LaserLaB, Department of Physics and Astronomy, Faculty of Science, Vrije Universiteit Amsterdam, De Boelelaan 1081, 1081 HV, Amsterdam, The Netherlands.
Swammerdam Institute for Life Sciences, University of Amsterdam, 1098 XH, Amsterdam, The Netherlands.
Photosynth Res. 2018 Aug;137(2):307-320. doi: 10.1007/s11120-018-0505-0. Epub 2018 Mar 29.
Photosynthetic activity and respiration share the thylakoid membrane in cyanobacteria. We present a series of spectrally resolved fluorescence experiments where whole cells of the cyanobacterium Synechocystis sp. PCC 6803 and mutants thereof underwent a dark-to-light transition after different dark-adaptation (DA) periods. Two mutants were used: (i) a PSI-lacking mutant (ΔPSI) and (ii) M55, a mutant without NAD(P)H dehydrogenase type-1 (NDH-1). For comparison, measurements of the wild-type were also carried out. We recorded spectrally resolved fluorescence traces over several minutes with 100 ms time resolution. The excitation light was at 590 nm so as to specifically excite the phycobilisomes. In ΔPSI, DA time has no influence, and in dichlorophenyl-dimethylurea (DCMU)-treated samples we identify three main fluorescent components: PB-PSII complexes with closed (saturated) RCs, a quenched or open PB-PSII complex, and a PB-PSII 'not fully closed.' For the PSI-containing organisms without DCMU, we conclude that mainly three species contribute to the signal: a PB-PSII-PSI megacomplex with closed PSII RCs and (i) slow PB → PSI energy transfer, or (ii) fast PB → PSI energy transfer and (iii) complexes with open (photochemically quenched) PSII RCs. Furthermore, their time profiles reveal an adaptive response that we identify as a state transition. Our results suggest that deceleration of the PB → PSI energy transfer rate is the molecular mechanism underlying a state 2 to state 1 transition.
在蓝细菌中，光合作用和呼吸作用共享类囊体膜。我们提出了一系列光谱分辨荧光实验，其中蓝藻聚球藻 PCC 6803 的整个细胞及其突变体在不同暗适应（DA）期后经历暗至光的转变。使用了两种突变体：（i）PSI 缺失突变体（ΔPSI）和（ii）M55，这是一种没有 NAD(P)H 脱氢酶类型-1（NDH-1）的突变体。为了比较，还对野生型进行了测量。我们用 100 ms 的时间分辨率记录了几分钟的光谱分辨荧光轨迹。激发光在 590nm 处，以便特异性地激发藻胆体。在 ΔPSI 中，DA 时间没有影响，而在二氯苯基-二甲基脲（DCMU）处理的样品中，我们鉴定了三个主要的荧光成分：具有闭合（饱和）RC 的 PB-PSII 复合物、猝灭或打开的 PB-PSII 复合物以及 PB-PSII“未完全闭合”。对于不含 DCMU 的含有 PSI 的生物体，我们得出结论，主要有三种物质对信号有贡献：具有闭合 PSII RC 的 PB-PSII-PSI 巨复合物和（i）缓慢的 PB→PSI 能量转移，或（ii）快速的 PB→PSI 能量转移和（iii）具有打开（光化学猝灭）PSII RC 的复合物。此外，它们的时间曲线揭示了一种适应性反应，我们将其识别为状态转变。我们的结果表明，PB→PSI 能量转移率的减速是状态 2 到状态 1 转变的分子机制。
