AbstractActivities of the enzymes polyphenol oxidase, indole‐3‐acetic acid (IAA) oxidase and catalase were compared from endosperms and embryoaxes of germinating rice (Oryza sativa) seeds of two sets of cultivars differing in salt tolerance, raised under increasing levels of NaCl salinity. Salt sensitive cvs.RatnaandJayawere characterized by higher polyphenol oxidase activity in embryoaxes under salinisation as compared to salt tolerant cvs.CSR‐1andCSR‐3.In endosperms of salt sensitive cultivars the enzyme activity decreased under salinisation whereas in tolerants it increased due to salinity.In vitrostudies using desalted enzyme extracts showed a continuous increase in polyphenol oxidase activity with increasing concentration of NaCl (0–1000 mM) in the reaction medium. IAA oxidase activity increased due to salinity in embryoaxes of both sets of cultivars, the effect was greater in sensitive cultivars than tolerants. NaCl when incorporated in the reaction medium caused decrease in IAA oxidase activity. Activity of catalase decreased with increase in salinity with greater decrease in sensitive cultivars than tolerants. Results suggest possible different behaviours of oxidative enzymes in germinating seeds of rice cultivars differing in salt tolerance and that salt tolerance ability is associated with lower polyphenol oxidase and IAA oxidase activities and higher catalase activity in embryoaxes under sal
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