The Physiological and Biochemical Responses of a Medicinal Plant (Salvia miltiorrhiza L.) to Stress Caused by Various Concentrations of NaCl

Salvia miltiorrhiza, which is commonly known as Danshen, is a traditional Chinese herbal medicine. To illustrate its physiological and biochemical responses to salt stress and to evaluate the feasibility of cultivating this plant in saline coastal soils, a factorial experiment under hydroponic conditions was arranged on the basis of a completely randomised design with three replications. Five salinity treatments (0, 25, 50, 75 and 100 mM NaCl) were employed in this experiment. The results showed that salinity treatments of <100 mM NaCl did not affect the growth of Salvia miltiorrhiza in a morphological sense, but significantly inhibit the accumulation of dry matter. Salinity treatments significantly decreased the Chl-b content but caused a negligible change in the Chl-a content, leading to a conspicuous overall decrease in the T-Chl content. The Na(+) content significantly increased with increasing hydroponic salinity but the K(+) and Ca(2+) contents were reversed, indicating that a high level of external Na(+) resulted in a decrease in both K(+) and Ca(2+) concentrations in the organs of Salvia miltiorrhiza. Salt stress significantly decreased the superoxide dismutase (SOD) activity of Salvia miltiorrhiza leaves in comparison with that of the control. On the contrary, the catalase (CAT) activity in the leaves markedly increased with the increasing salinity of the hydroponic solution. Moreover, the soluble sugar and protein contents in Salvia miltiorrhiza leaves dramatically increased with the increasing salinity of the hydroponic solution. These results suggested that antioxidant enzymes and osmolytes are partially involved in the adaptive response to salt stress in Salvia miltiorrhiza, thereby maintaining better plant growth under saline conditions.