Potassium and Sodium Absorption Kinetics in Roots of Two Tomato Species

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Abstract
Excised roots of the tomato species, Lycopersicon esculentum Mill. cv Walter (the commercial species) and of Lycopersicon cheesmanii ssp. minor (Hook.) C.H. Mull. (a wild species from the Galapagos Islands), were used in comparative studies of their absorption of K+ and Na+. Uptake of 86Rb-labeled K+ and 22Na-labeled Na+ by excised roots of ''Walter'' and L. cheesmanii varied as a function of genotype and tissue pretreatment with or without K+. Excised roots of ''Walter'' consistently absorbed more 86Rb-labeled K+ than those of L. cheesmanii. Absorption of K+ from solutions ranging from 0.01 to 0.2 millimolar KCl showed saturation kinetics in both K+-pretreated and K+ depleted roots of ''Walter'', and for K+-depleted roots of L. cheesmanii. K+-pretreated roots of L. cheesmanii had exceedingly low rates of K+ uptake with strikingly different, linear kinetics. Pretreatment with K+ caused a decrease in rates of K+ uptake in both genotypes. Potassium depleted roots of L. cheesmanii absorbed Na+ at a greater rate than those of ''Walter'', whereas K+-pretreated roots of ''Walter'' absorbed Na+ at a greater rate than those of L. cheesmanii. The results confirm and extend previous conclusions to the effect that closely related genotypes may exhibit widely different responses to the two alkali cations, K+ and Na+.