Solute Accumulation by Grape Pericarp Cells

Abstract

Findlay, N., Oliver, K. J., Nii, N. and Coombe, B. G. 1987. Solute accumulation by grape pericarp cells. IV. Perfusion of pericarp apoplast via the pedicel and evidence for xylem malfunction in ripening berries.—J. exp. Bot. 38: 668-679. 14C-labelled sucrose was applied to freshly-cut pedicels of excised unripe and ripening grape berries and let perfuse for different periods; skin and flesh tissues were then extracted and the radioactivity partitioned and measured. Accumulation of radioactivity in a compartmented fraction was greatest in the skin of unripe berries at the stage when sugar accumulation in vivo was slow. Total radioactivity of parts of berries showed that activity spread rapidly throughout when the berry was unripe but slowed once ripening commenced. The perfusion of eosin from pedicels was also rapid in unripe berries but in ripe berries it was blocked beyond the pedicel at the outer edge of the 'brush' where the pericarp is aerenchymatous and tanniniferous. The failure of movement through the vascular bundles beyond the brush could not be associated with the development of tyloses in tracheary elements; it appeared to be associated with stretched tracheids in the network of dorsal vascular bundles evidenced by irregularities in the spacing of wall thickenings and breaks in the bounding membranes. This physical disruption of the tracheary elements of the vascular bundles occurred when the berry expands suddenly, about a week after the inception of rapid sugar accumulation. The different rates of perfusion limit the utility of the pedicel route for studies of compartmentation and metabolism in grape berries at different developmental stages. Nevertheless, the rapid compart mentation of radioactivity after pedicel perfusion of unripe skin with 14C-labelled sucrose discounts the hypothesis that the slow rate in skin in situ is due to an apoplastic inhibitor. Key words—Grape berry, accumulation, xylem malfunction. Correspondence to: Department of Plant Physiology, Waite Agricultural Research Institute, University of Adelaide, Glen Osmond, South Australia.