Influx of potassium (⁸⁶RB) by roots of intact tomato plants

Abstract

Seedlings of tomato (Lycopersicon esculentum Mill. cv. Matador) were grown in complete nutrient solutions at constant concentrations of potassium (K) (0.25,0.75, 1.00, 1.25, 2.20, 2.25, 3.50 mM K⁺) and three activity ratios, a_K/ (a_ca+a_Mg)> (0–007> 0–02> and 0.10 M^½). Influx of K was measured by using ⁸⁶Rb as a tracer of K. The relative growth rate of dry matter was 0.30 day¹. The content of K, calcium (Ca), and magnesium (Mg) in the plant dry matter was nearly unaffected by the concentration of K in the nutrient solution. Under these conditions it was observed that the influx of K (⁸⁶Rb) increased when the K⁺ concentration (activity) and activity ratio, a_k/ (a_Ca + a_Mg ), were increased in the nutrient solutions. Hence influx of K in tomato plants seemed to be independent of the concentration of K in the plant tissue. Possible mechanisms of the regulation of the K net uptake are discussed.