
Energy dissipation is crucial for land and shallow-water plants exposed to direct sunlight. Almost all green plants dissipate excess excitation energy to protect the photosystem reaction centers, photosystem II (PSII) and photosystem I (PSI), and continue to grow under strong light. In our previous work, we reported that about half of the photosystem reaction centers form a PSI-PSII megacomplex in Arabidopsis thaliana, and that the excess energy was transferred from PSII to PSI fast. However, the physiological function and structure of the megacomplex remained unclear. Here, we suggest that high-light adaptable sun-plants accumulate the PSI-PSII megacomplex more than shade-plants. In addition, PSI of sun-plants has a deep trap to receive excitation energy, which is low-energy chlorophylls showing fluorescence maxima longer than 730 nm. This deep trap may increase the high-light tolerance of PSI by improving excitation energy dissipation. Electron micrographs suggest that one PSII dimer is directly sandwiched between two PSIs with 2-fold rotational symmetry in the basic form of the PSI-PSII megacomplex in green plants. This structure should enable fast energy transfer from PSII to PSI and allow energy in PSII to be dissipated via the deep trap in PSI.
能量耗散对于暴露在直射阳光下的陆生和浅水植物至关重要。几乎所有的绿色植物都会耗散多余的激发能，以保护光系统反应中心、光系统 II（PSII）和光系统 I（PSI），并在强光下继续生长。在我们之前的工作中，我们报告说，在拟南芥中，大约有一半的光系统反应中心形成了一个 PSI-PSII 超级复合物，多余的能量从 PSII 快速转移到 PSI。然而，该超级复合物的生理功能和结构仍不清楚。在这里，我们提出，高光适应性的阳性植物比阴生植物积累更多的 PSI-PSII 超级复合物。此外，阳性植物的 PSI 具有一个深陷阱来接收激发能，这是低能叶绿素，其荧光最大峰长于 730nm。这个深陷阱可能通过提高激发能耗散来提高 PSI 的高光耐受性。电子显微镜照片表明，在绿色植物的 PSI-PSII 超级复合物的基本形式中，一个 PSII 二聚体以 2 倍旋转对称的方式直接夹在两个 PSI 之间。这种结构应该能够使能量从 PSII 快速转移到 PSI，并允许 PSII 中的能量通过 PSI 中的深陷阱耗散。
