Hydric Behavior: Insights into Primary Metabolites in Leaves and Roots of Cabernet Sauvignon and Grenache Grapevine Varieties under Drought Stress

The classification of grapevine cultivars into isohydric and anisohydric categories depends on their ability to close stomata under conditions of low soil water availability or high atmospheric demand. This study aimed to compare the responses of Grenache, classified as isohydric, and Cabernet Sauvignon, classified as anisohydric, both grafted onto Richter 110 rootstock, and subjected to severe drought stress. Three cycles of drought stress were applied, followed by watering, while a well-watered treatment served as the control. Stomatal conductance and stem water potential were measured at predawn and midday during the drought cycles, and primary metabolites were analyzed in leaves and roots using gas chromatography. We found that Grenache had significantly higher stomatal conductance than Cabernet Sauvignon under both well-watered and water-stressed conditions. There were no significant differences in stem water potential between the two varieties, but the control treatment maintained a higher stem water potential at predawn and midday for both varieties. Primary metabolite analysis showed that both varieties accumulated sugars and polyols in their leaves and roots under drought stress, while organic acids were more abundant in leaves than in roots. Overall, the results suggest that the hydric behavior of grapevines depends on the intensity and duration of drought stress. In this study, both varieties exhibited near-isohydric behavior by regulating stomatal closure under drought stress. The metabolites identified in this study may serve as potential biomarkers of water drought stress in Grenache and Cabernet Sauvignon grapevines under the conditions of this experiment.