Salt secretion in Rhodes grass (Chloris gayana Kunth) under conditions of excess magnesium

Abstract

Rhodes grass (Chloris gayana Kunth) is known to be a salt-tolerant grass, and its tolerance is related to the presence of salt glands that secrete excess salts transported into the leaves. The salt glands of Rhodes grass reportedly have a high ability to secrete Na+, but their ability to secrete Mg2+ remains unclear. In the present study, we examined salt secretion via the salt glands under conditions of excess Mg2+ using both whole plants and detached leaves of Rhodes grass. MgCl2 treatment significantly increased Mg2+ secretion, but the extent of secretion remained relatively minor. MgCl2 treatment significantly increased K+ secretion, and the increase in K+ secretion was more than 50-fold higher than the increase in Mg2+ secretion. The increase in K+ secretion caused by MgCl2 treatment was inhibited by the application of ion transport inhibitors. Inhibition of K+ secretion amplified the increase in leaf sap osmolality caused by MgCl2 treatment. These results indicate that: (1) salt glands of Rhodes grass have a low ability to secrete Mg2+, (2) salt glands of Rhodes grass substitute K+ secretion for Mg2+ secretion under conditions of excess Mg2+, (3) substitutive K+ secretion may play a role in the alleviation of osmotic changes caused by Mg2+ accumulation.