Nitrate reductase activity and growth in Paul's Scarlet rose suspension cultures in relation to nitrogen source and molybdenum.

Growth and nitrate reductase activity were measured in Paul's Scarlet rose cell suspensions, cultured in media purified from molybdenum and containing nitrate or urea as sole nitrogen source with or without added Mo. Urea could replace nitrate to yield 80% of the fresh weight in nitrate medium. Nitrate reductase activities were compared by in vivo and in vitro assays. The latter varied due to inactivation during extraction. Compared with activities in cells in complete NO3 (-) medium, activity in NO3 (-)-Mo cells was reduced to 30% and, in urea-grown cells, to trace amounts. Increases in nitrate reductase activity were found when NO3 (-) alone was added to NO3 (-) or urea+Mo cultures. In NO3 (-)-Mo cultures, Mo alone or with NO3 (-) caused a similar increase in activity, whereas urea-Mo cultures required both NO3 (-) and Mo for enzyme induction.