The effect of salt stress and proline on some morphological, physical and phytochemical traits of leaf in three olive cultivars

Olive is one of the moderately resistant plants to salinity and the amount of resistance depends on the cultivar. Therefore, this species can be used as a model to study the responses of wooden plants to salt stress. In this study, six-months-old plantlets of three olive cultivars, including Arbequina, Arbosana, and Koroneiki were under salt stress through various concentrations of sodium chloride, containing 0, 50, 100, and 200 mM for five months, and sprayed with proline at 0, 100, and 200 mg/L for three times. At the end of the stress period, the number of leaves on each plant was counted; and thickness, length and width, and fresh and dry weight of the leaves were measured. Carotenoid content of leaves was determined using DMSO, total leaf phenol was measured by Folinciocalteu reagent, and glucose levels were estimated based on McCready. The results indicated that the number of leaves was decreased by increasing salinity levels and Arbosana had the greatest reduction. Koroneiki showed a significant reduction in leaf length and width at 200 mM and application of proline could not prevent this decline. The lowest fresh and dry weight was observed at 200 mM salinity. Leaf thickness was increased in the response of salt stress and the content of carotenoids reduced. Among the cultivars studied, Arbosana had the lowest total phenolic contents. Also, at salinity 200 mM, the highest and the lowest sugar content was observed in Arbosana and koroneiki, respectively. Plantlets treated with proline 200 mg/L had the highest carbohydrates.