The Study On Metabolism Of Fatty Acids Of Astragalus Membranaceus Seeds During Seedling Morphology

Astragalus membranaceus(A.membranaceus),a traditional Chinese medicinal plant,has more than 2000 years medicinal history.The process of A.membranaceus from seed germination to seedling morphogenesis is the process of its transformation from seed feeding to photosynthesis support,and it is also a relatively fragile stage in its life history in the face of environmental changes.In this paper,the seeds of A.membranaceus were used as material to study the metabolic changes of storage reserves including fatty acids during seed germination and morphogenesis.At the same time,the changes of active substances such as flavonoids and saponins of A.membranaceus seedlings during morphogenesis were also studied.It is expected to provide a reference for further understanding of seed storage reserves metabolism of A.membranaceus on seed germination and morphogenesis.The main results are as follows:During the seed germination and post-germination growth of A.membranaceus,it was found that the starch stored in the cotyledons was preferentially utilized,while the lipid was mainly mobilized during the post-germination growth.The analysis of fatty acid compositions showed that the proportion of the main saturated and monounsaturated fatty acids in the cotyledons was reduced,whereas the polyunsaturated fatty acids were the opposite,but the overall change was small.Exogenous abscisic acid and methyl jasmonate inhibited the germination and later growth of A.membranaceus seeds.At the same time,abscisic acid and methyl jasmonate inhibited the mobilization of storage reserves,reduced its utilization efficiency,led to high consumption of carbon in storage reserves at early stage,and prevented the desaturation of fatty acids in cotyledons and the elongation of carbon chain.In the process of morphogenesis of A.membranaceus seedlings,it was found that the fatty acid compositions in the cotyledons had undergone significant changes.Compared with skotomorphogenesis,the proportion of alpha-linolenic acid in cotyledons increased by 28.62%under light,while oleic acid decreased by 30.96%.At the same time,the transcriptional levels of fatty acid desaturase genes FAD2 and FAD7 in cotyledons were obviously up-regulated during photomorphogenesis,suggesting that they may be involved in the transformation of alpha-linolenic acid and oleic acid.In the study of organelle membrane lipid compositions,compared with skotomorphogenesis,light induced a large increase of palmitoleic acid and alpha-linolenic acid in the plastid membrane,docosanoic acid,tetracosanoic acid,palmitic acid and alpha-linolenic acid in mitochondrial membrane,and palmitic acid and stearic acid in the peroxisome membrane.At the same time,the correlation analysis showed that the alpha-linolenic acid in the plastids and mitochondrias was positively correlated with the alpha-linolenic acid in cotyledons,indicating that the increase of alpha-linolenic acid in cotyledons induced by light may be closely related to the increase of alpha-linolenic acid in the plastids and mitochondrias.Unlike the cotyledons,the proportions of the three main unsaturated fatty acids including alpha-linolenic acid,linoleic acid,and oleic acid in newly differentiated tissues gradually decreased during morphogenesis,while the proportions of palmitic acid and stearic acid continued to increase.Under light conditions,the decrease of alpha-linolenic acid and the increase of palmitic acid and stearic acid were less than those under dark conditions.In addition,the accumulation of isoflavones and saponins was induced by light in the morphogenesis of A.membranaceus seedlings,and it was mainly caused by the changes of the content of formononetin and astragaloside in the newly differentiated tissues,Compared with skotomorphogenesis,H2O2 content and POD activity in cotyledons and newly differentiated tissues increased significantly during photomorphogenesis.The accumulation of secondary metabolites such as isoflavones and saponins may be involved in the redox metabolism of fatty acids in the photomorphogenesis of A.membranaceus seedlings by regulating the redox levels of histiocytes.