Influence of NaCl Salinity on Behaviours of Nitrate Reductase and Nitrite Reductase in Rice Seedlings Differing in Salt Tolerance

Abstract

AbstractActivities of enzymes nitrate reductase (NR) and nitrite reductase (NiR) were determined in rice seedlings differing in salt tolerance raised under increasing levels of NaCl salinity. Salinity caused marked increase in in vivo NR activity in roots and shoots of salt tolerant cvs. CSR‐1 and CSR‐3 whereas in salt sensitive cvs. Ratna and Jaya a marked inhibition in in vivo NR activity was observed under salimzation. Under both controls as well as salt treatments in all cultivars roots always maintained higher level of in vivo NR activity than shoots. In vitro NR activity increased in both roots and shoots of all cultivars during early days of growth with maximum at 10–15 days and decreased thereafter. In salt tolerant cultivars salinity caused an increase in in vitro NR activity in shoots but not in roots whereas in salt sensitives activity of the enzyme was always more in salt stressed seedlings compared to controls. Salinity increased NiR activity in seedlings of sensitive cultivars whereas in tolerants suppression in root NiR activity was observed due to salinity. Like NR the activity of NiR was also higher in roots than shoots. 1 M NaCl in the enzyme assay medium suppressed in vivo NR activity in roots of 15 days old nonsalinized seedlings with more suppression in sensitive cultivars than tolerants. Results suggest possible different behaviours of nitrogen assimilatory enzymes in rice cultivars differing in salt tolerance and that salt tolerance ability is associated with high in vivo NR activity in seedlings and its further activation under salinization.