Effects of exogenous nitric oxide (NO) on growth and physiological characteristics of Machilus yunnanensis seedlings under drought stress

Using sodium nitroprusside (SNP) as an exogenous nitric oxide (NO) donor, the effect of exogenous NO on the growth and physiological characteristics of Machilus yunnanensis seedlings under drought stress were investigated, it provides a theoretical basis for improving the drought resistance of landscape plants in urban green space under the current water shortage. The results showed that: ① Under drought stress, the relative water content of leaves (LRWC), the chlorophyll content (Chl) and the biomass and photosynthetic rate (P_n) in leaves of Machilus yunnanensis seedlings were significantly decreased, and the content of malondialdehyde (MDA) and the activities of antioxidant enzymes were significantly increased; ② after treatment with SNP, the contents of Chl, Pro, SP, SS of Machilus yunnanensis seedlings were increased, the LRWC, P_n and the biomass of Machilus yunnanensis seedlings were improved, and the activities of ascorbic acid peroxidase (APX), peroxidase (POD), catalase (CAT) of Machilus yunnanensis seedlings were enhanced, while the content of MDA was decreased significantly; ③ among all SNP treatments, the effect of foliar spraying was better than that of rhizosphere irrigation, among the foliar spray treatment group, 0.1 mmol/L SNP had the best effect, and the effect was weakened when the concentration of SNP was 0.2 mmol/L. The study showed that the growth and photosynthesis of Machilus yunnanensis seedlings were inhibited, the membrane lipid of Machilus yunnanensis seedlings was damaged under drought stress, drought stress also increased the root-shoot ratio (R/S), the osmotic adjustment substance content and the antioxidant enzymes activities of Machilus yunnanensis seedlings. The exogenous NO treatment further increased the osmotic adjustment substance content and the antioxidant enzymes activities of Machilus yunnanensis seedlings, and effectively enhanced drought resistance of Machilus yunnanensis, and maintained its biomass accumulation and normal growth under drought condition. The effect of exogenous NO is affected by the application method and concentration, at the appropriate concentration, it can significantly improve the drought resistance of Machilus yunnanensis seedlings.