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.

Cucumber (Cucumis sativus L.) lateral branch elongation is influenced by a variety of environmental signals, including light [e.g., far-red (FR) light] and hormones. In this experiment, the effect of FR light on the lateral branch elongation of cucumber (‘Zhongnong No. 26’) seedlings was investigated. The results showed that FR light significantly inhibited the lateral branch elongation of cucumber seedlings. In addition, FR light significantly increased the auxin (indole-3-acetic acid, IAA) content, decreased the cytokinin (CTK; Zeatin) content, and suppressed the expression of most CTK synthetic-related genes, such as IPTs, in cucumber seedlings. The lateral branch elongation of cucumber seedlings was assessed in response to decapitation and exogenous 6-BA treatment to further investigate the relationship between IAA and CTK on the lateral branch elongation of cucumber seedlings under FR light. Both decapitation and exogenous 6-BA treatment eliminated the inhibitory effect of FR light on the lateral branch elongation of cucumber seedlings. In conclusion, these results indicated that IAA and CTK were involved in the regulatory effects of FR light on cucumber seedling lateral branch elongation.