Leaf gas exchange and abscisic acid in leaves of Glera grape variety during drought and recovery

"Grapevine performance under drought largely depends on the varietal physiological and hydraulic strategies adopted in response to water stress. In this study we aimed to characterize the main ecophysiological traits of 'Glera' wine grape variety, for which no studies on water relations and ABA dynamics have so far been reported. Potted 'Glera' plants were subjected to prolonged mild and severe water stress conditions and compared with control plants. The course of leaf gas exchange, stem water potential (Wstem) and leaf ABA concentration were followed during the stress imposition and the rehydration processes. Yield and quality parameters were also measured at harvest. 'Glera' subjected to both severe and mild stress showed decreased leaf gas exchange, Wstem, agronomic and quality parameters. This was particularly evident in the severe stress, where net photosynthesis decreased progressively to zero due to significant stomatal limitation and it did not fully recover after rehydration. Agronomic and berry quality features measured at harvest did not recover either. In both stress treatments leaf ABA concentration increased only after stomatal closure and, for severe drought, ABA remained at high concentration till one day after re-watering. Re-watered plants quickly recovered Wstem while stomatal conductance gradually increased only when leaf ABA concentration decreased. In the present study, stomatal limitation was hydraulic dependent, while the decrease in leaf ABA concentration following re-watering was associated with gradual recovery of leaf gas exchange"