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.Abbreviations FAD flavin adenine dinucleotide - Mo molybdenum - NADH reduced nicotinamide adenine dinucleotide - NO₃^-+Mo standard MX₁ culture medium - NO₃^--Mo MX₁ medium purified of Mo and used for continuous subculture with nitrate - NR nitrate reductase - PSR Paul's Scarlet rose - PVP polyvinylpyrrolidone - U urea - U+Mo MX₁ medium containing urea instead of nitrate - U-Mo MX₁ medium containing urea instead of nitrate and also purified of Mo