GROWTH AND NUTRIENT-UPTAKE BY BARLEY (HORDEUM-VULGARE L CV HERTA) - STUDIES USING AN N-(2-HYDROXYETHYL)ETHYLENEDINITRILOTRIACETIC ACID BUFFERED NUTRIENT SOLUTION TECHNIQUE .2. ROLE OF ZINC IN THE UPTAKE AND ROOT LEAKAGE OF MINERAL NUTRIENTS

Barley seedlings (Hordeum vulgare L. cv Herta) were grown in N-(2-hydroxyethyl)ethylenedinitrilotriacetic acid-buffered nutrient solutions with or without adequate Zn supplies. Fifteen-d-old Zn-deficient seedlings contained higher concentrations of Mn, Ca, Mg, and P in their shoots and more fe, Mn, Cu, K, Ca, and P in their roots than did similar Zn-adequate seedlings, confirming results reported in our companion study (W.A. Norvell and R.M. Welch [1993] Plant Physiol 101: 619-625). Zn-deficient roots leaked greater quantities of K, Mn, Cu, and Cl than did roots supplied adequately with Zn; they also leaked significant amounts of Zn even though the seedlings were not supplied Zn during growth. Calculated uptake rates of P, Mn, and Na were sharply reduced, but uptake rates of K and Mg were stimulated by increasing the Zn2+ activity in nutrient solutions. Intact roots of Zn-deficient seedlings contained lower concentrations of 5,5'-dithio-bis(2-nitrobenzoic acid) reactive sulfhydryl groups in comparison to Zn-adequate roots. Apparently, Zn is required for the uptake and retention of several mineral nutrients by roots, possibly by playing a protective role in preventing the oxidation of sulfhydryl groups to disulfides in root-cell plasma membrane proteins involved in ion channel-gating phenomena.