Abstract
Changes in the concentrations of NH(4) (+) 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 NO(3) (-) as a nitrogen source, the concentrations of NH(4) (+) 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 NH(4) (+) was added to the NO(3) (-) base starting medium, the concentration of NH(4) (+) in the cells was increased to 7.0 x 10(-1) micromoles per gram fresh weight.A comparison between the concentration of NH(4) (+) 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 NH(4) (+) 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 NH(4) (+) and amides was examined by blocking protein synthesis with cycloheximide or puromycin and measuring changes in NH(4) (+) and amide concentration over the subsequent 4 hours. The level of both NH(4) (+) 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 NO(3) (-) did not appear to be influenced by the blockage of protein synthesis.