Ammonia metabolism in the leaves and ears of wheat (Triticum aestivum L.) during growth and development

Abstract

The pattern of free NH₄⁺ accumulation and its metabolism was studied during the growth and development of field-grown wheat cv. HD 2204 at two applied N levels viz. 30 and 120 kg ha^-1. The study was confined to the 3rd, 5th and flag leaf blades and the developing ears, borne on the main shoot, during their ontogeny. The NH₄⁺ levels were considerably lower in young leaves and increased sharply as the leaves senesced when the activity of glutamine synthetase (GS) declined. In contrast to GS, glutamate dehydrogenase (GDH) remained active even during senescence. Concentrations of protein, free amino acid and total reduced N declined with age in the leaves. An assessment of free NH₄⁺ pool, free amino acid content and the activity of GS and GDH in the floral parts revealed that glumes, awns and grains also were active sites of NH₄⁺ turnover. Higher applied N level not only increased leaf and grain N concentration but also led to higher free NH₄⁺ levels in leaves and in developing ears. Presence of NH₄⁺ in the entrapped transpirate revealed that NH₄⁺ is released from both leaves and ears during senescence.