Mediates both low-affinity uptake and efflux of sugar across the plasma membrane. Promotes the formation of phloem bundles in mid-veins. Probably involved in the development of stomium cells that control anther opening time. Required for pollen viability (PubMed:11135107, PubMed:11405624). Forms homooligomers and/or heterooligomers. Highly expressed in nectary tissue and weakly in the stamen, especially in stomium cells and in the upper part of the filaments. Detected in the outer nectary parenchyma cells, the upper part of the filament and the anther stomium. Expressed in spots pattern on the surface of very young nectaries that do not secrete nectar and do accumulate starch. Highest levels in open flowers in which active secretion of nectar and starch hydrolysis have taken place. 'Early open anther' phenotype; anther opening in young flower buds that contain immature pollen, resulting in poor pollen quality and impaired pollen release. Belongs to the SWEET sugar transporter family.