School of Biological and Chemical Sciences, Queen Mary University of London, London, United Kingdom.
Biophys J. 2012 Jun 20;102(12):2761-71. doi: 10.1016/j.bpj.2012.05.004. Epub 2012 Jun 19.
The maximum chlorophyll fluorescence lifetime in isolated photosystem II (PSII) light-harvesting complex (LHCII) antenna is 4 ns; however, it is quenched to 2 ns in intact thylakoid membranes when PSII reaction centers (RCIIs) are closed (Fm). It has been proposed that the closed state of RCIIs is responsible for the quenching. We investigated this proposal using a new, to our knowledge, model system in which the concentration of RCIIs was highly reduced within the thylakoid membrane. The system was developed in Arabidopsis thaliana plants under long-term treatment with lincomycin, a chloroplast protein synthesis inhibitor. The treatment led to 1), a decreased concentration of RCIIs to 10% of the control level and, interestingly, an increased antenna component; 2), an average reduction in the yield of photochemistry to 0.2; and 3), an increased nonphotochemical chlorophyll fluorescence quenching (NPQ). Despite these changes, the average fluorescence lifetimes measured in Fm and Fm' (with NPQ) states were nearly identical to those obtained from the control. A 77 K fluorescence spectrum analysis of treated PSII membranes showed the typical features of preaggregation of LHCII, indicating that the state of LHCII antenna in the dark-adapted photosynthetic membrane is sufficient to determine the 2 ns Fm lifetime. Therefore, we conclude that the closed RCs do not cause quenching of excitation in the PSII antenna, and play no role in the formation of NPQ.
分离的光系统 II（PSII）光捕获复合物（LHCII）天线中的叶绿素荧光寿命最大值为 4 ns；然而，当 PSII 反应中心（RCII）关闭（Fm）时，它在完整的类囊体膜中被猝灭至 2 ns。有人提出 RCII 的关闭状态是猝灭的原因。我们使用一种新的、据我们所知的模型系统来研究这个假设，在该系统中，RCII 的浓度在类囊体膜内被高度降低。该系统是在拟南芥植物中通过长期使用林可霉素（一种叶绿体蛋白合成抑制剂）处理而开发的。该处理导致：1）RCII 的浓度降低到对照水平的 10%，有趣的是，天线组件增加；2）光化学产量平均降低到 0.2；3）非光化学叶绿素荧光猝灭（NPQ）增加。尽管发生了这些变化，但在 Fm 和 Fm'（带 NPQ）状态下测量的平均荧光寿命与从对照中获得的几乎相同。用处理过的 PSII 膜进行的 77 K 荧光光谱分析显示出 LHCII 预聚集的典型特征，表明暗适应光合膜中 LHCII 天线的状态足以确定 2 ns 的 Fm 寿命。因此，我们得出结论，关闭的 RC 不会导致 PSII 天线中激发的猝灭，也不会在 NPQ 的形成中发挥作用。
