Contrasting responses of two grapevine cultivar with different hydraulic behaviour to drought: the role of non-structural carbohydrates in xylem embolism

Xylem embolism is one of the effects triggered by the increase in xylem tension when plants face drought. Some species have been shown to recover from embolism and recent studies have highlighted the role of non-structural carbohydrates (NSC) in the generation of osmotic gradients required for the refilling of the embolized vessels. In the frame of the classification of plants according to their isohydric/anisohydric strategies, this study aims to evaluate embolism recovery in two grapevine cultivars considered at the opposite edges of the isohydric/anisohydric continuum. In particular, the connection with non-structural carbohydrates (NSC) was investigated. One-year grafted plants of Grenache (isohydric) and Barbera (anisohydric) were subjected to an intense water stress followed by a resumption of irrigation. The degree of embolism and its recovery at the stem level were quantified in vivo by micro-CT analysis and followed by xylem anatomical evaluation and NSC analysis. Both cultivars recovered the embolism after a resumption of irrigation even if Barbera plants were constitutively more prone to embolism. Modulation of soluble carbohydrates pattern during water stress and recovery at the expenses of starch was observed in both cultivars. However, only in Grenache plants a direct relationship between the soluble carbohydrate content and the degree of embolism was observed, evidencing its direct involvement in the embolism recovery process. Our findings showed that the two cultivars used different strategies in response to drought, suggesting an NSC-mediated recovery only for the isohydric Grenache.