Mechanism Of DIMBOA Alleviating Autotoxic Effects Of Coumarin In Alfalfa(Medicago Sativa L.)

The continuous cropping disorder dominated by autotoxicity has become the bottleneck of alfalfa（Medicago sativa L.）intensive production.Corn（Zea mays L.）is the most suitable crop for rotation with alfalfa from the allelopathy perspective.DIMBOA（2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one）is the main allelopathic substances in corn.Therefore,it is important and significant for exploring whether DIMBOA can alleviate the effect of autotoxic substance stress on seed germination and seedling growth of alfalfa.In this study,we first exploring the allelopathic promoting effect of corn root exudates on alfalfa.Then,we choosing coumarin as the main autotoxic substance of alfalfa,and exploring the effects of the interaction between DIMBOA and coumarin on the growth and development and molecular level of alfalfa.Finally,the physiological and molecular mechanisms of DIMBOA in alleviating alfalfa seedling growth under coumarin stress were investigated.It provides a theoretical basis for the regulatory measures to guide alfalfa to overcome continuous cropping obstacles in production.The main results are summarized as follow:（1）Corn root exudates can promote the seeds germination of alfalfa by promoting seedling growth and simple viability index,it promoted the antioxidant capacity of alfalfa seedlings mainly by increasing the ascorbate（As A）and dehydroascrobate（DHA）content and reducing the malondialdehyde（MDA）content.（2）5 mg·L^-1 coumarin can cause the general inhibition of various indicators of alfalfa seeds and seedlings.0.6 m M DIMBOA promoted alfalfa seed germination and seedling growth and development.The addition of DIMBOA under coumarin stress can improve the growth and development of alfalfa by improving antioxidant capacity,root morphological characteristics,and photosynthetic ability.Moreover,DIMBOA mainly increases the Chlorophyll b（Chl b）content and the net photosynthetic rate（Pn）by increasing the ASA content and catalase（CAT）,peroxidase（POD）,ascorbate peroxidase（APX）activity,while reducing the MDA and superoxide anion free radical(O₂^·-)content,and increasing the root length,root average diameter and root volume to maintain redox balance,promote the growth and development and enhanced the photosynthetic ability of alfalfa seedlings,thereby improving the growth and development of alfalfa seedlings under coumarin stress.（3）Compared with coumarin treatment,the addition of DIMBOA under coumarin stress mainly changed the expression of related genes in the galactose metabolic pathway,enhanced the nitrogen cycle of alfalfa,increased the cutin,suberine and wax biosynthesis,promoted the expression of related genes in linoleic acid metabolism,and activated the effective antioxidant defense system.In particular,the expression of relevant genes in glutathione metabolism can participate in the stress resistance of plants by affecting nitrogen absorption,assimilation and amino acid metabolism,thereby alleviating the stress effect of coumarin.（4）Coumarin disrupts the stability of alfalfa cell membranes by downregulating SN-Glycero-3-phosphocholine in glycerophospholipid metabolism,thereby affecting its metabolism.The addition of DIMBOA under coumarin stress upregulated the expression of sn-glycero-3-phosphocholine,thereby increasing the stability of alfalfa cell membranes.The addition of DIMBOA under coumarin stress can inhibit the synthesis of coumarin by alfalfa by regulating the expression of the precursor substances（L-tyrosine and succinate）.