B.G. Coombe

Solute accumulation by grape pericarp cells. II: Studies with protoplasts and isolated vacuoles

Summary Protoplasts were obtained from the outer pericarp of the grape berry Vitis vinifera L. cv.“Muscat Gordo Blanco” with cellulase Onozuka R10. They agglutinated with Concanavalin A, and were intact according to the fluorescein diacetate test. Protoplasts could be lysed with DEAE-Dextran to release intact vacuoles which retained their low p H in a neutral medium. In metrizamide the vacuoles banded about ϱ = 1.094 and in Percoll about 1.079. [ 14 C]sugar uptake by protoplasts and vacuoles was diphasic. Two uptake processes, one carrier-mediated and one non-saturable, were evident in both protoplasts and isolated vacuoles. Over 1 h, uptake of L-glucose by protoplasts was only 10 % that of D-glucose at 20 mM. In protoplasts 2-deoxy-D-glucose competed with D-glucose uptake; raffinose did not compete with sucrose. Uptake from 30 mM D-[ 14 C]glucose increased 24% whilst protoplasts were incubated under pressure at 5 or 10 atmospheres. Cysteamine stimulated sucrose uptake by vacuoles. But kinetic studies of sugar uptake in isolated vacuoles gave inconsistent results with high variability.

Measurement of the changes in the composition of developing undetached grape berries by using 13C NMR techniques

Abstract A non-destructive method for detecting changes in composition during the development of unpicked grape berries has been developed. The levels of malate, tartrate, glucose and fructose have been followed by measuring the 13C NMR resonances of these constituents during berry development. The changes correlate well with known changes in berry deformability.

Solute Accumulation by Grape Pericarp Cells III. Sugar Changes in vivo and the Effect of Shading

Summary The endogenous glucose, fructose and sucrose of the skin of the grape berry has been partitioned into diffusible and residual fractions during 1G d of the phase of rapid sugar accumulation following veraison. The data have been related to total soluble solids of the perirarp juice (°Brix) as an index of development: strong correlations were found between the partitioned hexose fractions and 0 Brix, but with the notable exception of non-diffusing glucose which was most variable during this period. Sucrose did not show good correlations with other attributes. A large proportion of both glucose and fructose diffused from the skin into an osmotic buffer during 30 min of efflux: at 5 °Brix, 40—45% of each hexose diffused, and at 16 °Brix this fraction was 70 to 75%. However, the degree of eompartmentation of glucose consistently exceeded that of fructose by a small, constant amount for any given total level. A series of berries were shaded individually, a treatment known to lessen the rate of global sugar accumulation but, as shown here, having no qualitative effect upon the relationship between glucose and fructose nor upon their degrees of “compartmentation”. A tentative calculation indicates a substantial concentration gradient between the diffusible and compartmented space (compartmented space having the lower concentration) both before veraison and during rapid sugar accumulation in the tissue. Aceumulation seems essentially an increase in diffusible sugars, in whir h the primary process is probably unloading from the phloem into the apoplast rather than eventual compartmentation within the cell.