Abstract: The aim of this research was to investigate the effect on seedling morphology and physiological characteristics of foliar uniconazole spraying of ‘Yumi 3’ proso millet seedlings under salt stress. Leaf photosynthetic characteristics, seedling growth and seedling antioxidase systems were measured, following foliar spraying with uniconazole (50 mg·L^-1), in plants grown under 150 mmol·L^-1 NaCl stress in sand culture experiments. The results showed that foliar uniconazole spraying increased net photosynthetic rate, transpiration rate, stomatal conductance and intercellular CO₂ concentration, maximum light energy conversion efficiency, actual photochemical efficiency and photochemical quenching of the seedlings, but decreased non-photochemical quenching coefficient. In seedlings exposed to salt stress and foliar spraying with uniconazole, seedling height decreased significantly (P<0.05), and leaf area and shoot dry weight also decreased. However, the total root length, root volume, root surface area, root average diameter and root dry weight of seedlings increased. With respect to antioxidase systems, in seedlings treated with uniconazole under salt stress, superoxide dismutase activity, peroxidase (POD) activity, catalase activity and soluble protein content were all increased, while malondialdehyde content and superoxide anion content ($\mathop{}_{A}^{B}$) were decreased. Among these parameters, POD activity and $\mathop{}_{A}^{B}$ levels showed no significant differences in leaves, but significant differences in roots (P<0.05). Therefore, foliar uniconazole (50 mg·L^-1) spraying at the three-leaf-and-one-leaflet stage of development effectively improved the salt tolerance of proso millet seedlings by regulating the seedling morphological characteristics, enhancing the protective enzyme activity and soluble protein content in the roots and leaves, and decreasing the degree of membrane lipid peroxidation.

Key words: uniconazole, proso millet, leaf, root, morphology, physiological property