Solute Accumulation by Grape Pericarp Cells: IV. PERFUSION OF PERICARP APOPLAST VIA THE PEDICEL AND EVIDENCE FOR XYLEM MALFUNCTION IN RIPENING BERRIES

Findlay, N., Oliver, K. J., Nii, N. and Coombe, B. G. 1987.Solute accumulation by grape pericarp cells. IV. Perfusion ofpericarp apoplast via the pedicel and evidence for xylem malfunctionin ripening berries.—J. exp. Bot. 38: 668–679. ¹⁴C-labelled sucrose was applied to freshly-cut pedicels ofexcised unripe and ripening grape berries and let perfuse fordifferent periods; skin and flesh tissues were then extractedand the radioactivity partitioned and measured. Accumulationof radioactivity in a compartmented fraction was greatest inthe skin of unripe berries at the stage when sugar accumulationin vivo was slow. Total radioactivity of parts of berries showedthat activity spread rapidly throughout when the berry was unripebut slowed once ripening commenced. The perfusion of eosin from pedicels was also rapid in unripeberries but in ripe berries it was blocked beyond the pedicelat the outer edge of the 'brush' where the pericarp is aerenchymatousand tanniniferous. The failure of movement through the vascularbundles beyond the brush could not be associated with the developmentof tyloses in tracheary elements; it appeared to be associatedwith stretched tracheids in the network of dorsal vascular bundlesevidenced by irregularities in the spacing of wall thickeningsand breaks in the bounding membranes. This physical disruptionof the tracheary elements of the vascular bundles occurred whenthe berry expands suddenly, about a week after the inceptionof rapid sugar accumulation. The different rates of perfusion limit the utility of the pedicelroute for studies of compartmentation and metabolism in grapeberries at different developmental stages. Nevertheless, therapid compartmentation of radioactivity after pedicel perfusionof unripe skin with ^l4C-labelled sucrose discounts the hypothesisthat the slow rate in skin in situ is due to an apoplastic inhibitor. Key words: Grape berry, accumulation, xylem malfunction