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Ammonium Influence on the Growth and Nitrate Reductase Activity of Paul's Scarlet Rose Suspension Cultures

Department of Botany and Microbiology, The University of Oklahoma, Norman, Oklahoma 73069

Suspension cultures of Paul's Scarlet rose were grown in two defined media which differed only in their inorganic nitrogen content. Both possessed equal amounts of NO₃⁺ (24 mM), but differed in that NH₄⁺ (0.91 mM) was present in control medium; whereas, no NH₄⁺ was present in the test medium. A comparison of fresh weight increases over a 14-day growth period showed that NH₄⁺ caused a 2-fold stimulation in growth and governed the pattern of development.

Ammonium also caused a 2-fold increase in nitrate reductase activity but had little influence on the activity of representative enzymes from the Embden-Meyerhof pathway or citric acid cycle. Thus NH₄⁺ enhanced the nitrate reductase activity which was correlated with increased growth.

Ammonium had no influence on the in vitro activity of nitrate reductase which suggested that the stimulatory influence was due to an increased synthesis of the enzyme. The enhanced synthesis did not appear to be due to an increased availability of NO₃⁺ since the uptake of NO₃⁺ by intact cells was not influenced by the presence of NH₄⁺ during the period of most rapid increase in nitrate reductase activity.