the presence , substrate ind cibility and regulatios ofrnthe enzyme ni trate reductase ( NADH : Nitrate Oxidored case ,rnE . C. 1.6. 6.• )(NR) of b o h ark- grown and l igh - gro n tef plantsrn( Eragr osti s te f (Zucc . ) Trotter) were st died . The relat ivernmerits of the in vivo and i n vitr o methods of assay for t hernen zyme we r e ev a l uated . Major fac ors affecting n i t r a ernr educta se act ivit y and the distr ibution of the e zyme in bothrnt h e dark- and light- grown plants wer e investigated .