Salt accumulation and secretion patterns of Glycyrrhiza uralensis in saline habitats

Abstract

Although the leguminous plant Glycyrrhiza uralensis (licorice) is known to show strong salt tolerance, opinions are divided regarding the nature of its salt tolerance mechanisms. In this study, in order to gain an insight into the mechanisms underlying the adaptation of G. uralensis to saline environments, we investigated salt distribution patterns among the different organs of this plant, as well as the salt secretion characteristics of leaves. The results showed that large amounts of K+ and Ca2+ accumulated in the different organs of G. uralensis. K+ concentration was highest in young leaves, followed by that in roots and rhizomes, and was lowest in stems and old leaves. Ca2+ was mainly distributed in old leaves, and organ concentration tended to descend in the following order: old leaves, young leaves, stems, rhizomes, and roots. The concentration of Na+ within whole plants tended to be very low, whereas the amounts of Na+ secreted via leaves were significantly greater than those of K+ and Ca2+. Glycyrrhiza uralensis was thus found to be a potassium-accumulating calcicolous plant in which the absorption of Na+ is restricted by roots and absorbed Na+ is secreted in large amounts by leaves, thereby resulting in a very low accumulation of Na+ in all organs. Accordingly, these plants are characterized by high K+/Na+ and Ca2+/Na+ ratios, and we can conclude that selective absorption and secretion and the targeted accumulation of ions are important strategies in the adaptation of G. uralensis to saline habitats.