Comparative lipid peroxidation, leaf membrane thermostability, and antioxidant system in four sugarcane genotypes differing in salt tolerance

Role of plant antioxidant systems in salt stress tolerance was studied in four contrasting sugarcane genotypes. Salt stress imposed at various stages of crop growth resulted in an increase in lipid peroxidation and decrease in membrane stability, chlorophyll fluorescence ratio (fv/fm) and chlorophyll and carotenoid contents. The activity of antioxidant enzymes (ascorbate peroixdase, glutathione reductase, and superoxide dismutase) increased significantly under salt stress. The genotypes C 92038 and Co 85004, which had the highest ascorbate peroxidase, glutathione reductase, peroxidase, catalase and SOD activity, had the lowest lipid peroxidation (malondialdehyde content) and highest membrane stability, chlorophyll and carotenoid contents under salt stress, while the susceptible genotypes Si 94050 and Co 85036 exhibited lowest antioxidant enzyme activity, membrane stability, contents of chlorophyll and carotenoid with highest lipid peroxidation. The higher salt tolerance of varieties C 92038 and Co 85004 were related to higher membrane stability, significant higher chlorophyll and carotenoid contents, and maintenance of high fv/fm ratio under salt stress and lower lipid peroxidation of membranes. Hence, the relative tolerance of a genotype to salt stress as reflected by its lower lipid peroxidation, and higher membrane stability and pigment concentration, is related to the levels of activity of its antioxidant enzymes.   Key words: Ascorbate peroxidase, carotenoid, chlorophyll, lipid peroxidation, glutathione reductase, membrane stability index, chlorophyll fluorescence ratio, sugarcane, salt stress.