Uptake rates of (86Rb)K+ by seedling roots of six cultivars were measured and compared with K+ content of the root, K+ leakage, H+ efflux, and K+-ATPase activity of a partially purified plasmalemma fraction. Different cultivars showed significantly different rates of (86Rb)K+ uptake. The uptake rates of the first (0–5 min) period did not correlate with K+ content of the seedling roots. The rates of uptake in the 10 to 30 min period, supposed to be active, were negatively correlated with K+ content of the root. Roots consistently leaked K+ during the first 5 min. This leakage was positively correlated with the endogenous K+ content of the tissue. H+ efflux was significantly different among the cultivars and correlated with the K+-ATPase activity of a microsomal fraction partially purified on discontinuous (18/34%) sucrose gradient. The relationships among transport parameters are discussed.
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