Exogenous Oxalic Acid Protects Germinating Chickpea Seeds Against Cadmium Injury

The objective of the present study was to elucidate the mechanism by which oxalic acid (OA) alleviates cadmium (Cd) stress. Chickpea (Cicer arietinum L.) seeds were treated with 200 µM CdCl₂ for 6 days or 3 days followed by the combination 200 µM Cd + 100 µM OA for three additional days. Exogenous OA mitigated the growth inhibition by Cd of both roots and shoots. This positive effect can be attributed to the increased OA exudation from roots and the alleviation of the Cd-induced depletion of endogenous OA in shoots (80% increase versus Cd-stressed). The combination Cd + OA proved to be effective in protecting cell membrane integrity. This beneficial effect was reflected by 36 and 24% decrease in lipoxygenase (LOX) activity in roots and shoots, respectively, and 60% decrease in the accumulation of the harmful aldehyde, 4-hydroxy-2-nonenal (4-HNE) in roots when compared to Cd-treated samples. Besides, OA restored the Cd-imposed disruption of the plasma membrane function. This effect was depicted by an optimal H⁺-ATPase activity and proton exudation rate. Oxalic acid counteracted the Cd-induced overproduction of hydroxyl radical (OH•) and NADPH-oxidase activity increase, leading to restore a steady cellular redox state. Furthermore, OA modulated the impact of Cd on Cu/Zn-superoxide dismutase (Cu/Zn-SOD), ascorbate peroxidase (APX), and catalase (CAT) activities in chickpea seedlings. Present results indicate that OA is able to alleviate Cd toxicity by protecting plasma membrane integrity and modulating antioxidant activities. Moreover, our findings shed light on the interplay between plasma membrane H⁺-ATPase and the accumulation and root exudation of OA.