Nitrate assimilation in suspension cultures of Paul's scarlet rose

Abstract

Nitrate reductase activity, the assimilation of NO3−, and growth were studied in suspension cultures of Rosa cv. Paul's Scarlet grown in media with either 24 mM NO3−,or with 24 mM NO3− + 0.91 mM NH4+.Ammonium partially repressed the development of nitrate reductase during the first 4 days of growth and the degree of repression was more pronounced when cells were provided with lower concentrations of NO3−. The repression of nitrate reductase by NH4+ was only observed when casein was used during enzyme extraction. The repression of nitrate reductase activity by NH4+ was not recognized in earlier work when no casein was used.The presence of casein in the extraction or assay medium increased the total recoverable nitrate reductase activity. The enhancement was differential depending on cell age with the greatest influence being on young and old cells where 100 and 400% enhancements were observed, respectively.In vitro nitrate reductase activity correlated well with NO3− assimilation. Over 14 days of growth, the ratio of total nitrate reductase activity to the total amount of NO3− reduced was 3.8 for cultures grown with or without NH4+. Cultures grown with NH4+ achieved 80% more fresh weight and reduced 70% more NO3− over 14 days than cultures grown without NH4+.