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Influence of Protein Synthesis on NO₃^– Reduction, NH₄⁺ Accumulation, and Amide Synthesis in Suspension Cultures of Paul's Scarlet Rose

Department of Botany and Microbiology, University of Oklahoma, Norman, Oklahoma 73019

Changes in the concentrations of NH₄⁺ and amides during the growth of suspension cultures of rose (Rosa cv. Paul's Scarlet) cells were examined. When cells were grown in medium possessing only NO₃^– as a nitrogen source, the concentrations of NH₄⁺ and amides increased to 4.0 x 10^–1 and 5.9 micromoles per gram fresh weight, respectively. The amounts of both constituents declined during the later stages of growth. When a trace amount of NH₄⁺ was added to the NO₃^– base starting medium, the concentration of NH₄⁺ in the cells was increased to 7.0 x 10^–1 micromoles per gram fresh weight.

A comparison between the concentration of NH₄⁺ in the cells (4.3 x 10^–4 molar) with the K_m values for glutamate dehydrogenase (5 x 10^–3 molar) and glutamine synthetase (1.7 x 10^–5 molar) showed that the endogenous NH₄⁺ would have to be concentrated 10-fold in compartments possessing glutamate dehydrogenase in order for the substrate to reach one-half the saturation level for that enzyme.

The influence of protein synthesis on the level of NH₄⁺ and amides was examined by blocking protein synthesis with cycloheximide or puromycin and measuring changes in NH₄⁺ and amide concentration over the subsequent 4 hours. The level of both NH₄⁺ and amides showed substantial increases when protein synthesis was blocked. Ammonium accumulated to concentrations surpassing those reported by other authors to be toxic to plants. The reduction of NO₃^– did not appear to be influenced by the blockage of protein synthesis.