Chapter 6. Embolism formation and removal in grapevines: a phenomenon affecting hydraulics and transpiration upon water stress.

Drought signalling among grapevine organs has a dual component: a hydraulic signal controlled by xylem physiology coexists with chemical signals (involving hormones, especially abscisic acid, ABA), transported via xylem, phloem and parenchyma pathways. Under water deficits, with high levels of tension developing, gas-filled xylem vessels may become disrupted by breakage of water columns, producing the so-called cavitation (or embolism) that drastically reduces hydraulic conductance. In grapevine, petioles and roots have been shown to be more vulnerable to xylem cavitation than shoots. When grapevines are re-watered following a drought period, either root or shoot and petioles recover 35–40% of hydraulic conductivity within 24 h, suggesting that a common and coordinated mechanism of recovery among plant organs occurs. To reintegrate vessel functionality, plants have developed different repair mechanisms, which involve active and energy-consuming processes in shoot conductive tissues, possibly involving the contribution of aquaporins. The role of ABA in xylem embolism repair during diurnal cycles is also apparent and discussed.