Induction of nickel resistance by sodium nitroprusside in tomato plant

The accumulation of heavy metals throughout the ecosystem is now a major environmental problem that threatens the quality of life of all living organisms. In a factorial experiment based on a completely randomized design, the effect of sodium nitroprusside on the physiological and biochemical responses of tomatoes under nickel stress was investigated. Tomato plants were grown in two concentrations of sodium nitroprusside (zero and 100 µM) and three different nickel concentrations (zero, 25, and 50 µM) with three replications under hydroponic conditions. The results showed that 50 μM nickel sulfate without sodium nitroprusside significantly reduced the relative water content of leaves (43.1%) compared to the same treatment with-sodium nitroprusside. An increase in electrolyte leakage and malondialdehyde were observed as an indicator of oxidative damage in plants under nickel sulfate stress. In response to oxidative stress caused by nickel sulfate, the amount of chlorophyll decreased and carbohydrate and proline concentrations increased compared to the control. Application of sodium nitroprusside resulted in higher concentrations of chlorophyll b (4.54%) and total chlorophyll (3.57%) under non-nickel sulfate stress than the control. Antioxidant, peroxidase, and catalase activity increased by 62, 37, and 38%, respectively, under nickel sulfate stress when treated with 100 µM sodium nitroprusside compared to non-sodium nitroprusside treatment. According to the results, sodium nitroprusside at a concentration of 100 µM can reduce the negative effects of nickel exposure on the growth characteristics of tomato plants such as the number of leaves and dry weight of the plant, by increasing the antioxidant activity (increasing the activity of the enzymes catalase and peroxidase) and also the positive effect of proline accumulation on the RWC, so the use of this substance is recommended for tomato plants growing under nickel conditions.