School of Biological and Chemical Sciences, Queen Mary University of London, Mile End, Bancroft Road, Fogg Building, London E14NS, UK.
Planta. 2011 Jun;233(6):1253-64. doi: 10.1007/s00425-011-1380-5. Epub 2011 Feb 22.
The efficiency of photosystem II antenna complexes (LHCs) in higher plants must be regulated to avoid potentially damaging overexcitation of the reaction centre in excess light. Regulation is achieved via a feedback mechanism known as non-photochemical quenching (NPQ), triggered the proton gradient (ΔpH) causing heat dissipation within the LHC antenna. ΔpH causes protonation of the LHCs, the PsbS protein and triggers the enzymatic de-epoxidation of the xanthophyll, violaxanthin, to zeaxanthin. A key step in understanding the mechanism is to decipher whether PsbS and zeaxanthin cooperate to promote NPQ. To obtain clues about their respective functions we studied the effects of PsbS and zeaxanthin on the rates of NPQ formation and relaxation in wild-type Arabidopsis leaves and those overexpressing PsbS (L17) or lacking zeaxanthin (npq1). Overexpression of PsbS was found to increase the rate of NPQ formation, as previously reported for zeaxanthin. However, PsbS overexpression also increased the rate of NPQ relaxation, unlike zeaxanthin, which is known decrease the rate. The enhancement of PsbS levels in plants lacking zeaxanthin (npq1) by either acclimation to high light or crossing with L17 plants showed that the effect of PsbS was independent of zeaxanthin. PsbS levels also affected the kinetics of the 535 nm absorption change (ΔA535), which monitors the formation of the conformational state of the LHC antenna associated with NPQ, in an identical way. The antagonistic action of PsbS and zeaxanthin with respect to NPQ and ΔA535 relaxation kinetics suggests that the two molecules have distinct regulatory functions.
高等植物光系统 II 天线复合物 (LHCs) 的效率必须受到调节，以避免在过量光下反应中心潜在的过度激发。这种调节是通过一种称为非光化学猝灭 (NPQ) 的反馈机制实现的，该机制触发质子梯度 (ΔpH)，导致 LHC 天线内的热量耗散。ΔpH 导致 LHCs、PsbS 蛋白质子化，并触发叶黄素、 violaxanthin 的酶促去环氧化作用，生成 zeaxanthin。理解该机制的一个关键步骤是确定 PsbS 和 zeaxanthin 是否合作促进 NPQ。为了获得关于它们各自功能的线索，我们研究了 PsbS 和 zeaxanthin 对野生型拟南芥叶片和过表达 PsbS (L17) 或缺乏 zeaxanthin (npq1) 的叶片 NPQ 形成和弛豫速率的影响。正如先前报道的 zeaxanthin 一样，发现过表达 PsbS 会增加 NPQ 的形成速率。然而，与已知降低速率的 zeaxanthin 不同，PsbS 过表达也增加了 NPQ 的弛豫速率。通过高光照适应或与 L17 植物杂交，在缺乏 zeaxanthin (npq1) 的植物中增加 PsbS 水平的实验表明，PsbS 的作用独立于 zeaxanthin。PsbS 水平也以相同的方式影响 535nm 吸收变化 (ΔA535) 的动力学，该变化监测与 NPQ 相关的 LHC 天线构象状态的形成。PsbS 和 zeaxanthin 对 NPQ 和 ΔA535 弛豫动力学的拮抗作用表明，这两个分子具有不同的调节功能。
