Effect of the NH4/NO3 ratio on GS and PEPCase activities and on dry matter production in wheat

Previous experiments have indicated that under greenhouse and hydroponic conditions, spring wheat (Triticum aestivum L.) produces higher yields, more tillers and dry matter when supplied with mixtures of NH₄ and NO₃ than when supplied with only one of them. The goal of this study was to evaluate the effect of selected ammonium and nitrate mixtures on dry matter yield, content of soluble protein, and phosphoenolpyruvate carboxylase (PEPCase) and glutamine synthetase (GS) enzymatic activities. Cultivar ‘Salamanca’ wheat plants, 21 days old, were grown in one of five solutions containing one of the following: 7/0, 5/2, 3.5/3.5, 2/5 or 0/7 meq l^‐1 of NH₄NO₃.

After two weeks of treatment applications, the highest dry matter production in both roots and shoots of the 35‐day‐old plants was observed in plants receiving the 2/5 NH₄/NO₃ ratio. The same response was observed on the accumulation of soluble protein and the potential activity of PEPCase. The specific activity of PEPCase was related to the plant applications of ammonium.

Treatments 3.5/3.5 and 2/5 NH₄/NO₃ ratio enhanced leaf GS activity between 28 and 57 days, and it was consistently 300–500% higher than root activity during the same period. Dry weight of the leaves, stems and grain showed the highest yields with those treatments at the physiological maturity of grains (105 days).