Effects of calcium and EGTA on thiol homeostasis and defense-related enzymes in Cd-exposed chickpea roots

Exposure of chickpea seeds (Cicer arietinum L.) to cadmium stress for 6 days resulted in growth reduction and oxidative stress installation as exemplified by a strong accumulation of H₂O₂ and a disruption of enzymatic and non-enzymatic defense systems. The enrichment of the seed germinating medium with calcium and ethylene glycol tetraacetic acid (EGTA) relieved the detrimental effect of Cd on root growth. This protective effect would be the result of (1) protein thiol protection, as evidenced by thioredoxin system activation, and of (2) the glutathione disulfide content decrease. The absence of corrective effect of effectors on glutathione redox state should be associated with the concomitant decrease in regeneration and consumption processes of reduced forms of glutathione, namely by glutathione reductase and glutathione peroxidase activities, respectively. Calcium and EGTA application led to oxidative stress alleviation as evidenced by H₂O₂ content decrease and the restoration of catalase and ascorbate peroxidase activities at a level similar to control roots. Moreover, the analysis of the transcriptional system relating to the up-cited enzymes revealed a decreased gene expression subsequent to the enrichment of germination medium with the effectors. The present research provided deeper insights into the mechanisms induced by Ca and EGTA to protect plant cell against Cd-induced oxidative injury.