Calcium and jasmonic acid exhibit synergistic effects in mitigating arsenic stress in tomato seedlings accompanied by antioxidative defense, increased nutrient accumulation and upregulation of glyoxalase system

No substantial information is available to explain the associative roles of calcium (Ca²⁺) and jasmonic acid (JA) in enhancing tolerance of plants to abiotic stresses. It is therefore, imperative to investigate the interaction of these biomolecules in plants subjected to heavy metal stress. The concomitant effects of Ca²⁺ and/or JA on the physiological mechanism associated with metalloid stress tolerance are still not substantially explored in tomato seedlings. Present study unveils the synergistic role of Ca²⁺ and JA in mitigation of arsenic toxicity (As) in tomato seedlings. Present evidence reveals that plant grown in As toxicity conditions exhibited a decrease in growth attributes (shoot length, shoot fresh weight and shoot dry weight) and supressed the biosynthesis mechanism of chlorophyll (Chl), nutrients homeostasis [Ca²⁺, nitrogen (N), phosphorus (P), and potassium (K)] and glyoxalase system. Exogenous As induced the over production of reactive oxygen species (ROS) and methylglyoxal (MG), and enhanced Chl degrading enzyme [chlorophyllase (Chlase) activity in tomato seedlings. However, exogenous application of Ca²⁺ and/or JA supressed the adverse effect of As. Moreover, combined application of Ca²⁺ and JA was found to be more effective than their individual effects to the seedlings. Application of Ca²⁺ and JA together significantly enhanced the biosynthesis of Chl by supressing Chlase activity and enhancing the δ-aminolevulinic acid dehydratase (δ-ALAD) activity (a Chl synthesising enzyme) and also improved activity of glyoxalase I (Gly I) and Gly II activity (responsible for the detoxification of MG). Exogenous supply of Ca²⁺ and JA maintained the balance supply of nutrients and glycine betaine in tomato seedlings under As toxicity conditions. Combined application of Ca²⁺ and JA supressed the overproduction of ROS by modulating activity of antioxidant enzymes, such as superoxide dismutase, ascorbate peroxidase and glutathione reductase. When Ca²⁺ and JA were supplied with the Ca²⁺-chelator EGTA (ethylene glycol-bis(b-aminoethylether)-N,N,N',N'-tetraacetic acid), the efficacy of Ca²⁺ was eliminated, confirming the participation of Ca²⁺ and JA in mitigation of As toxicity. Thus, it is evident that Ca²⁺ and JA together mediated As tolerance of tomato seedlings t by improving physiological defence mechanisms.