Contamination of Cadmium (Cd) to agroecosystems through anthropogenic activities resulting in increased levels of Cd in food staffs is a decisive threat to public health. Phytohormone application has the potential to overcome Cd toxicity in plants ensuring food safety. This study examined the efficacy of the exogenous application of salicylic acid (SA) and methyl jasmonate (MeJA) to ameliorate the negative impacts of Cd toxicity at whole plant levels in spinach. The spinach (cv. Sathi) seeds were primed with two levels of each of SA (100 and 250 mu M) and MeJA (2.5 and 5 mu M) and grown in six hydroponic conditions such as (i) Control, (ii) Cd (10 mu M CdCl2.H2O), (iii) Cd + 100 mu M SA, (iv) Cd + 250 mu M SA, (v) Cd + 2.5 mu M MeJA and (vi) Cd + 5.0 mu M MeJA following completely randomized design with three replications. Respected concentrations of Cd, SA and MeJA were diluted in the nutrient solution of the hydroponic tanks at 14 days after sowing and allowed to grow the spinach plants for three weeks. Cd stress significantly hindered spinach growth, stomatal conductance, transpiration rate, quantum yield of photosystem-II, electron transport rate, and pigment contents; triggered malondialdehyde (MDA) and H2O2 production and exhibited enhanced activities of superoxide dismutase (SOD), catalase (CAT) and guaiacol peroxidase (GPX) enzymes. All these impaired growth and physio-chemical attributes induced by Cd exposure were ameliorated by the exogenous application of SA and MeJA in both levels. Among treatments, 100 mu M SA and 5 mu M MeJA greatly increased total dry weight by 75% and 72%, respectively compared to individual Cd treatment. Furthermore, Cd-induced MDA and H2O2 contents in leaves were reduced by 100 mu M SA (39% and 30%) and 5 mu M MeJA (48% and 30%), respectively. The activities of SOD, CAT and GPX enzymes in spinach leaves were increased by 32%, 64% and 62% for 100 mu M SA and by 64%, 42% and 50% for 5 mu M MeJA application, respectively. Moreover, significant reduction in total Cd content (51%, 34%, 45% and 57%) was apparent in SA (100 and 250 mu M) and MeJA-treated (2.5 and 5 mu M) plants, respectively. Supplementation of SA and MeJA effectively mitigated the toxicity, uptake and translocation of Cd by modulating growth, physiology and redox regulation in spinach plants. The study recommends the exogenous application of 100 mu M SA and 5 mu M MeJA for the mitigation of Cd stress in spinach plants in Cd-contaminated areas with further field trials.
