Assimilation of gaseous ammonia and the transport of its products in barley and spinach leaves

Abstract

The interactions between the assimilation and transport of nitrogen and carbon were investigated in barley and spinach leaves. Both plants were fumigated with NH3 (1 mg m-3) and the content of amino acids, sucrose and carbon intermediates of amino acid metabolism were analysed in the leaves, apoplast and phloem sap. The following changes took place in the C- and N-metabolism of barley leaves during 5 h of fumigation with NH3. (a) The contents of amino acids, especially glutamine, largely increased and the contents of sucrose, 2-oxoglutarate, phosphoenolpyruvate, and glycerate-3-phosphate declined. (b) A decrease in the phosphoenolpyruvate content was accompanied by an increased activity of phoshoenolpyruvate carboxylase. (c) The altered cytosolic concentrations of amino acids and sucrose during NH3 fumigation correlated with similar changes in the apoplast and phloem sap. The altered percentage of each amino acid relative to the total amino acid concentration in the cytosol, caused by NH3 fumigation, is reflected in the apoplast and the phloem sap. The results indicate that the concentrations of amino acids in the cytosol determine their concentrations in the phloem.