Laboratory of Biophysics and MicroSpectroscopy Centre, Wageningen University, 6703 HA, Wageningen, The Netherlands.
Proc Natl Acad Sci U S A. 2014 Mar 4;111(9):3460-5. doi: 10.1073/pnas.1319164111. Epub 2014 Feb 18.
Plants and green algae optimize photosynthesis in changing light conditions by balancing the amount of light absorbed by photosystems I and II. These photosystems work in series to extract electrons from water and reduce NADP(+) to NADPH. Light-harvesting complexes (LHCs) are held responsible for maintaining the balance by moving from one photosystem to the other in a process called state transitions. In the green alga Chlamydomonas reinhardtii, a photosynthetic model organism, state transitions are thought to involve 80% of the LHCs. Here, we demonstrate with picosecond-fluorescence spectroscopy on C. reinhardtii cells that, although LHCs indeed detach from photosystem II in state 2 conditions, only a fraction attaches to photosystem I. The detached antenna complexes become protected against photodamage via shortening of the excited-state lifetime. It is discussed how the transition from state 1 to state 2 can protect C. reinhardtii in high-light conditions and how this differs from the situation in plants.
植物和绿藻通过平衡光系统 I 和 II 吸收的光量来优化对不断变化的光照条件下的光合作用。这些光系统串联工作，从水中提取电子，并将 NADP(+)还原为 NADPH。光捕获复合物（LHCs）通过在一个称为状态转变的过程中从一个光系统转移到另一个光系统，负责维持平衡。在绿藻莱茵衣藻中，一种光合作用的模式生物，人们认为状态转变涉及 80%的 LHCs。在这里，我们通过皮秒荧光光谱法在 C. reinhardtii 细胞上证明，尽管 LHCs 在状态 2 条件下确实从光系统 II 上脱离，但只有一部分附着在光系统 I 上。通过缩短激发态寿命，脱离的天线复合物受到保护，免受光损伤。本文讨论了从状态 1 到状态 2 的转变如何在高光条件下保护 C. reinhardtii，以及这与植物的情况有何不同。
