不同光环境集胞藻循环电子传递与类梅勒反应

Interplay of Cyclic Electron Transport and Mehler-like Reaction in Synechocystis Under Different Light Regimes

光是光合作用不可或缺的底物。然而过量的光照会对光合生物造成氧化胁迫和严重的损害。为了应对持续变化的光环境,蓝藻演化形成了灵活的电子传递网络。围绕光系统I(photosystem I,PSI)的循环电子传递(cyclic electron transport,CET)将电子从铁氧还蛋白Fd回流到质体醌(plastoquinone,PQ)库,产生ATP且不积累NADPH。在蓝藻和高等植物中发现了2种不同的CET途径,即NDH依赖途径和PGR5依赖途径。蓝藻中黄素二铁蛋白Flv1/Flv3参与了类梅勒(Mehler-like)反应,从PSI接受电子直接将氧气还原为水,且没有活性氧的形成。以集胞藻为试验材料,通过分析不同的CET和Flv突变株在不同光照条件下的生理特征以及其P700氧化/还原动力学,进而研究CET途径和类梅勒反应在集胞藻中的功能。结果表明NDH-1复合体对CET的贡献率超过90%,维持细胞能在持续高光环境下生长,而迅速应激的类梅勒反应在缓解瞬时高光胁迫时发挥了重要作用。因此我们认为在集胞藻中NDH-1介导的循环电子途径是稳固支持其适应高光逆境的主要机制,而类梅勒反应则是在现有主要途径严重不足时的1个备用途径。响应迅速的FLV路径是野生型和NDH-1突变株的补足。

Light is an essential substrate for photosynthesis.However,excessive light could cause oxidative stress and severe damages of photosynthetic organisms.To cope with constantly changing light environments,cyanobacteria have developed flexible electron transport network.Cyclic electron transport(CET)around photosystem I(PSI)recycles electrons from ferredoxin to plastoquinone pool and generates ATP without NADPH accumulation.Two distinct CET pathways consisting of NDH-dependent route and PGR5-dependent route have been identified both in cyanobacteria and plants.Cyanobacterial flavodiiron proteins Flv1 and Flv3 functioning in Mehler-like reaction accept electrons after PSI to reduce oxygen to water without formation of reactive oxygen species.Here,we studied the function of CET routes and Mehler-like reaction in Synechocystis by physiological characterization under different light regimes and kinetic analysis of P700 oxidation/reduction using various CET and Flv mutants.It showed that NDH-1 complexes contributed over 90%of CET and sustained cell growth under steady high light condition,while Mehlerlike reaction activated rapidly was responsible for releasing transient high light pressure.We proposed that NDH-1 dependent CET was the major mechanism in Synechocystis robustly supporting high light acclimation,whereas Mehler-like reaction was the spare route operating when the existing main path was largely insufficient.The fast responded FLV route could be a complementation of CET in the WT as well as NDH-1 defected mutant M55.