Differential physiological and biochemical responses to drought in grapevines subjected to partial root drying and deficit irrigation

• The irrigation amount applied differentiates the effects of PRD and DI in vines.
• Cytokinins play the preponderant role in mediating stomatal behavior in PRD.
• ABA concentration dominates stomatal responses in DI grapevines.
• DI induced a more pronounced decrease in plant's growth.

The effects of two different irrigation methodologies, partial root drying (PRD) and deficit irrigation (DI), on grapevines (Vitis vinifera L., cv. Mavrodafni) physiological and biochemical parameters were studied using split-rooted potted plants. Five irrigation treatments were applied: fully irrigated (FI) at both parts of the rootzone to soil capacity; deficit irrigated (DI50 and DI25) receiving 50% and 25% irrigation water of FI plants, respectively, to the entire rootzone and partial root drying (PRD50 and PRD25) receiving 50% and 25% irrigation water of FI plants, respectively, which was successively applied to one and the other part of the rootzone. Compared with DI50, PRD50 plants exhibited higher stomatal conductance and photosynthetic rate maintaining more favorable plant water status throughout the experimental period. On the contrary, no significant differences in physiological parameters between PRD25 and DI25 plants were observed, suggesting that irrigation amount could influence different irrigation methodologies effects on plant's performance. Leaf abscisic acid (ABA) concentration at the end of the drought period was significantly higher in DI compared to PRD plants while the opposite trend was evident concerning cytokinins (Cks) concentration. Irrespective the irrigation amount applied, stomatal conductance (gs) in DI plants exhibited the strongest correlation with leaf abscisic acid (ABA) concentration among the treatments but this relationship was significantly weakened when gs was regressed against ABA/CKs ratio. PRD plant's stomatal conductance was also strongly correlated with leaf abscisic acid (ABA) concentration but this relationship was markedly improved when ABA/CKs ratio was used. These results imply a more pronounced role of CKs in mediating stomatal responses in PRD plants. In contrast in DI grapevines ABA concentration seemed to dominate stomatal responses to drought.