The Alleviation Effect Of Exogenous Melatonin And 2,4-Epibrassinolide On Saline-alkali Stress In Rosa Cymosa Tratt.

Rosa cymosa Tratt.,commonly used as a rootstock for cultivating tree-like roses,has the characteristics of shade tolerance,strong vitality,and robust root system.It exhibits strong resistance to diseases and pests,fast growth,strong upright habit,and high survival rate when grafted with roses.Previous studies conducted by our research group have shown that although Rosa cymosa Tratt.has a certain degree of salt-alkali tolerance,its growth is still affected under prolonged exposure to high concentrations of salt-alkali stress.Exploring methods to enhance the salt-alkali tolerance of Rosa cymosa Tratt.can expand the application scope of tree-like roses and improve the ornamental and greening aspects of salt-alkali landscapes.In recent years,it has been discovered that many exogenous substances can enhance the stress resistance of plants.Studies have shown that exogenous application of melatonin（MT）and 2,4-epibrassinolide（EBR）can increase the content of osmoregulators in plants,improve antioxidant enzyme activity,and enhance salt-alkali tolerance,thereby reducing stress-induced damage to plants.However,it is still unknown whether MT and EBR can improve the salt-alkali tolerance of Rosa cymosa Tratt.and at what concentrations.This study used two-year-old Rosa cymosa Tratt.cuttings as experimental materials and simulated a salt-alkali environment with Na Cl:Na₂SO₄:Na HCO₃:Na₂CO₃=1:9:9:1.The effects of different concentrations of exogenous MT and EBR on the photosynthetic characteristics,membrane system,antioxidant enzyme activity,and osmoregulator content of Rosa cymosa Tratt.under salt-alkali stress were investigated.The aim was to explore the alleviating effect of exogenous MT and EBR on the damage to Rosa cymosa Tratt.seedlings under salt-alkali stress and identify appropriate concentrations of MT and EBR.This would provide theoretical and technical support for improving the salt-alkali tolerance of Rosa cymosa Tratt.and expanding the application scope of Rosa cymosa Tratt.as a rootstock for roses.The main research conclusions are as follows:1.Salt-alkali stress significantly reduced the chlorophyll content and F_v/F_m value in Rosa cymosa Tratt.leaves,while increasing the content of MDA,relative conductivity,soluble sugar content,and the activities of SOD,POD,and CAT.2.Under salt-alkali stress,pretreatment with MT and EBR increased the PSⅡcontent and F_v/F_m value in Rosa cymosa Tratt.leaves.This indicates that exogenous MT and EBR can slow down the degradation of chlorophyll,enhance the activity of the PSⅡreaction center,improve the conversion and utilization efficiency of light energy,and effectively alleviate the damage to leaves caused by the decline in PSⅡ.3.Under salt-alkali stress,pretreatment with MT and EBR reduced the content of MDA and relative conductivity in Rosa cymosa Tratt.leaves,thus lowering the level of membrane lipid peroxidation,reducing electrolyte leakage,and protecting the integrity of cell membranes.This effectively alleviated the damage to Rosa cymosa Tratt.leaves caused by salt-alkali stress.4.Under salt-alkali stress,pretreatment with MT and EBR enhanced the activities of SOD,POD,and CAT,effectively inhibiting the production of reactive oxygen species in Rosa cymosa Tratt.leaves.By increasing the activity of antioxidant enzymes,it alleviated oxidative damage caused by salt-alkali stress and improved the resistance of Rosa cymosa Tratt.to stress.5.Under salt-alkali stress,pretreatment with MT and EBR increased the soluble sugar content in Rosa cymosa Tratt.leaves,reducing the cell’s osmotic potential.This created conditions for maintaining normal physiological metabolic activities in cells and enhanced the salt tolerance of Rosa cymosa Tratt.under salt stress.6.After applying different concentrations of MT and EBR to Rosa cymosa Tratt.under salt-alkali stress,physiological indicators showed varying degrees of increase or decrease compared to salt-alkali treatment alone,indicating differences in the effects of different concentrations of MT and EBR.Comprehensive evaluation through principal component analysis and membership function calculation revealed the ranking of the alleviating effects of different concentrations of MT and EBR on salt-alkali stress in Rosa cymosa Tratt.:300μmol·L^-1 MT>0.2 mg·L^-1 EBR>0.1 mg·L^-1 EBR>200μmol·L^-1 MT>0.4 mg·L^-1 EBR>400μmol·L^-1 MT.