REPLACEMENT OF NITRATE BY AMMONIUM AS THE NITROGEN-SOURCE INCREASES THE SALT SENSITIVITY OF PEA-PLANTS .1. ION CONCENTRATIONS IN ROOTS AND LEAVES

Pea seedlings (Pisum sativum L. cv 'Kleine Rheinlanderin') were grown hydroponically in solutions containing either nitrate (3 or 14 mol m(- 3)) or ammonium (3 mol m(-3)) as the nitrogen source. Ammonium nutriti on as such had no negative effect on plant biomass production, but dra stically increased the sensitivity to moderate salinity (50 mol m(-3) NaCl). The reasons for this effect are investigated here and in a subs equent paper. The appearance of visible symptoms of salt damage (wilti ng of marginal leaf areas followed by progressive necrosis) was parall eled by the development of several characteristic modifications in the solute and metabolite contents. Major changes were: (i) high salt (Na Cl) accumulation in leaves; (ii) accumulation of ammonium (up to 20 mo l m(-3)) and amino acids (up to 110 mol m(-3)) in leaves, but at decre ased ammonium uptake rates; and (iii) decreased protein content, In a comparison paper we report on the subcellular distribution of salts, a mmonium and metabolites under the above conditions.