The Influence of Initial Salt Status on Absorption of Rubidium by Corn Root Segments of Two Stages of Development

Abstract

VENRICK, DANA M., and RICHARD C. SMITH. (Univ. of Florida, Gainesville.) The influence of initial salt status on absorption of rubidium by corn root segments of two stages of development. Bull. Torrey Bot. Club 94: 501-510. 1967.-Apical and basal root segments (consisting primarily of meristematic and elongated cells, respectively) of 4-day corn seedlings were tested for various characteristics of active transport, both with and without a preliminary exposure to KCl for 24 hours. The tissue was permitted to absorb Rb+ from a 0.1 mM RbCl solution labelled with 86Rb. Labelled ions held by adsorption or present in the apparent free space were removed prior to radioactive assay. The results show that both apical and basal segments displayed the following characteristics of active transport: absorption resulted in high accumulation ratios; the absorbed ions were retained by the tissue in the presence of external KCl solution; K+ in the experimental solution inhibited uptake whereas Na+ did not; lowering the temperature reduced the rate of uptake to such an extent that Q1o values were greater than 2.0. Pretreatment of the seedlings for 24 hours with 1.0 mM KCI resulted in a subsequent reduction in rate of Rb+ absorption by apical segments but had little effect on absorption by basal segments. In both kinds of segments pretreatment with KCI was followed by the same characteristics of active transport of Rb+ described above. These data provide support for the existence of active transport of Rb+ into both apical and basal corn root segments, and they also show that a long exposure to KCl does not prevent subsequelnt active transport of Rb+.