Nickel Ions Enhanced the Adaptability of Tomato Seedling Roots to Low-Nitrogen Stress by Improving Their Antioxidant Capacity

Abstract

To elucidate the physiological mechanisms underlying the impact of exogenous nickel ions (Ni2+) on the adaptability of tomato (Solanum lycopersicum L.) seedling roots to low-nitrogen levels, the cultivar ‘Micro Tom’ was selected as the experimental material and cultivated hydroponically in the cultivation room of the Fujian Agriculture and Forestry University. Two distinct nitrogen concentrations (7.66 and 0.383 mmol·L−1) and two different levels of Ni2+ (0 and 0.1 mg·L−1 of NiSO4·6H2O) were employed as treatments. On the 9th day of cultivation, we measured the root biomass, the concentrations of antioxidant compounds, and the activities of antioxidant enzymes in the tomato seedlings. The study showed that when the nitrogen levels were low, the growth and development of the tomato seedling roots were hindered. This led to a significant increase in the levels of hydrogen peroxide (H2O2), superoxide anion (O2−), and malondialdehyde (MDA), indicating oxidative damage to the roots. Conversely, treatment with Ni2+ induced a notable increase in the activity of antioxidant enzymes in the seedlings and augmented the accumulation of nonenzymatic antioxidants, such as ascorbic acid (ASA) and reduced glutathione (GSH), thereby enhancing the operational efficiency of the ascorbate–glutathione cycle (ASA–GSH). Consequently, this led to substantial reductions in the H2O2 and MDA levels, ultimately mitigating the oxidative damage inflicted on the tomato seedling roots subjected to low-nitrogen stress. In conclusion, exogenous Ni2+ can reduce the peroxidative damage of tomato seedlings by promoting antioxidase activity in tomato seedlings under low-nitrogen stress, improve the tolerance of tomato seedlings to low-nitrogen stress, and maintain the normal growth and development of tomato seedlings.