Expression,subcellular localization and phytohormone stimulation of a functional sucrose transporter (MdSUT1) in apple fruit

Sucrose transporters or carriers (SUTs or SUCs) play a crucial role in the cell-to-cell distribution of sucrose throughout the plant. Our data demonstrated that MdSUT1 is expressed almost ubiquitously in leaves, shoots, flowers and fruits, and the MdSUT1 was localized in plasma membranes of both sieve element/companion cell complex and storage parenchyma cells in apple fruits detected by immuno-gold labeling. The MdSUT1 expression was rapidly up-regulated by abscisic acid (ABA) at the translational levels in the treatments of the fruit tissues. Ten μmol L⁻¹ ABA and gibberellin acid (GA) induced MdSUT1 protein amounts dramatically, whereas 6-benzyl aminopurine (6-BA), indole-3-acetic acid (IAA) and cis-(−) ABA showed no distinct induction effect. These results suggest that MdSUT1 may be a component of ABA signaling pathways involved in the regulation of photoassimilate transport. ABA could function in plant sucrose trans-membrane transport, thus providing a clue that may help to unravel cross-talk between plant hormone and sucrose signaling pathway.