Water relations and osmotic adjustment in Lycopersicon esculentum and L. pennellii during short-term salt exposure and recovery

Cultivated tomato Lycopersicon esculentum (L.) Mill. cv. P-73 and its wild salt-tolerant relative L. pennellii (Correll) D'Arcy accession PE-47 growing on silica sand in a growth chamber were exposed to 0, 70, 140 and 210 m M NaCl nutrient solutions 35 days after sowing. The saline treatments were imposed for 4 days, after which the plants were rinsed with distilled water. Salinity in L. esculentum reduced leaf area and leaf and shoot dry weights. The reductions were more pronounced when sodium chloride was removed from the root medium. Reduction in leaf area and weight in L. pennellii was only observed after the recovery period. In both genotypes salinity induced a progressive reduction in leaf water potential and leaf conductance. During the recovery period leaf water potential (ψ₁) and leaf conductance (g₁) reached levels similar to those of control plants in wild and cultivated species, respectively. Leaf osmotic potential at full turgor (ψ_os) decreased in the salt treated plants of both genotypes, whereas the bulk modulus of elasticity was not affected by salinity. Leaf water potential at turgor loss point (ψ_tlp) and relative water content at turgor loss point (RWC_tlp) appeared to be controlled by leaf osmotic potential at full turgor (ψ_os) and by bulk modulus of elasticity, respectively. At lowest salinity, the wild species carried out the osmotic adjustment based almost exclusively on Cl⁻ and Na⁺, with a marked energy savings. Under highest salinity, this species accommodate the stress through a higher expenditure of energy due to the contribution of organic solutes to the osmotic adjustment. The domesticated species carried out the osmotic adjustment based always on an important contribution of organic solutes.