Total peroxidase activity and peroxidase isoforms as modified by salt stress in two cultivars of fox-tail millet with differential salt tolerance

The effect of NaCl on total peroxidase activity, induction of isoperoxidase s and lipid peroxidation in 5-day-old seedlings of two contrasting genotype s of Setaria italica L. (Prasad, a salt tolerant cultivar and Lepakshi, a s alt susceptible cultivar), was studied. Total peroxidase activity increased under NaCl salinity and the degree of elevation in the activity was salt c oncentration dependent. Nevertheless, a greater activity was recorded in th e tolerant cultivar (cv Prasad) compared to the susceptible (cv Lepakshi) o ne in all days of sampling. Further, the pattern of isoperoxidases was modi fied during stress conditions as evident from the electrophoregrams. Althou gh, five acidic isoforms were detected in both cultivars, differences were found between the cultivars. Furthermore, it was observed that acidic isope roxidases were strongly expressed and an acidic isoperoxidase, A(3p) (27 kD a) is specifically found in the tolerant cultivar (cv Prasad) under NaCl st ress. This isoform was partially purified and found to be thermostable with pr 5.5 and the optimum pH 7.4. A close correlation exists between the rate of lipid peroxidation in terms of malonaldehyde (MDA) content and total pe roxidase activity per gram fresh weight with salt tolerance of the two cult ivars. The tolerant cultivar (cv Prasad) had low MDA content and high total peroxidase activity than the susceptible variety (cv Lepakshi) during sali nity stress. (C) 1999 Published by Elsevier Science Ireland Ltd. All rights reserved.