Differential physiological and biochemical responses of three Echinacea species to salinity stress

The physiological and biochemical responses of the three Echinacea species, Echinacea purpurea, Echinacea pallida and Echinacea angustifolia were evaluated in response to NaCl salinity (0, 50, 75 and 100 mM) under hydroponic cultivation. Growth, injury index, gas exchange, ion accumulation, pigment content, electrolyte leakage (EL) in addition to antioxidant enzyme activities were measured after two weeks of salt treatments. Salinity did not alter the root or shoot biomass of the three Echinacea species studied. However, the survival rate varied among the species, with the highest rate (96.8%) in E. purpurea and the lowest one (70.7%) in E. angustifolia. In parallel, E. angustifolia plants showed high injury index and EL values compared to the other two species, which indicates its sensitivity to salinity-induced membrane damage even at the lowest salt concentration tested. This species showed a decrease in stomatal conductance, photosynthetic and transpiration rates at all salt concentrations; while, in E. purpurea and E. pallida, the photosynthetic rate was reduced only at 75 and 100 mM NaCl. The decline in the leaf gas exchange was highly correlated with Na+ and Cl- contents in all Echinacea species. Although Na+ and concentrations increased in both roots and shoots with increasing external salt concentrations, the accumulation of Na+ ions in E. angustifolia shoots was higher than in the other two species, resulting in a significant increase in Na+/K+ ratio. Furthermore, E. purpurea retained more Na+ ions in the roots than the other species suggesting higher efficiency in excluding Na+ from the shoots. E. purpurea showed increased superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities at all salt concentrations. On the other hand, salinity induced a reduction in catalase (CAT) activity with no change in glutathione reductase (GR) activity in any of the species. Our results indicate that the Echinacea species studied showed a limited salt tolerance. However, E. purpurea and to a lesser extent. E. pallida were more salt tolerant than E. angustifolia. The relative tolerance of E. purpurea was associated with the higher Na. exclusion capacity and the increased antioxidant activities particularly SOD and APX. (C) 2011 Elsevier B.V. All rights reserved.