Fast growth responses of barley and durum wheat plants to NaCl- and PEG-treatment: resolving the relative contributions of water deficiency and ion toxicity

Abstract

Effects of adding osmotically comparable concentrations of PEG and NaCl to nutrient solution were studied in 1-week-old durum wheat (Triticum durum Desf., salt-sensitive) and barley (Hordeum vulgare L., more salt tolerant). Both treatments arrested leaf extension immediately, followed by partial recovery within 40–60 min. Similarities and differences were observed between the responses of the two species and between the two treatments. Typically, PEG-treatment increased leaf extensibility of both barley and wheat as measured by changes in leaf extension rate monitored by an electromechanical sensor to which a stretching counter-weight was added. In barley, NaCl-treatment increased extensibility in a similar way to PEG, but in wheat, extensibility did not change within 40 min of NaCl-treatment. The contrasting fast responses of wheat plants to NaCl and PEG treatments suggests that, unlike barley, wheat leaf extension was sensitive not only to osmotic effects of salinity, but also to ion toxicity. Thus, separate PEG- and NaCl-treatments enabled us to distinguish between ionic and osmotic effects and to show, for the first time, that ionic effects of salinity on leaf extension can commence after only short-term exposure (<1 h) in the case of a salt-sensitive species such as durum wheat.