Effects Of Exogenous Melatonin In The Germination And Seedling Growth Of Bermudagrass Under Lead Stress Treatments

As researchers continue to deepen the study of plant tolerance to heavy metal pollution,the application of plant endogenous hormones to enhance plant tolerance has gradually become a research hotspot.Studies have shown that the application of exogenous melatonin can enhance the ability of plants to withstand drought,high temperatures,cold and other adverse conditions.However,there are few studies on the enhancement of turfgrass plant tolerance to heavy metal pollution by melatonin.Therefore,in this experiment,the bermudagrass,one of the world’s three warm-season turfgrasses,was selected as the research material,and the heavy metal Pb was used as the pollution factor to investigate the tolerance of seeds and seedlings to Pb-contaminated soil under different lead concentrations.By applying different concentrations of MT,to improve the lead tolerance of bermudagrass through the antioxidant system.（1）When the concentration of heavy metal Pb is higher than 500mg/kg,it causes obvious damage to the Bermudagrass seeds,which makes the germination rate lower and even hard to germinate.Under the Pb stress of 500 mg/kg,different concentrations of melatonin pretreatment were carried out,and the germination rate was significantly improved.Melatonin pretreatment can increase the activity of antioxidant enzymes（POD,SOD）,thereby reducing the degree of membrane lipid peroxidation（reduced MDA content）,increasing chlorophyll content and biomass.The sorting effect of exogenous melatonin in different concentrations was 20μmol/L>50μmol/L>5μmol/L>100μmol/L.Therefore,the optimal pretreatment concentration was 20μmol/L.（2）Under the Pb stress of 1000mg/kg and 2000mg/kg,exogenous pretreatment of20umol/L and 100umol/L melatonin can effectively alleviate Pb stress on bermudagrass by increasing antioxidant enzyme activity and non-enzymatic antioxidant content,reduced membrane peroxidation and increased biomass.The bermudagrass with lead stress showed leaf languished and increased ROS content.Pretreatment concentrations of 20μmol/L and100umol/L melatonin significantly increased the activity of antioxidant enzymes（SOD,POD,CAT,APX and GR）and non-enzymatic antioxidants（AsA and GSH）in bermudagrass seedlings.Thereby,the accumulation of active oxygen(H₂O₂ and O^2-)was reduced,and finally the degree of membrane lipid peroxidation and cell permeability were lowered.These changes helped maintain the relative water content of the roots of bermudagrass under lead stress,promoted the synthesis of chlorophyll and increased the accumulation of biomass.The optimum concentration of melatonin for the roots of bermudagrass under heavy metal stress:20μmol/L.The high concentration of melatonin relieved Pb and played a significant role in the stress of bermudagrass seedlings.（3）Under the Pb stress of 1000mg/kg,20μmol/L melatonin was used to pretreat the bermudagrass seedlings,and the tolerance of grass to lead stress was enhanced by regulating glutathione content and glyoxalase system.Exogenous melatonin enhances the photosynthetic pigment and soluble protein content by increasing the biomass of bermudagrass,while reducing the relative conductivity,ensuring cell membrane permeability and maintaining osmotic balance.While increasing glutathione content（GSH,GSSG and GSSG/GSH）,the activity of Gly I and Gly II was increased to reduce the toxicity of MG and ROS to plants,thereby enhancing the lead tolerance of bermudagrass.