Regulatory effects of exogenous gibberellic acid (GA3) on water relations and CO2 assimilation among grapevine (Vitis vinifera L.) cultivars

• GA3 treatment resulted in increasing cell wall elasticity in most of the cultivars.
• There is an increasing fluctuation of osmotic potential in GA3 treated grapevines.
• AWSD% was the most important parameter to indicate GA3 effect in each cultivar.
• GA3 treatment results in favourable water use efficiency in most of the cultivars.
• Magnitude of responses shows high variance to treatment in different cultivars.

Different impacts of exogenous gibberellic acid (GA3) on water relation and CO2 gas exchange in grapevine leaves were studied on four varieties belong to various ecogeographical groups. GA3 treatment resulted in increasing cell wall rigidity in some cultivars and affected the linear correlation between elasticity modulus (‘ɛ’) and relative water content at the turgor loss point (RWCTLC). The response of cultivar ‘Riesling’ agreed with the hypothesis; GA treatment resulted in increasing ‘ɛ’ values (‘ɛ’ > 12 MPa), indicating decreased cell wall elasticity. According to pressure–volume analysis, osmotic potential at full turgor (Π100) in treated ‘Sauvignon Blanc’ vines was higher compared to the controls. Results of analysis demonstrated that the four varieties showed a negative linear correlation between apoplastic water content (AWSD%) and leaf water potential at the turgor loss point (ΨTLP) and a positive linear correlation between AWSD% and RWCTLP. Values of Ci and PN showed a positive exponential correlation; Ci values increased parallel with increasing net CO2 assimilation in a range between 10 and 24 Pa of Ci both in control and treated vines. In each cultivar, intrinsic water use efficiency (WUEi) increased at reduced stomatal conductance. GA3 treatment resulted in favourable values of WUEi as expected for cultivar ‘Kadarka’ (group of convarietas pontica). WUEi was significantly (P < 0.05) lower in the GA3 treated vines compared to the controls in most of the varieties irrespective of different ecogeographical groups.