Abstract: We investigated the effects of exogenous selenium (Se) and nitric oxide (NO) on the growth of tomato seedlings under drought stress using ‘Bojue II’ tomato as the test material in a hydroponic culture system. There were eight treatments under both control and drought stress conditions, comprising: no external substance application (ddH₂O), root-applied 1 μmol·L^-1 Se, foliar-sprayed 100 μmol·L^-1 NO, and their combined treatment. We measured tomato seedling growth, membrane lipid peroxidation, chlorophyll content, antioxidant enzyme activities, and the expression levels of related genes. Compared with the control (CK), drought stress significantly decreased the growth parameters and photosynthetic pigment contents of tomato seedlings while inducing oxidative damage, which was characterized by marked elevations in the levels of malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and the activities of antioxidant enzymes. Under drought stress, exogenous selenium (Se) and nitric oxide (NO) effectively mitigated oxidative damage, with the combined Se+NO treatment exerting the most pronounced effect. Relative to no exogenous addition treatment, the MDA and H₂O₂ contents in leaves were significantly reduced by 42.5% and 42.8%, respectively. The combined treatment downregulated oxidative stress and strongly activated the antioxidant defense system. Specifically, it increased the expression levels of SlSOD, SlCAT, SlAPX, and SlGR genes by 67.8%, 28.6%, 38.5% and 21%, respectively. This, in turn, further enhanced the activities of superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APX), and glutathione reductase (GR) by 140%, 20%, 30%, and 30%, respectively. In summary, exogenous Se and NO application improved photosynthetic performance and growth of tomato seedlings under drought stress by synergistically regulating the transcription of antioxidant enzymerelated genes, enhancing the activity of the enzymatic defense system, and alleviating membrane lipid peroxidation. This study provides a basis for elucidating the mechanisms underlying the effects of Se, NO, and their interaction, and offers theoretical support for their application in tomato production.

Key words: tomato, drought stress, selenium, nitric oxide, physiological characteristics