De Novo Synthesis of Plasma Membrane and Tonoplast Polypeptides of Barley Roots during Short-Term K Deprivation : In Search of the High-Affinity K Transport System

Abstract

[(35)S]Methionine labeling of intact barley roots (Hordeum vulgare cv Klondike) after short (6-12 h) and longer (18-24 and 90-96 h) periods of K(+) deprivation revealed that several membrane polypeptides were synthesized in significantly increased amounts following withdrawal of K(+) from nutrient solutions. One of these, a 43-kD polypeptide localized in plasma membrane- and tonoplast-enriched fractions, accounted for a large part of (35)S incorporation into membranes when [(35)S]methionine was administered for 6 h following 6 h of K(+) deprivation. With increasing duration of K(+) deprivation, (35)S incorporation into this 43-kD polypeptide decreased. This polypeptide, referred to as KR43, was not synthesized when NO(3) (-) or inorganic phosphate was removed or when Rb(+) was substituted for K(+). However, it was synthesized when K(+) was removed and replaced by an equivalent concentration of Na(+). The intrinsic nature of this polypeptide and the time course of changes in its expression, which correspond with changes of K(+)((86)Rb) influx associated with K(+) deprivation, provide evidence that this polypeptide may form part of the high-affinity K(+) transport system in barley roots. A possible role for this polypeptide is discussed in the context of changes in the subcellular distribution of K(+) in barley roots following interruption of K(+) supply. A 45-kD microsomal polypeptide, identified in earlier studies as a response to K(+) deprivation, is suggested to be an extrinsic protein, readily displaced from membranes by exposure to ethylenediaminetetraacetate.