Patterns of water flow in Riesling berries in relation to developmental changes in their xylem morphology

Abstract

Using a water soluable dye as tracer, the pattern of xylem water movement within Riesling berries was found to change soon after the onset of ripening, i. e. 'veraison'. Xylem water flow appears to be both slowed and diverted. Initially it flows predominantly in the berry's peripheral xylem system but later flow is much reduced and the remaining xylem component is exclusively in the progressively less conductive axial system serving the seeds. These changes which must force proportionately more water through the phloem path appear to be brought about by morphological change - the appearance of breaks in the peripheral xylem bundles - coinciding with the period of renewed expansion growth which occurs immediately after the onset of ripening. The diversion at this stage of development of the berries water supply from the peripheral to the axial xylem, and from the xylem system to the phloem system has important implications for the fruits ultimate mineral composition.