Sugar uptake by the grape berry: A note on the absorption pathway.

(3)H-glucose was fed to excised Sultana grape berries via their pedicels for up to 5 hours. Autoradigraphy showed that the label was distributed throughout the fruit within 1 hour. Microautoradiography of tissue sections taken at a number of points showed that within the pedicel the walls of cortical cells had become heavily labelled, suggesting that the cortical cell walls offered a diffusion pathway for the solutes entering the vascular system from the external aqueous solution. Transport along the pedicel was confined to the central vascular tissue with little radioactivity occurring in the cortical cells. Within the pericarp, the vascular bundles and walls of nearby parenchyma cells had become heavily labelled, indicating that the labelled solute was present within the vicinity of cell walls. The general pattern of (3)H-glucose accumulation by excised berries was similar to the deposition pattern of (24)C-labelled photosynthate within attached fruit.