BEHAVIOR OF PEROXIDASES IN RICE - CHANGES IN ENZYME-ACTIVITY AND ISOFORMS IN RELATION TO SALT TOLERANCE

The properties of peroxidase activities in situ and in vitro and its isoenzyme forms were compared from germinating rice (Oriza sativa) seeds and seedlings of two sets of rice cultivars differing in salt tolerance, raised under increasing levels of NaCl salinity. During 0-120 h germination period activity of peroxidase increased in endosperms/embryoaxes of all cultivars during early hours of germination with maximum at 72-96 h and decreased thereafter. In salt tolerant cvs. CSR-1 and CSR-3 salinity caused decrease in peroxidase activity in endosperms and increase in embryoaxes whereas in salt sensitive cvs. Ratna and Jaya activity increased under salinisation. During a 5-20 days growth period salinity inhibited enzyme activity in roots as well as shoots of salt tolerant cultivars whereas in sensitives it increased in seedlings under salinisation. Non salinised seedlings of sensitive cultivars maintained higher peroxidase level in roots and shoots than tolerants. Under in vitro conditions, enzyme preparations from 96 h germinated seeds or 15-day old seedlings of tolerant cvs. remained fairly tolerant to 400 mM NaCl in the reaction medium. Five peroxidase isoenzymes were detected in non salinised germinating tolerant seed parts and 4 in sensitives. Results suggest possible different behaviours of peroxidases in germinating seeds and seedlings of rice cultivars differing in salt tolerance.