Abstract
Ionic balance and N and carbohydrate metabolism studies were made on leaf and stem samples of mustard plants grown in dilute nutrient solution supplied with N as NO3 or NH4 + NOg or intermediate treatments. The inclusion of NH4- N in the nutrient medium depressed growth and decreased the concentrations of the inorganic cations (Ca, Mg, K) and the non-volatile organic acid anions, in particular malate. Irrespective of the form of N-supply, however, a fairly good balance was obtained between cation and anion equivalents in leaf and stem tissue. NH4- N in the nutrient medium increased the concentration of total N and free amino acids in the leaf tissue. In particular, there was a very high increase in the concentration of proline which appears to act as a N-reserve in white mustard. In both the stem and leaf tissue the presence of NH4- N in the nutrient medium increased the concentration of total and reducing sugars. The results are discussed with respect to the assimilation of NO, and NH4- N in relation to ionic balance and the N and carbohydrate metabolism of the plant.

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