UPTAKE AND ASSIMILATION OF AMMONIUM-IONS BY CUCUMBER SEEDLINGS FROM SOLUTIONS WITH DIFFERENT PH AND ADDITION OF HEAVY-METALS

Influence of Cu2+, Cd2+, Pb2+ and Fe2+ in various pH conditions (5.0, 6.0, 7.0) on the uptake and assimilation of NH4+ by cucumber seedlings was estimated. Every metal in different pH of uptake solution distinc tly reduced ammonium absorption calculated from NH4+ depletion. Copper and ferric ions, but not cadmium or lead, astonishingly decreased the uptake of ammonium from solution at pH 5.0. Cu2+ was also very active at pH 6.0. The accumulation of ammonium in roots of metals-treated se edlings at the same time was high. The high level of ammonium in root cells despite of its low uptake probably resulted from disturbance in NH4+ assimilation. Both glutamine synthetase (GS) and NADH-glutamate d ehydrogenase (NADH-GDH) - the major enzymes in ammonium assimilation, were inhibited after one hour of plant exposition to the metals. Simil arly as in the case of ammonium uptake, the influence of pH was visibl e only in combination with copper and ferric ions. The strongest reduc tion of enzyme activities was observed for Cu2+ and Fe2+ in pH 5.0 and 6.0. The various metals absorption by roots from solutions with diffe rent pH was not dedected. The data show correlation between metal inhi bition of GS and NADH-GDH activities and metal inhibition of ammonium absorption.