Department of Ecological and Biological Sciences, University of Tuscia , Largo dell'Università, snc, 01100 Viterbo, Italy.
J Proteome Res. 2013 Nov 1;12(11):4979-97. doi: 10.1021/pr400793e. Epub 2013 Oct 8.
Among heavy metal stressors, cadmium (Cd) pollution is one leading threat to the environment. In this view, research efforts have been increasingly put forward to promote the individuation of phytoextractor plants that are capable of accumulating and withstanding the toxic metals, including Cd, in the aerial parts. We hereby adopted the hyperaccumulator B. juncea (Indian mustard) as a model to investigate plant responses to Cd stress at low (25 μM) and high (100 μM) doses. Analytical strategies included mass-spectrometry-based determination of Cd and the assessment of its effect on the leaf proteome and metabolome. Results were thus integrated with routine physiological data. Taken together, physiology results highlighted the deregulation of photosynthesis efficiency, ATP synthesis, reduced transpiration, and the impairment of light-independent carbon fixation reactions. These results were supported at the proteomics level by the observed Cd-dependent alteration of photosystem components and the alteration of metabolic enzymes, including ATP synthase subunits, carbonic anhydrase, and enzymes involved in antioxidant responses (especially glutathione and phytochelatin homeostasis) and the Calvin cycle. Metabolomics results confirmed the alterations of energy-generating metabolic pathways, sulfur-compound metabolism (GSH and PCs), and Calvin cycle. Besides, metabolomics results highlighted the up-regulation of phosphoglycolate, a byproduct of the photorespiration metabolism. This was suggestive of the likely increased photorespiration rate as a means to cope with Cd-induced unbalance in stomatal conductance and deregulation of CO2 homeostasis, which would, in turn, promote CO2 depletion and O2 (and thus oxidative stress) accumulation under prolonged photosynthesis in the leaves from plants exposed to high doses of CdCl2. Overall, it emerges that Cd-stressed B. juncea might rely on photorespiration, an adaptation that would prevent the over-reduction of the photosynthetic electron transport chain and photoinhibition.
在重金属胁迫中，镉（Cd）污染是对环境的主要威胁之一。在这种情况下，研究工作越来越多地提出促进能够积累和耐受包括 Cd 在内的有毒金属的超积累植物的个性化，我们采用超积累植物芥菜（印度芥菜）作为模型，研究植物对低（25 μM）和高（100 μM）剂量 Cd 胁迫的反应。分析策略包括基于质谱的 Cd 测定及其对叶片蛋白质组和代谢组的影响评估。结果与常规生理数据相结合。总的来说，生理结果突出了光合作用效率、ATP 合成、蒸腾减少和非依赖光的碳固定反应受损的失调。在蛋白质组学水平上，这些结果得到了支持，观察到 Cd 依赖性光合作用组件的改变和代谢酶的改变，包括 ATP 合酶亚基、碳酸酐酶和参与抗氧化反应（特别是谷胱甘肽和植物螯合肽稳态）和卡尔文循环的酶。代谢组学结果证实了能量产生代谢途径、硫化合物代谢（GSH 和 PCs）和卡尔文循环的改变。此外，代谢组学结果突出了磷酸甘油酸的上调，这是光呼吸代谢的副产物。这表明光呼吸速率可能增加，作为应对 Cd 诱导的气孔导度失衡和 CO2 稳态失调的一种手段，这反过来又会促进叶片光合作用延长时 CO2 的消耗和 O2（从而导致氧化应激）的积累，植物暴露在高剂量的 CdCl2 下。总的来说，Cd 胁迫下的芥菜可能依赖于光呼吸，这种适应可以防止光合作用电子传递链的过度还原和光抑制。
