Castor, a non-food, dedicated bioenergy crop, has immense potential to be used for phytoremediation/revegetation of heavy metal contaminated sites. In the previous study, we identified arsenate [As(V)]-tolerant (WM) and As(V)-sensitive (GCH 2) genotypes of castor (Ricinus communis L.) with differential accumulation and tolerance of arsenic [As]. The role of thiols in As(V) toxicity and tolerance mechanism in the castor plant is not fully understood. On the one hand, thiol-dependent reduction of As(V) to As(III) by arsenate reductase (AR) makes it capable of reacting with thiol groups of protein leading to disturbed metabolic pathways; on the other hand, reduction of As(V) to arsenite [As(III)] by AR and then complexation of As(III) with phytochelatins (PCs) and compartmentalization of As(III)-PC complex are considered as the major detoxification mechanisms of As(V). In our study, the expression of RcAR increased in leaves and roots of As(V)-tolerant castor genotype WM but decreased in sensitive genotype GCH 2 due to 200 μM As(V) treatment. The activity of glutathione reductase (GR) increased significantly in the tolerant genotype, whereas it remained same in the sensitive genotype. GSH/GSSH ratio declined substantially in the sensitive genotype. The increased expression of phytochelatin synthase 1 isoform 1 (RcPCS1X1) in roots, RcPCS1X2 and metallothionein type 2 (RcMT2) in leaves, and c-type ABC transporter (RcABCC) in roots and leaves of WM was observed, but the expression of these genes declined or remained the same in GCH 2. Overall, our results suggest the essential roles of GR, RcAR, RcPCS1, RcMT2, and RcABCC in the tolerance of WM castor genotype to As(V) toxicity.

中文翻译：

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生物能源作物蓖麻耐受和敏感基因型中硫醇代谢和参与砷解毒基因的差异反应

蓖麻是一种非食用的专用生物能源作物，具有用于重金属污染场地的植物修复/重新植被的巨大潜力。在之前的研究中，我们确定了具有砷 [As] 差异积累和耐受性的蓖麻 (Ricinus community L.) 的砷酸盐 [As(V)] 耐受 (WM) 和 As(V) 敏感 (GCH 2) 基因型。硫醇在蓖麻植物中 As(V) 毒性和耐受机制中的作用尚不完全清楚。一方面，砷酸还原酶 (AR) 将 As(V) 还原为 As(III) 的硫醇依赖性使其能够与蛋白质的硫醇基团反应，从而导致代谢途径受到干扰；另一方面，通过 AR 将 As(V) 还原为亚砷酸盐 [As(III)]，然后 As(III) 与植物螯合素 (PC) 的络合以及 As(III)-PC 复合物的区室化被认为是 As(V) 的主要解毒机制）。在我们的研究中，由于 200 μM As(V) 处理，RcAR 在耐 As(V) 蓖麻基因型 WM 的叶和根中表达增加，但在敏感基因型 GCH 2 中降低。谷胱甘肽还原酶（GR）的活性在耐受基因型中显着增加，而在敏感基因型中保持不变。GSH/GSSH 比率在敏感基因型中大幅下降。观察到 WM 根中植物螯合素合酶 1 同种型 1 (RcPCS1X1)、叶中 RcPCS1X2 和金属硫蛋白 2 型 (RcMT2) 以及 c 型 ABC 转运蛋白 (RcABCC) 的表达增加，