GROWTH, ION DISTRIBUTION, POTASSIUM AND NITRATE UPTAKE OF LEUCAENA-LEUCOCEPHALA, AND EFFECTS OF NACL

Three to six-week old plants of Leucaena leucocephala (Lam.) de Wit, c v K8, were grown hydroponically without root nodules. They showed much better growth response to nitrate than to ammonium. They were found t o be tolerant to salinity of up to 50 mM NaCl. Effects of salinity in this range and moderate Na+ accumulation in young organs could be alle viated by supplying 10 mM nitrate to the medium. Na+ mainly accumulate d in basal leaves and cotyledons as disposable organs. Distribution of Cl- was more uniform than of Na+, its exclusion from young organs by nitrate was less effective. K+ distribution in the plants was almost u niform and little affected by NaCl, while nitrate accumulated only in the roots and at high external concentrations. Nitrate uptake of N-sta rved plants initially showed higher rates, a minimum after 2 h and the n increased during several hours suggesting a constitutive and an indu cible transport component. Induction of nitrate assimilation was shown by nitrate reductase activity (EC 1.6.6.2). Nitrate uptake was not af fected by 20 mM NaCl. In K+- and N-starved plants uptake rates of K+ r oughly followed those of nitrate. In N-supplied plants nitrate reducta se activity was found mainly in the roots, where in starved plants ind uction was also strongest. In the nutrient supplied culture salt treat ment especially stimulated nitrate reductase activity in the roots. In general, counteraction of nitrate to salinity effects occurs in distr ibution of the ions within the plant but only at low salinity.