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 NH,4 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.In previous work with suspension cultures of Paul's Scarlet rose, cells were shown to grow with only NO3+ serving as a nitrogen source, but maximum growth required a supplemental amount of either NH4+ or glutamine (22). Similar requirements were reported for suspension cultures of soybean (1, 23). Thus, in these tissue culture systems a reduced form of nitrogen such as NH4+ is required for the maximum utilization of NO3+ provided in the medium.It is well accepted that NO3+ induces the synthesis of NR1, the first enzyme in the pathway of NO3+ reduction. However, the regulatory role played by NH4+, end-product of NO3+ reduction, is less clearly understood. Ammonium has been shown to repress the induction of NR in Neurospora, Chlorella, and Lemnaceae (2). In most higher plants NH4+ either has no influence or it enhances the induction of NR by NO3-(2, 11).Based on extensive studies with genetic hybrids of corn and wheat, Hageman and colleagues (7,8)

The influence of NH4"^ on protein accumulation was examined by growing suspension cuhures of Rosa cv. Paul's Scarlet on two defined media. Both contained 1920 |xmol of NO," but only one contained 72,8 \imo\ of NH4"^. At the conclusion of a 14-day growth period, cultures grown with NH4''' possessed twice as much protein as cultures grown without NH^"^. The influence of NH4"^ did not appear to be a substrate effect, since the amount of NH4* provided accounted for only 10% of the nitrogen recovered in protein.The provision of NH4'^ in the starting medium increased the activity (nmol substrate • h"' • g~' fr wt) of glutamate dehydrogenase and glutamate synthase, and reduced the activity of glutamine synthetase. A comparison of the total activity per culture for each of these enzymes with the rate of nitrogen incorporation into protein showed that the enzymatic potential of glutamine synthetase and glutamate dehydrogenase greatly exceeded the actual in vivo rate of nitrogen assimilation through the respective pathways. Thus it was concluded that the availability of either of these enzymes does not limit nitrogen assimilation in rose cells and the fluctuations in their level brought about by NH4"*^ was of no physiological importance.The activity of glutamate synthase per culture approximated the rate of nitrogen incorporation into protein during early stages of growth, and for that reason may have limited nitrogen assimilation or caused a diversion of nitrogen through the alternative pathway to glutamate catalyzed by glutamate dehydrogenase.' Permanent address; Bibekananda Mohanty, CSRS Program,

No abstract

In this work as in previous studies from this laboratory it was demonstrated that the presence of a trace amount of NH4+ (72.8 μmol) stimulated the growth of Pauľs Scarlet Rose on a defined medium containing NO3− (1920 μmol) as the only other source of nitrogen. A kinetic analysis of several growth parameters showed that the rate of increase of dry weight, fresh weight, cell number, and cell volume were greater during early stages of growth (days 0–8) when NH4+ was provided. During later stages (days 8–14) this relationship between the two cultures did not hold. The cells provided NH4+ continued to increase in fresh weight and cell volume, but the cells which were not provided NH4+ had a greater rate of dry weight and cell number increase. These differences led to 14‐day‐old cultures which were approximately equal in dry weight and cell number but differed by a factor of 2 in fresh weight. The presence of NH4+ speeded up the development and growth of the cells.