Department of Horticulture, Zijingang Campus, Zhejiang University, Yuhangtang Road 866, Hangzhou 310058, PR China.
Biochem Biophys Res Commun. 2012 Sep 28;426(3):390-4. doi: 10.1016/j.bbrc.2012.08.100. Epub 2012 Aug 29.
Brassinosteroids (BRs) play important roles in plant growth, development, photosynthesis and stress tolerance; however, the mechanism underlying BR-enhanced photosynthesis is currently unclear. Here, we provide evidence that an increase in the BR level increased the quantum yield of PSII, activities of Rubisco activase (RCA) and fructose-1,6-bisphosphatase (FBPase), and CO(2) assimilation. BRs upregulated the transcript levels of genes and activity of enzymes involved in the ascorbate-glutathione cycle in the chloroplasts, leading to an increased ratio of reduced (GSH) to oxidized (GSSG) glutathione in the chloroplasts. An increased GSH/GSSG ratio protected RCA from proteolytic digestion and increased the stability of redox-sensitive enzymes in the chloroplasts. These results strongly suggest that BRs are capable of regulating the glutathione redox state in the chloroplasts through the activation of the ascorbate-glutathione cycle. The resulting increase in the chloroplast thiol reduction state promotes CO(2) assimilation, at least in part, by enhancing the stability and activity of redox-sensitive photosynthetic enzymes through post-translational modifications.
油菜素内酯（BRs）在植物生长、发育、光合作用和胁迫耐受中发挥着重要作用；然而，BR 增强光合作用的机制目前尚不清楚。在这里，我们提供的证据表明，BR 水平的增加提高了 PSII 的量子产率、Rubisco 激活酶（RCA）和果糖-1,6-二磷酸酶（FBPase）的活性，以及 CO2 的同化。BRs 上调了叶绿体中参与抗坏血酸-谷胱甘肽循环的基因的转录水平和酶的活性，导致叶绿体中还原型（GSH）与氧化型（GSSG）谷胱甘肽的比例增加。增加的 GSH/GSSG 比值保护 RCA 免受蛋白水解消化，并增加了叶绿体中氧化还原敏感酶的稳定性。这些结果强烈表明，BRs 能够通过激活抗坏血酸-谷胱甘肽循环来调节叶绿体中的谷胱甘肽氧化还原状态。由此增加的叶绿体硫醇还原状态通过翻译后修饰增强氧化还原敏感的光合作用酶的稳定性和活性，从而促进 CO2 的同化，至少在一定程度上是如此。
