Abstract
Betaine is an important osmoprotectant in many plants, but its transport activity has only been demonstrated using a proline transporter (LeProT) from tomato, a betaine non accumulating plant. Weisolated two full length and one partial transporter genes from betaine accumulating mangrove Avicennia marinar. Their homologies to betaine transporters from bacteria and betaine/GABA transporters from mammalian cells were low, but high to proline transporters from Arabidopsis and tomato. Two full length transporters could efficiently take up betaine and proline with similar affinities and maximum velocities. The uptakes of betaine and proline were significantly inhibited by mono- and di-methylglycine, but only partially inhibited by betaine aldehyde, choline, and GABA. Sodium- and potassium-chloride markedly enhanced betaine uptake rates with optimum concentrations at 0.5 M whereas sucrose showed only modest activation.
