Influx of potassium (Rb-86) by roots of intact tomato plants

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-1/2). Influx of K was measure d by using Rb-86 as a tracer of K. The relative growth rate of dry matter w as 0.30 day(-1). The content of K, calcium (Ca), and magnesium (Mg) in the plant dry matter was nearly unaffected by the concentration of K in the nut rient solution. Under these conditions it was observed that the influx of K (Rb-86) 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 i n the plant tissue. Possible mechanisms of the regulation of the K net upta ke are discussed.