Growth, physiological, biochemical and ionic responses of pistachio seedlings to mild and high salinity

Depending on salt concentrations, different mechanisms are involved in the tolerance of pistachio and an acclimation to salinity conditions occurs in the leaves that develop in the presence of salt. Pistachio (Pistacia vera L.) is a salt tolerant species that is considered an alternative crop for cultivation in salinzied orchard soils. In this work, 12-week-old pistachio seedlings cultivated in soil under greenhouse conditions were treated with five levels of salinity including control (0.63 dSm(-1)), low (2 and 4 dSm(-1)) and high (8 and 10 dSm(-1)) salt concentrations for further 12 weeks. Plant growth parameters were not affected by mild salinity; a significant reduction was only observed from 8 dSm(-1). Considerable differences were observed between the young and mature leaves regarding osmotic and ionic stress effects of salt. Main compatible solutes were proline in mature leaves, proline and soluble sugars in young leaves, and soluble sugars and amino acids, other than proline, in roots. Concentration and content of Na in the leaves were not significantly increased at low levels of salinity and the K:Na and Ca:Na ratio of leaves were affected only by higher salt concentrations. Using the sequential extraction procedure for cell wall isolation, we observed that both absolute and relative amounts of Na in the cell wall fraction increased under low salinity, while decreased under higher levels of salt supply. Stable water relations, photochemistry and CO2 assimilation rates particularly of young leaves, as well as ion homeostasis were mechanisms for maintenance of plants growth under mild salinity. Under severe saline conditions, the impaired ability of mature leaves for synthesis of assimilates, preferent allocation of carbohydrates to roots for maintenance of osmotic homeostasis and finally, reduction of protein synthesis caused growth inhibition in pistachio.