Mitigation of copper toxicity by calcium and citrate involves the modulation of ascorbate-glutathione cycle and redox status in pisum sativum l. Seedlings

The aim of this study was to investigate the impacts of exogenous calcium (Ca) and citrate treatments in the shoots of copper (Cu)-treated pea seedlings. Seeds were germinated in distilled water or aqueous solutions of CuCl₂ (200 µM) for 3 days then in water or Cu or Cu+effectors (CaCl₂ or citrate-Na) for another 3 days.  The oxidative damages caused by exposure to Cu were reduced by simultaneous application of the metal and Ca or citrate, which were associated with increased Cu accumulation, elevated levels of hydroxyl radicals and superoxide anions and the increased superoxide dismutase and glutathione S-transferase activities. Concomitantly, exposure to Cu decreased the levels of the non-enzymatic antioxidant compounds, glutathione, ascorbate, and cysteine. However, Cu treatment induced a strong increase in enzyme activities associated with the glutathione-ascorbate cycle, namely ascorbate peroxidase (APX), monodehydroascorbate (MDHAR) reductase, and glutathione reductase (GR). Contrariwise, co-treatment of Cu with Ca or citrate eliminated the Cu-imposed increase in antioxidant enzyme activities. The profiles of 1-D and 2-D proteomics revealed that Cu-induced modifications of protein thiols and carbonyl groups. The present investigation demonstrated that Ca and citrate are efficient in minimizing oxidative damages under Cu stress, by regulating the antioxidant defense system, and maintaining a high status of the glutathione-ascorbate cycle.