Physiological and biological responses of alfalfa shoots and roots to salt stress

Abstract

The study was carried out to reveal the changes of growth and antioxidant system in different organs of alfalfa seedling under salt stress and to provide some support for the study on alfalfa vegetation resumption. Two alfalfa cultivars, Xinmu No.1 (tolerant cultivar) and Northstar (sensitive cultivar) were used as the plant materials, and 0, 200 mmol/L NaCl was used as control and stress treatment respectively. The study analyzed the seedling growth, H2O2 contents, MDA contents, membrane damage, activity and isozymes of antioxidant enzymes of alfalfa shoots and roots treated 7 days by 200 mmol/L NaCl. NaCl stress inhibited the growth of alfalfa shoots and roots, and resulted in the increase of H2O2, MDA contents and membrane damage. Lower degree of growth restraint effect and membrane damage of shoot and root organs were exhibited in Xinmu No.1 than Northstar. Under salt stress, antioxidant enzyme activity including superoxide dismutase (SOD), ascorbate peroxidase(APX), catalase (CAT) and peroxidase (POD) significantly increased. The capability of scavenging reactive oxygen species (ROS) took on organ difference in CAT and POD. The CAT activity in shoot was higher than that in root, but reversed in POD. SOD-Ⅱ, APX-Ⅰ, POD-Ⅲ and POD-Ⅳ were identified as sensitive isozyme bands to salt stress. Tolerant alfalfa cultivar can reduce the damage by enhanced antioxidant protective ability under salt stress.