Inhibition of Ion Uptake to Barley Roots by Cycloheximide

Cycloheximide was shown to inhibit the transport of ions into the xylem of "salt-saturated" barley roots (Hordeum vulgare cv cape), and incorporation of L-[1-14C] leucine into protein within 40—60 min. Water flow across the roots of whole seedlings was not altered for at least 180 min. Uptake of ions into the cells of "salt-saturated" roots was not affected for 120 min, but was inhibited when treated with cycloheximide for more than 120 min. H+ efflux from "low-salt" roots was inhibited by cycloheximide at about the same time as ion uptake. Measurement of ATP levels and O2uptake indicated that cycloheximide was not acting as an uncoupler of oxidative phosphorylation. The present data are considered to support the view that secretion of ions into the xylem vessels involves a specific protein with a short effective half-life, and is a separate process from active uptake into the cortical cells.