Analysis of leaf water relations in leaves of two olive (Olea europaea) cultivars differing in tolerance to salinity

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Abstract
One-year-old rooted cuttings of olive (Olea europaea L. cvs. Frantoio and Leccino) were grown either hydroponically or in soil in a greenhouse. Plants were exposed to NaCl treatments (0, 100, and 200 mM) for 35 days, followed by 30 to 34 days of relief from salt stress to determine whether previously demonstrated genotypic differences in tolerance to salinity were related to water relations parameters. Exposure to high salt concentrations resulted in reductions in predawn water potential (Ψw), osmotic potential at full turgor (ΨπFT), osmotic potential at turgor loss point (ΨπTLP), and relative water content (RWC) in both cultivars, regardless of the growth substrate. Leaf Ψw and RWC returned to values similar to those of controls by the end of the relief period. The effect of salinity on Ψπ appeared earlier in Leccino than in Frantoio. Values for ΨπFT were –2.50, –2.87, and –3.16 MPa for the 0, 100, and 200 mM salt-treated Frantoio plants, respectively, and –2.23, –2.87, and –3.37 MPa for the corresponding Leccino plants. Recovery of Ψπ was complete for plants in the 100 mM salt treatment, but not for plants in the 200 mM salt treatment, which maintained an increased pressure potential (Ψπ) compared to control plants. Net solute accumulation was higher in Leccino, the salt-sensitive cultivar, than in Frantoio. In controls of both cultivars, cations contributed 39.9 to 42.0% of the total ΨπFT, mannitol and glucose contributed 27.1 to 30.8%, and other soluble carbohydrates contributed 3.1 to 3.6%. The osmotic contribution of Na+ increased from 0.1–2.1% for non-treated plants to 8.6–15.5% and 15.6–20.0% for the 100 mM and 200 mM salt-treated plants, respectively. The mannitol contribution to ΨπFT reached a maximum of 9.1% at the end of the salinization period. We conclude that differences between the two cultivars in leaf water relations reflect differences in the exclusion capacities for Na+ and Cl− ions.

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