Role of calcium signaling in cadmium stress mitigation by indol-3-acetic acid and gibberellin in chickpea seedlings

Given the adverse impacts of heavy metals on plant development and physiological processes, the present research investigated the protective role of indole-3-acetic acid (IAA) and gibberellic acid (GA3) against cadmium (Cd)-induced injury in chickpea seedlings. Therefore, seeds germinated for 6 days in a medium containing 200 mu M Cd alone or combined with 10 mu M GA3 or 10 mu M IAA. Both GA3 and IAA mitigated Cd-imposed growth delays in roots and shoots (80% and 50% increase in root and shoot length, respectively). This beneficial effect was accompanied by a significant reduction in Cd2+ accumulation in both roots (74% for IAA and 38% for GA3) and shoots (68% and 35%, respectively). Furthermore, these phytohormones restored the cellular redox state by reducing the activity of NADPH oxidase and downregulating the transcription level of RbohF and RbohD genes. Likewise, hydrogen peroxide contents were reduced by GA3 and IAA supply. Additionally, GA3 and IAA countered the Cd-induced reduction in total phenols, flavonoids, and reducing sugars in both roots and shoots. The exogenous effectors enhanced the activities of catalase, ascorbate peroxidase, and thioredoxin, as well as the corresponding gene expressions. Interestingly, adding GA3 and IAA to the Cd-contaminated germination media corrected the level of calcium (Ca2+) ion within seedling tissues. This effect coincided with the upregulation of key genes associated with stress sensing and signal transduction, including auxin-binding protein (ABP19a), mitogen-activated protein kinase (MAPK2), calcium-dependent protein kinase (CDPK1), and calmodulin (CaM). Overall, the current results suggest that GA3 and IAA sustain the Ca2+ signaling pathway, resulting in metal phytotoxicity relief. Amendment of agricultural soils contaminated with heavy metals with GA3 or IAA could represent an effective practice to improve crop yield.