Abstract :
The study was carried out under greenhouse conditions in two experiments: first experiment was designed to compare the effects of iso-osmotic treatments (150 mM NaCl and 20% PEG-6000 solutions) on stomatal conductance, leaf water potential and leaf relative water content in pistachio seedlings. Three-month-old seedlings of Pistacia atlantica subsp. mutica, Pistacia vera “Sarakhs”, and Pistacia vera “Badami” were exposed to different treatments. The experiment was a factorial combination of three seedling rootstocks and three treatments, each replicated three times, and arranged in a randomized complete block design. Sampling for relative water content, water potential and stomatal conductance were carried out on 1st, 7th, and 14th days after application of treatments. In the second experiment, 36-month-old seedlings of the three rootstocks of pistachio were used. They were irrigated daily with two levels of salt solution (0 and 150 mM NaCl) imposed by the stepwise method. The experiment was a factorial combination of three seedling rootstocks and two treatments, each replicated five times, and arranged in a randomized complete block design. Harvesting was carried out on the 10th day after salinization for measurement of ABA in xylem sap. Stomatal conductance in the controls showed little change throughout the experiment, although there were consistent cultivar differences, with P. atlantica subsp. mutica having the highest and P. vera “Badami” having the lowest values throughout. In the stress treatments, stomatal conductances decreased gradually over time with the NaCl treatment showing more powerful effects than the PEG treatment. The leaf water potential and leaf water content of salt and polyethylene glycol-treated plants decreased over time and P. vera “Badami” plants showed significantly lower potentials than the other seedlings by 14 days after treatment. Water content was lower in 150 mM NaCl-treated plants than in 20% PEG because non-osmotic, perhaps toxic effects of NaCl increased cellular water loss. The data detected that ABA levels in P. atlantica subsp. mutica and P. vera “Badami” increased about 2-fold above the controls, but in P. vera “Sarakhs” it showed a 1.5-fold increase. ANOVA revealed that stomatal conductance measured on the same plants which were sampled for ABA levels in the xylem sap increased with the increase in salinity. These data suggest that xerophytic plants such as pistachio, which are adapted to arid environments, may show much reduced sensitivity in their ABA response system.
