The presence, substrate inducibility and regulations ofrnthe enzyme nitrate reductase (NADH: Nitrate Oxidoreductase, . .rnE.C. 1.6.6 .â€¢ 1)(NR) of both dark-grown and light-grown tef plantsrn(Eragrostis ~ (Zucc.) 'rrotter) were studied. The relativernmerits of the in vivo and in vitro methods of assay for thernenzyme were evaluated. Major factors affecting nitraternreductase activity and the distribution of the enzyme in bothrnthe dark- and light-grown plants were investigated.rnNitrate and urea induced the formation of nitrate reductasernin 5-day-old dark-grown tef plants; and the activity of thernenzyme was predominantly associated with the roots. In thernglasshouse-grown plants, however, both the ammonia-type andrnthe nitrate-type nitrogen sources elicited NR activity althoughrnnitrate was still superior in enzyme induction; and the leavesrnwere found to be the major centeres for nitrate reduction.rnA pH of 7.6 was found to be optimal for an in vivo NRrnactiv~ty of tissue obtained from leaves of light-grown tefrnplants.rnDiurnal variations in NR activity were observed, with peakrnactivity at mid-day, suggesting that the enzyme is under therncontrol of light â€¢. Logging tef plants for 11 days after 10 days of maturationrndid not substantially affect the enzyme activity. Itrnwas observed that tef seedlings discriminate between ammoniumrnand nitrate during their early stages of development byrnpreferentially assimilating the former when given in combinationrnwith the latter. These findings suggest that tef plants can,rnat least at their early stages of development, successfullyrnwithstand reductive soil conditions.