Comparative Study On The Drought-resistant Physiology Of Four Transgenic Alfalfa

In this study,four transgenic alfalfa [transgenic alfalfa expressing cod A gene(SC),transgenic alfalfa expressing At NDPK2 gene(SN),transgenic alfalfa expressing Ib Or gene(SOR),transgenic alfalfa overexpressing At ABF3 gene(SAF)] were used as materials.They were treated with drought stress at the early flowering period through pot experiment.The drought stress was imposed by withholding the water supply to the plants.During the process that the soil water content decreased from 80%FC to 40%FC,the phenotype and physiological responses characteristics of transgenic and non-transgenic(NT)alfalfa plants and their response difference were investigated.The main results were as follows:(1)Under the sufficient water condition,the morphological characters of four transgenic alfalfa lines were different: the SC plants height were the highest and the root length were shorter;the height and root length of SN ranged in the middle,while its leaf area was the biggest among the transgenic and NT plants;the plant height and root length of SOR and SAF were significant lower than the other lines,and the leaf area of SAF was the smallest,which indicated that the expression of different resistance genes generated different effects on alfalfa phenotype.(2)When soil water content dropped to 40±5%FC,the total biomass of four transgenic alfalfa had no obvious change and SAF and SN were higher;the root/shoot ratio increased significantly(except SAF);comparing with these under 80±5%FC,the water use efficiency of transgenic lines notably increased by 85.84%-142.70%,but the total biomass of NT was significantly reduced by 47.44%,and its water use efficiency did not show obvious change,indicating that the expression of the four multi-functional improved the adaptability to drought stress by optimizing the distribution ratio of organic matter and improving water use efficiency.(3)As the soil water contents gradually decreased,the relative water content(RWC),chlorophyll content,net photosynthetic rate and Fv/Fm value exhibited decreased trends in NT and transgenic alfalfa leaves,while the accumulation of malondialdehyde and nonphotochemical quenching values showed increasing trends.When the soil water content decreased to 40±5% FC,the RWC,chlorophyll content,net photosynthetic rate and Fv/Fm value of four transgenic alfalfa leaves were significantly higher than these of NT,while thecontents of malondialdehyde and non-photochemical quenching values(except SN)were significantly lower than that of NT,which indicated that expression of multi-functional genes improved its water retention capacity,photosynthetic performance and reduced heat dissipation,meanwhile,improved the stability of membrane structure in alfalfa plants.(4)Take full consideration of the phenotype and physiological responses characteristics of each lines,we suggested that,under drought stress,SC could maintain higher photosynthetic activity and light energy conversion rate,SN exhibited strong antioxidant ability,SOR showed higher stability in photosynthesis,and SAF had higher biomass.