Alkalinity induced changes in some of the enzymes of nitrogen metabolism during germination and early seedling growth of rice genotypes

Seeds of three rice (Oryza sativa L.) genotypes Viz. IR-42 (intolerant), USAR-1 and NDR-501(Tolerant) were germinated in Petri-dishes containing aqueous solution of NaHCO3 at pH of 8.5, 8.8, and 9.2 at 30+1°C in seed germinator. Seed kept for germination on distilled water served as control. Nitrate reductase (NR), Nitrite reductase (NiR) and Glutamine synthetase (GS) activities were assayed in embryonic axis after 72, 96 and 120 h, respectively after soaking. Nitrate reductase (NR) and nitrite reductase were higher in USAR-1 fallowed by NDR-501 and IR-24 respectively under normal condition. Glutamine synthetase activity on the other hand, was maximum in NDR-501 and minimum in IR-24. Activities of the entire enzyme increased with growth stage but decreased progressively with increasing level of alkalinity, though the magnitude of reduction was more in intolerant genotype IR-24. Enzymes activity in the tolerant genotype under normal as well as alkaline condition was higher and might be due to their better equipped salt tolerant mechanism. Glutamine synthetase being one of the key regulatory enzymes of nitrogen metabolism. It linked with the molecular basis of salt tolerance in rice genotypes and providing certain degree of protection against hostile environment.