The Effect Of Low Temperature Stress On Fatty Acid Of Cell Membrane In Alfalfa Crowns

Alfalfa (Medicago sativa L.) is an important fine legume cultivated widely in the world. Cold resistance of alfalfa is the key indicator which is to be first considered while introducing and planting in North China. The structure and stability of plant cell membrane are closely related to the cold resistance of plants, which has been one of key research contents of physiological ecology of plant cold resistance. Under natural and artificial low temperature stress, by measuring the composition and content of membrane fatty acid in the rootstalk of four kinds of alfalfa with different cold resistance, the paper analyzes systematically the relationship between cold resistance of alfalfa and laws of changes as well as the validity and stability of changes of membrane fatty acid composition in the rootstalk of alfalfa in evaluation of cold tolerance of alfalfa varieties. The results show that:(1) The membrane fatty acid in the rootstalk of different varieties of alfalfa has the same composition, but there are some differences in content matching. The main components are palmitic acid (16:0), stearic acid (18:0), oleic acid (18:1), linoleic acid (18:2), linolenic acid (18:3).(2) The content of unsaturated fatty acids in the rootstalk of different varieties of alfalfa changes with temperature. The degree of unsaturated fatty acids, the ratio of unsaturated fatty acids and saturated fatty acid, the index of unsaturated fatty acid (IUFA) in the rootstalk of alfalfa were significantly negatively or very significantly negatively correlated with temperature. It confirms the fact that low temperature helps the formation of membrane of unsaturated fatty acid in the rootstalk of alfalfa.(3) Although the artificial low temperature stress can make the content of unsaturated fatty acids change, the difference among varieties was not significant, so it can not distinguish the cold resistance between alfalfa varieties.(4) In the rootstalk of alfalfa, unsaturated fatty acid content and unsaturated degree of fatty acids, unsaturated fatty acids and saturated fatty acid ratio, the difference before and after stress of IUFA values can be used as bases for evaluation of cold resistance of alfalfa.(5) According to the above indicators, the order of cold resistance in alfalfa varieties is: Zhandong alfalfa > AE702 alfalfa> WL-525HQ alfalfa, which is consistent with the results of cold resistance in field observations. It verifies the feasibility of identifying the cold resistance of alfalfa by measuring the membrane fatty acid in the rootstalk instead of the traditional field freezing observations.(6) In the rootstalk of alfalfa, palmitic acid (16:0) and linoleic acid (18:2), which are of the highest content, are highly positively related to unsaturated degree of fatty acids, and can be used as alfalfa cold indicative fatty acids.