Chukhutsina Volha, Bersanini Luca, Aro Eva-Mari, van Amerongen Herbert
Laboratory of Biophysics, Wageningen University, P.O. Box 8128, 6700 ET, Wageningen, The Netherlands.
BioSolarCells, P.O. Box 98, 6700 AB Wageningen, The Netherlands.
Sci Rep. 2015 Sep 21;5:14193. doi: 10.1038/srep14193.
Photosynthetic organisms cope with changes in light quality by balancing the excitation energy flow between photosystems I (PSI) and II (PSII) through a process called state transitions. Energy redistribution has been suggested to be achieved by movement of the light-harvesting phycobilisome between PSI and PSII, or by nanometre scale rearrangements of the recently discovered PBS-PSII-PSI megacomplexes. The alternative 'spillover' model, on the other hand, states that energy redistribution is achieved by mutual association/dissociation of PSI and PSII. State transitions have always been studied by changing the redox state of the electron carriers using electron transfer inhibitors, or by applying illumination conditions with different colours. However, the molecular events during natural dark-to-light transitions in cyanobacteria have largely been overlooked and still remain elusive. Here we investigated changes in excitation energy transfer from phycobilisomes to the photosystems upon dark-light transitions, using picosecond fluorescence spectroscopy. It appears that megacomplexes are not involved in these changes, and neither does spillover play a role. Instead, the phycobilisomes partly energetically uncouple from PSI in the light but hardly couple to PSII.
光合生物通过一种称为状态转换的过程，平衡光系统I（PSI）和光系统II（PSII）之间的激发能流，来应对光质的变化。有人提出，能量重新分配是通过捕光藻胆体在PSI和PSII之间的移动，或者通过最近发现的PBS-PSII-PSI巨型复合体的纳米级重排来实现的。另一方面，另一种“溢出”模型认为，能量重新分配是通过PSI和PSII的相互结合/解离来实现的。状态转换一直是通过使用电子传递抑制剂改变电子载体的氧化还原状态，或者通过应用不同颜色的光照条件来进行研究的。然而，蓝细菌在自然的暗-光转换过程中的分子事件在很大程度上被忽视了，仍然难以捉摸。在这里，我们使用皮秒荧光光谱法研究了暗-光转换过程中从藻胆体到光系统的激发能转移变化。看来巨型复合体并不参与这些变化，溢出也不起作用。相反，藻胆体在光照下部分地与PSI在能量上解偶联，但几乎不与PSII偶联。
