Aquaporins isoforms in cv. Touriga Nacional grapevine under water stress and recovery-Regulation of expression in leaves and roots

The aim of this work was to advance the knowledge in aquaporins expression and physiological responses of Touriga Nacional grapevine to water stress and recovery. Ungrafted grapevines cv. Touriga Nacional were subjected to two different irrigation treatments: (i) a well watered treatment (WW), in which vines were daily irrigated, being maintained at field capacity; (ii) and a water stress treatment (WS), in which vines were not irrigated along six days, with a later recovery (Rec), with these vines being re-irrigated at field capacity. Measurements started 48 h after treatments application (T1, mild stress), and from this point on, every 48 h until the maximum water stress point was reached (144 h after the beginning of the trial, T2). After this point WS plants were re-watered, and 48 h after this recovery, measurements were taken again in both treatments. The expression pattern of different aquaporins (VvPIP2;1-VvTIP1;1-VvTIP2;1-VvTIP2;2 and VvSIP) was studied in roots and leaves in both treatments at T1, T2 and Rec respectively. With the same periodicity, leaf and root specific hydraulic conductivity (Ks-leaf; Ks-root), abscisic acid (ABA) concentration, xylem sieve pH and leaf temperature were assessed. Both VvPIP2;1 and VvTIP2;2 were down regulated in WS roots, which was in line with the decrease observed in Ks-root. However, non-significant effects on Ks-leaf were observed in WS, in parallel with an up-regulation of VvPIP2;1 and VvTIP1;1. An increase of ABA in roots and leaves of WS vines was observed, in line with the results of vine water status, leaf temperature and pH of xylem sieve. Overall, results demonstrate the existence of different regulatory mechanisms occurring in response to water stress, being dependent on stress intensity and plant organ.