Varietal Differences in Rubidium Uptake Efficiency of Barley Roots

Abstract

AbstractUptake efficiency for Rb+ and SO2−4 was different in eight cultivars of barley, Hordeum vulgare L. Rb+ uptake was studied in more detail in low‐and high‐K+ plants of cv. Salve and cv. Hellas at different Rb+ concentrations in the experimental solutions.The K+/Rb+ selectivity of the roots was strongly dependent on the experimental conditions, but changed similarly in the two cultivars. After six days the fresh weight of the shoots was c. 15% higher in ‘Salve’ than in ‘Hellas’. Root development and the average concentration of K+ in the plants were the same. Influx of Rb+ in the roots was up to 75% faster in ‘Salve’ than in ‘Hellas’. Experiments with short‐term Rb+ influx (10 min) + wash (5 min) indicated that the differences in Rb+ uptake efficiency were due to variations in Rb+ influx at the plasmalemma of the root cells. Efflux of 86Rb+ from 86Rb+‐labelled roots was higher in ‘Salve’ than in ‘Hellas’ during the initial 30 min in inactive solution, indicating that passive permeation (leakage) of Rb+ and probably also of K+ at the plasmalemma of root cells of cv. Salve is faster than that of cv. Hellas. The parallel differences between influxes and effluxes explain the comparatively small difference in net uptake between the two varieties.