Exogenous calcium repairs damage caused by nickel toxicity in fenugreek (Trigonella foenum-graecum L.) by strengthening its antioxidant defense system and other functional attributes.

• Nickel at 80 mg kg−1 of soil showed deleterious effects on fenugreek plants. • Calcium application showed encouraging effects on the Ni-affected plants. • Calcium successfully repairs the damage caused by Ni toxicity in plants. • Calcium significantly enhanced all growth & physiological attributes under Ni stress. Nickel (Ni) toxicity has a wide range of metabolic effects on plants, and various anatomical and morphological modifications occur that consequently diminish growth and productivity of plants. Different means of nutrient delivery in plants are being used to combat the harmful effects of Ni stress. The purpose of this study was to determine how the fenugreek plant (Trigonella foenum-graecum L.) responds to exogenous supplementation of calcium (Ca) in stress free and stressed conditions (Ni stress). The plants were supplemented with different concentrations of calcium (0, 40, 80, 120 and 160 mg kg−1) as CaCl 2 under Ni stress. The selected concentration of Ni was applied in the form of NiCl 2 with 80 mg kg−1 of soil to the plants and one set was kept as control. Nickel applied at highest concentration (80 mg kg−1) exhibited maximum inhibition in most of the parameters studied. In this study, Ni at 80 mg kg−1 reduced all the growth attributes (shoot and root lengths, plant fresh and dry weights and leaf area) as well as physiological attributes (chlorophyll (Chl) and carotenoid (Car) content, maximum quantum efficiency (Fv/Fm), carbonic anhydrase (CA) and nitrate reductase (NR) activities). The antioxidant enzymes viz. superoxide dismutase (SOD), catalase (CAT), peroxidase (POX), and other oxidative stress markers such as hydrogen peroxide (H 2 O 2), malondialdehyde (MDA) content, proline (PRO) content and electrolyte leakage (EL) substantially increased as compared to the control in Ni-exposed plants. However, all growth characteristics as well as the level of other functional attributes viz. Chl, Car, fv/fm, CAT, POX, and SOD, PRO, H 2 O 2 , MDA and EL improved significantly in plants supplied with CaCl 2 at 120 mg kg−1 of soil The exogenous application of Ca exhibited a significant and synergistic effect on the overall growth and physiological and metabolic processes of the plant without stress. Furthermore, exogenously-applied Ca also proved effective in countering Ni toxicity and protected fenugreek plant by strengthening antioxidant defense system and other factional attributes. [ABSTRACT FROM AUTHOR]