烟草叶片中呼吸电子传递途径在缓解叶绿体PSⅡ光抑制中的作用

前期研究发现线粒体交替氧化酶(AOX)呼吸途径对叶绿体光系统II(PSII)的光抑制有明显的缓解作用。线粒体内另一条呼吸途径——细胞色素氧化酶(COX)呼吸途径是否也具有光保护作用尚不清楚。该文通过荧光快速诱导动力学和荧光淬灭分析,解析了烟草(Nicotiana tabacum)叶片中COX途径对PSII光保护的贡献及其与AOX途径的关系。结果表明,强光处理后PSII活性在所有叶片中均下降。AOX途径受抑明显加速了叶片PSII活性的下降。而当COX途径受抑后,叶片PSII活性的下降与水处理的对照叶片无明显差异。当AOX途径与COX途径同时受抑时,叶片PSII活性的下降比单独抑制AOX途径时更严重。此外,呼吸电子传递受抑均导致叶片非光化学淬灭(NPQ)增加,AOX途径受抑导致的NPQ上调比COX途径受抑时更明显,AOX和COX途径同时受抑时NPQ的增幅最大。上述结果表明,烟草叶片中COX途径和AOX途径均参与PSⅡ的光保护。当COX途径受抑时,其光保护功能可以被AOX途径和NPQ补偿,而AOX途径的光保护作用不能被COX途径和NPQ完全补偿。

Effects of the Respiratory Electron Transport Pathways in Relieving Photoinhibition of Chloroplast PSII in Tobacco Leaves

Previous studies have shown that the mitochondrial alternative oxidase (AOX) respiratory pathway contributes to the photoprotection of photosystem II (PSII) under high light. However, the role of another respiratory pathway in mitochondria, the cytochrome-respiratory (COX) pathway, to photoprotection under high light remains unknown. Here, we studied the contributions of COX and AOX pathways to PSII photoprotection, as well as the relationship between COX and AOX pathways in PSII photoprotection in tobacco leaves under high light using chlorophyll fluorescence transients and chlorophyll fluorescence quenching approaches. After high light treatment, the PSII activity decreased in all leaves. The inhibition of AOX pathway significantly accelerated the decrease of PSII activity in leaves. However, there was no significant difference between the PSII activity in the leaves pretreated with COX pathway inhibitor and water-pretreated control leaves. When both AOX and COX pathways are inhibited in leaves, the decrease in PSII activity was severe, than that of leaves pretreated by only AOX pathway inhibitor. In addition, inhibition of respiratory electron transport resulted in an increase of non-photochemical quenching (NPQ). The up-regulation of NPQ caused by AOX pathway inhibitor was more obviously than that caused by COX pathway inhibitor, and the increase of NPQ was highest when both AOX and COX pathways were inhibited. These results indicate that both COX and AOX pathways contribute to the PSII photoprotection in tobacco leaves under high light. In addition, when COX pathway is inhibited, its photoprotective function can be compensated by AOX pathway and NPQ, however, photoprotection of AOX pathway cannot be completely compensated by COX pathway and NPQ.