Abstract:

Orchard grass （Dactylis glomerata） is a world famous temperate cold-season forage grass. In recent years， frequent floods in southern China have seriously affected forage crop production. In order to explore the response mechanism of orchard grass roots under submergence stress， the waterlogging-tolerant orchard grass cultivar ‘Dianbei’ （DB） and the waterlogging-sensitive orchard grass cultivar ‘Anba’ （AB） were studied. Two waterlogging treatments （8 and 24 h） were set up， and a non-waterlogging treatment was used as the control （0 h）. The morphology was observed and metabolomics analysis was performed on the seedling roots for 0， 8 and 24 h treatments. It was found that the root growth of the two varieties became weak and the roots became black after submergence stress treatment， and adventitious roots were produced by cultivar DB after treatment for 24 h. 120 differentially produced metabolites were identified in the DB_8h vs DB_0h comparison and 155 differentially produced metabolites were identified in the DB_24h vs DB_0h comparison， while 93 differentially produced metabolites were identified in the AB_8h vs AB_0h comparison and 118 differentially produced metabolites were identified in the AB_24h vs AB_0h comparison. Between cultivars， 80 differentially produced metabolites were identified in the DB_0h vs AB_0h comparison； 125 differentially produced metabolites were identified in the DB_8h vs AB_8h comparison and 48 significantly differentially produced metabolites were identified in the DB_24h vs AB_24h group. Six flavonoids involved in the metabolic pathway of flavonoid biosynthesis were found in the waterlogging-tolerant orchard grass cultivar DB， namely： Hesperidin， glycyrrhizin， apigenin， neohesperidin， naringin and naringenin； While four amino acids and their derivatives were found in the waterlogging-sensitive orchard grass cultivar， namely： O-phosphate-L-serine， L-glutamic acid， L-tyrosine and tryptophan. These amino acids are involved in the metabolic pathway of amyl-tRNA biosynthesis； Glycine， serine and threonine metabolism； Glucosinolate biosynthesis； Phenylalanine， tyrosine and tryptophan biosynthesis and the tryptophan metabolic pathway. Comparison of the differential metabolites of DB and AB under the same duration of flooding stress indicated that the main differentially produced metabolites present in DB were sucrose， isomaltose， alginate 6-phosphate， L-ornithine， L-histidine， D-ornithine and apigenin， and the metabolic pathways involved were ABC transport factor， starch and sucrose metabolism， β-alanine metabolism flavonoid biosynthesis and flavonoid and flavonol biosynthesis. These differentially produced metabolites may be responsible for the differences in waterlogging tolerance between the two species. The results provide a basis for resolving the differentially produced metabolites and metabolic pathways in orchard grass in response to submergence stress， and provide a reference for further studies on the molecular mechanisms of orchard grass metabolic regulation in response to submergence stress.

Key words: orchard grass, submergence stress, metabolomics, differential metabolites, metabolic pathways