Genotypic difference in response of peroxidase and superoxide dismutase isozymes and activities to salt stress in barley

Difference in isozymes and activities of peroxidase (POD) and superoxide dismutase (SOD) in two barley (Hordeum vulgare L.) genotypes differing in salt tolerance (Gebeina, tolerant; Quzhou, sensitive) was investigated using a hydroponic experiment. The activities of both enzymes were significantly increased when the plants of the two barley genotypes were exposed to salt stress, with salt-tolerant genotype being generally higher than the sensitive one. The variation in the POD and SOD isozymes was dependent on barley genotype, salt level and exposure time. When the plants were exposed to salt stress for 10 days, two new POD isozymes were found, R _m0.26 (R _m, relative mobility of enzyme to dye) in Gebeina and R _m0.45 in Quzhou. Both isozymes disappeared after 20 days of salt stress, but R _m0.26 appeared again 30 days after the stress. Two new SOD isozymes of R _m0.19 and R _m0.46 were found in Gebeina when exposed to NaCl for 10 days, but only R _m0.46 in Quzhou. As the time of salt stress extended, more new SOD isozymes were detected, R _m0.35 in both genotypes in all different salt treatments and R _m0.48 in Gebeina under 200 mM NaCl stress. At 30 days after the stress, all the new SOD isozymes disappeared except for R _m0.48 in Gebeina under 200 mM NaCl stress. The results suggest that the increased POD and SOD activities could be partly due to the formation of some new isozymes and the tolerant variety had better ability to form new isozymes to overcome salt stress.