Abstract
Proline transporters (ProTs) originally isolated as a highly selective transporter for proline, have been also shown to transport glycinebetaine (betaine). In this study, we examined and compared the transport properties of Bet/ProTs from betaine accumulating (sugar beet, Amaranthus and Atriplex), and non-accumulating (Arabidopsis) plants. Results revealed that all these transporters exhibited higher affinity for betaine than proline. The uptake of betaine and proline was pH dependent and inhibited by a proton uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP). These transporters exhibited a higher affinity for choline rather than betaine in the choline uptake-deficient mutant. Uptake of choline was independent of proton gradient, weakly inhibited by CCCP, and not induced by (Na+). In situ hybridization experiments showed that sugar beet BvBet/ProT1 is a salt-induced transporter mainly localized in phloem and xylem parenchyma cells. Physiological and functional properties of BvBet/ProT1 will be discussed.
