Nitrogen metabolism in the leaves of Pennisetum glaucum (L) as affected by water stress

Activities of nitrate reductase (NR, both in vitro and in vivo), nitrite reductase (NiR), glutamine synthetase (GS1 and GS2) and glutamate dehydrogenase (GDH) in the leaves of Pennisetum glaucum (Bajra) declined following water stress imposed by withholding irrigation for different duration (24–60 h). Both the catalytic activities of nitrate reductase, viz. terminal nitrate reductase and NADH-nitrate reductase (total NR activity) got impeded in water stressed seedlings. Though the enzymes of ammonia assimilation were also affected by water withholding, but the level of reduction was less than that of nitrate assimilation. The isoforms of GS were differently affected by drought stress. GS1 activity declined more (54–63%) as compared to GS2 (21–31%) at 36 and 48 h of water withholding. The enzyme activities were recovered upon supply of water to 36 h-stressed plants. However, the plants subjected to longer period of water withholding (48 and 60 h) could show only the partial recovery of enzymes upon rewatering. The fast response of enzymes to change in water status of the plants could be due to post-transcriptional modification or inactivation of the enzyme(s).