Multiphasic Uptake of Sulfate by Barley Roots I. Effects of Analogues, Phosphate, and pH

Abstract
For sulfate uptake by barley roots, competition studies reveal that uptake and phase transitions are caused by interaction of ions with separate sites on or in the plasmalemma. Uptake is competitively, and unequally, inhibited by sulfate analogues but not by other divalent anions. In contrast, divalent phosphate and di‐ and trivalent pyrophosphate are equally effective in causing transitions. Phosphate is taken up mainly or entirely as H2PO4 by a similar but separate multiphasic mechanism. At pH 8, sulfate uptake is mediated by fewer phases than at low and intermediate pH.