EVIDENCE FOR XYLEM DISCONTINUITY IN PINOT-NOIR AND MERLOT GRAPES - DYE UPTAKE AND MINERAL-COMPOSITION DURING BERRY MATURATION

To estimate changes in xylem flow during greenhouse- and field-grown g rape (Vitis vinifera L.) berry maturation, apoplastic dye (aqueous Eos in Y or azosulfamide) was allowed to suffuse through cut pedicel ends. Dye uptake in colored Pinot noir berries was significantly less than that in pre-colored berries. Dye distribution in soft-green berries wa s uneven in comparison to that in firm-green berries, suggesting that xylem discontinuities occur as the berries soften. Merlot clusters, co llected from the field near veraison and the berries separated by defo rmability and color, showed distinct differences in dye uptake and dis tribution in soft-green versus firm-green berries. Pinot noir and Merl ot berry deformability increased sharply before berry coloring (approx imately 3 days before for Pinot noir), and in some cases preceded the second rapid berry expansion. In Pinot noir, total K+ per berry increa sed rapidly after veraison, but total Ca2+ per berry did not. Dye upta ke and Ca2+ accumulation patterns suggested increased flow resistance in the xylem after veraison. Berry softening coincided with a change i n dye uptake patterns and sometimes occurred before the resumption of rapid berry growth.