Antioxidants and Accumulation of α-tocopherol Induce Chilling Tolerance in Medicago sativa

Chilling associated oxidative damage that enhanced the production of reactive oxygen species (ROS), slow down metabolism and modify membranes resulting in lipid peroxidation. A marked increase in the level of H2O2 was estimated in alfalfa leaves after dark chilling treatment and as a consequence, oxidation damage due to H2O2 accumulation could cause lipid peroxidation of membrane and result in a significant increase in malondialdehyde (MDA) content. After recovery period the MDA content decreased significantly due to the increase of phenolic compounds, which suppress lipid peroxidation. Also, the redox properties of α-tocopherol play an important role in adsorbing and neutralizing free radicals and provide some forms of antioxidant protection. Activity of superoxide dismutase (SOD) increased straight away the dark chilling stress, whereas catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR) activities were slightly increased after chilling treatment. During the recovery period activities of CAT, APX and GR increased significantly, which restrict the recycling of active oxygen species associated with chilling stress. The results indicated that cold treatment may have initially caused injury, thereafter during the recovery period leaves coordinated and enhanced the capacity of the antioxidative system, thus diminishing the potential for active oxygen species.