Major hexose transporter. Mediates an active uptake of hexoses, by sugar/hydrogen symport. Can transport glucose, 3-O-methylglucose, fructose, xylose, mannose, galactose, fucose, 2-deoxyglucose and arabinose. Confers sensitivity to galactose in seedlings. Mostly expressed in young leaves, especially in guard cells (at protein level). Also present in roots. Strong increase at the onset of the dark period followed by a progressive decrease. Transient increase at midday. Belongs to the major facilitator superfamily. Sugar transporter (TC 2.A.1.1) family.