Paclobutrazol as aid to reducing the effects of salt stress in Rhamnus alaternus seedlings

Rhammnus alaternus seedlings were irrigated with 0, 70 mM and 140 mM salt water in greenhouse conditions to study the effect of the drench application of 30 mg-paclobutrazol (PBZ) on the salt stress response. Overall, PBZ and salinity reduced growth and development in a cumulative way, producing plants that were too small, especially at the highest saline concentration. PBZ-treated plants showed less marginal and tip necrosis, defoliation and mortality than nontreated, especially in 140 mM-treated plants. PBZ increased the relative chlorophyll content in leaves in both saline and nonsaline conditions. Salinity significantly reduced stomatal conductance in plants not treated with PBZ. PBZ increased stomatal conductance from 37.2 to 72.3 mmol m-2 s-1 in the 70 mM-salt treatment, and from 47.8 to 68.0 in the 140 mM-salt treatment. Salinity reduced both the relative water content and water potential, but maintained turgor potential in PBZ-treated and nontreated plants as a consequence of osmotic adjustment. Although the degree of osmotic adjustment was very similar, the osmotically active compounds accumulated in each type of treatment (PBZ treated and nontreated plants) are probably different. In both saline treatments, the salt content of the leaching water increased when plants were treated with PBZ. These findings suggest that PBZ reduced saline stress symptoms and mortality in stressed plants by promoting organic solutes synthesis and by reducing the availability of saline ions in the medium (greater leaching action).