| Alfalfa(Medicago sativa L.)is one of the most cultivated perennial legumes in the world,known as the king of forages.However,extreme environmental conditions,such as low temperature,salinity and drought,are the main factors affecting the growth and nutritional quality of alfalfa.In this paper,three varieties of alfalfa(Tumu No.2,Aohan and Zhongmu No.1)were selected as the research objects to compare their response mechanisms to salt,drought and low temperature stresses and the effects of various stresses on their feeding quality;Based on fluorescence quantitative RT-PCR and RNA sequencing,the response mechanism of three alfalfa varieties to low temperature stress was further studied.The main results are as follows:1.Under salt stress,the growth status of Aohan were better than the other two varieties of alfalfa,which indicated that the salt tolerance of Aohan was stronger than Tumu No.2 and Zhongmu No.1;The contents of chlorophyll,MDA,superoxide anion,proline and the activities of several antioxidant enzymes of three varieties of alfalfa showed different trends,which suggested that there were some differences in the response mechanism of three varieties of alfalfa to salt stress;Under salt stress,the content of crude fiber in three varieties of alfalfa decreased,but the content of crude ash,neutral detergent fiber and acid detergent fiber did not change significantly.2.Under drought stress,Zhongmu No.1 had the least effect on growth status,which indicated that Zhongmu No.1 had stronger drought tolerance than Aohan and Tumu No.2;Under drought stress,the chlorophyll content of three varieties of alfalfa decreased,MDA,superoxide anion,proline content and several antioxidant enzyme activities increased in varying degrees,which suggested that the drought tolerance mechanism of three varieties of alfalfa was different;Under drought stress,the content of crude ash decreased,while the content of crude fiber,neutral detergent fiber and acid detergent fiber increased slightly.3.Under low temperature stress,Tumu No.2 had the lowest effect on growth status,which indicated that Tumu No.2 had stronger cold tolerance than Zhongmu No.1 and Aohan;Under low temperature stress,the content of chlorophyll decreased,and the content of MDA,superoxide anion,proline and the activities of several antioxidant enzymes increased in different degrees,which suggested that there were some differences in the cold tolerance mechanism of the three alfalfa varieties;Under low temperature stress,the contents of crude ash,crude fiber,neutral detergent fiber and acid detergent fiber in three kinds of alfalfa were inhibited,but the influence of crude ash was less;Twelve genes related to low temperature stress were up-regulated in different degrees in three varieties of alfalfa under low temperature stress.4.Transcriptome sequencing results showed that the three alfalfa varieties responded to low temperature stress mainly through photosynthesis,respiratory metabolism,fatty acid degradation and unsaturated fatty acid synthesis,sugar metabolism,amino acid metabolism,secondary metabolite synthesis,increase of antioxidant protectors,phosphatidylinositol signaling pathway,DNA repair and other ways. |
