ASSIMILATION OF GASEOUS AMMONIA AND THE TRANSPORT OF ITS PRODUCTS IN BARLEY AND SPINACH LEAVES

The interactions between the assimilation and transport of nitrogen an d carbon were investigated in barley and spinach leaves. Both plants w ere fumigated with NH3 (1 mg m(-3)) and the content of amino acids, su crose and carbon intermediates of amino acid metabolism were analysed in the leaves, apoplast and phloem sap. The following changes took pla ce in the C-and N-metabolism of barley leaves during 5 h of fumigation with NH3. (a) The contents of amino acids, especially glutamine, larg ely increased and the contents of sucrose, P-oxoglutarate, phosphoenol pyruvate, and glycerate-3-phosphate declined, (b) A decrease in the ph ophoenolpyruvate content was accompanied by an increased activity of p hosphoenolpyruvate carboxylase, (c) The altered cytosolic concentratio ns of amino acids and sucrose during NH3 fumigation correlated with si milar changes in the apoplast and phloem sap. The altered percentage o f each amino acid relative to the total amino acid concentration in th e 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.