Grape vine varieties Shiraz and Grenache differ in their stomatal response to VPD: apparent links with ABA physiology and gene expression in leaf tissue

Two cultivars of Vitis vinifera L., namely Grenache and Shiraz, have been described as having near-isohydric and near-anisohydric responses respectively to soil water stress (Schultz, Plant Cell and Environment, 26, 1393-1405, 2003). Given that contrast in sensitivity to soil water, a question arises as to whether atmospheric moisture stress will elicit similar differences. The present Study was undertaken to investigate this issue by comparing stomatal responses in these same two cultivars to contrasting vapour pressure deficit (VPD). Test material included field grape vines in the Barossa Valley and pot-grown vines under partial shade in Adelaide. Our experiments showed that the same isohydric/anisohydric distinction as described by Schultz (2003) is apparent in leaf responses to atmospheric moisture stress. in the more isohydric cultivar, Grenache, stomatal conductance is more responsive to changes in VPD. This heightened sensitivity (compared with Shiraz) appears to be associated with higher levels of abscisic acid (ABA) in Grenache xylem sap. Expression studies on the key genes in the ABA biosynthetic pathway indicate that regulation of the Vv.ncedl gene expression in leaf tissue, but not in the root tissues, is associated with the changes in the xylem sap ABA. Moreover, the two cultivars (Grenache and Shiraz) differed with respect to both scale and time course of those responses. We conclude that these two Vitis vinifera cultivars do indeed differ significantly in the way that they respond to potentially stressful atmospheric conditions, and that ABA physiology is a key process in these contrasting responses. An understanding of such mechanisms, including the relative importance of roots and shoots in determining vine response to abiotic stress, is highly relevant to irrigation scheduling, and to management of associated variation in vineyard productivity across diverse environments.