Effects of Brassinolide on Growth, Photosynthetic Rate and Antioxidant Enzyme Activity of Ornamental Gourd under Salt Stress

Abstract Salt stress has an important influence on the growth and development of gourd (Lagenaria siceraria (Molina) Standl.), and it is one of the abiotic factors that inhibit plant growth. As a plant growth regulator, brassinolide has a regulatory effect on plants under salt stress. In this study, “Yayao” gourd was treated with 85 mmol/L NaClstress to study the alleviation effect of different concentrations of brassinolide on ornamental gourd. The results showed that the concentration of brassinolide at 0.208 μmol/L under salt stress significantly increased the net photosynthetic rate, transpiration rate, stomatal conductance and chlorophyll content, regulated fluorescence parameters, and improved plant height, dry and fresh weight and root vigor of gourd seedlings under salt stress. Brassinolide increased soluble sugar content, decreased free proline content, promoted antioxidant enzymes (SOD, APX, CAT) activity, eliminated reactive oxygen species (ROS) damage, reduced malondialdehyde (MDA) accumulation, maintained cell expansion pressure, improved cell-environment osmoregulation, and inhibited membrane lipid peroxidation in gourds. In addition, salt stress increased the content of phenolic compounds, flavonoids, and lignin, and brassinolide further increased the content, which alleviated the damage of salt stress. The above analysis showed that salt stress had a certain effect on the physiological indexes of gourd seedlings, and the appropriate concentration of brassinolide could alleviate the damage of salt stress on gourd seedlings from several aspects.