Effects Of Autotoxic Substance On The Growth Of Pepper Seedlings And Physiological Mechanism Of MT Alleviating DEP Stress

Pepper has always been the characteristic economic vegetable crop in Jiangxi province,which has important practical significance for increasing farmers'income.But autotoxicity is one of the important causes of pepper continuous cropping obstacles.As autotoxin stress is a kind of abiotic stresses,and previous studies have suggested that melatonin?MT?can enhance the antioxidant capacity of plants under abiotic stress,thus reducing the damage of abiotic stress on plants.However,there are few studies on MT induced resistance of pepper to autotoxic stress.In this study,Xinxiang 8,a pepper variety with large cultivation area in Jiangxi province,was used as the experimental material,and pepper autotoxic substances are considered as abiotic stress substances.To investigate the effect of autotoxicant on the growth of pepper seedlings,and the physiological mechanism of applying MT to the leaves and roots to alleviate the growth of pepper seedlings under the stress of diethyl phthalate?DEP?.The main research results are as follows:1?The effects of diethyl phthalate?DEP?,diisobutyl phthalate?DIBP?,2,6-ditert-butyl phenol?2,6-DTBP?and vanillin?Va?on seed germination of capsicum were studied.The results showed thatThe order of the toxicity of the four substances on the germination of pepper seeds was 2,6-DTBP>DEP>DIBP>Va.2?The effects of diethyl phthalate and 2,6-ditert-butylphenol on the growth of pepper seedlings were investigated.The results showed that High concentration of DEP and2,6-DTBP inhibited root mean diameter,total root length,total root surface area,total root volume and total root tip number,decreased chlorophyll content,and increased electrolyte exudation rate and MDA content.The toxic effects of DEP and 2,6-DTBP on pepper seedlings were different.3?Explore the effect of leaf MT application on antioxidant system of pepper leaves under DEP stress.The results showed that under the stress of 2 mmol·L^-11 DEP,the CAT,POD and SOD activities of pepper seedlings were significantly enhanced,GSH content was decreased,H₂O₂ and MDA content were significantly accumulated.MT pretreatment further enhanced the enzyme activity of leaves under DEP stress,GSH content was also increased,H₂O₂ and MDA content was reduced.It has positive significance to relieve the stress of pepper DEP.4?Explore the effect of MT applied from the root on the antioxidant enzyme system of pepper leaves under DEP stress,The results showed thatpretreatment with 1?mol·L^-1MTof roothad certain stimulating effect on the antioxidant system of pepper under DEP stress,that is,it can significantly enhance the activity of CAT,SOD and APX,increase GSH content,and aslo reduce the levels of H₂O₂ and MDA.It has positive significance to relieve the stress of pepper DEP.5?The effects of foliar application of MT on the antioxidant system of pepper leaves under DEP stress were studied under the condition of inhibition of endogenous reduced glutathione?GSH?synthesis.The results showed that spraying MT treatment on the leaves of GSH-producing pepper seedlings can induce the enhancement of antioxidant enzyme activities of pepper seedlings under DEP stress,significantly reduce H₂O₂ and MDA content in leaves,and increase GSH content.When the GSH synthesis of pepper seedlings was inhibited,the antioxidant enzyme activity of pepper leaves decreased,the GSH content decreased sharply,and the contents of H₂O₂ and MDA increased significantly.At this time,spraying MT on the leaves of pepper could not stimulate the activity of antioxidant enzymes in pepper leaves under DEP stress,nor could it reduce the content of H₂O₂ and MDA in leaves,and could not increase the content of GSH.