Ability of salt glands in Rhodes grass (Chloris gayana Kunth) to secrete Na+ and K+

Some plants are able to tolerate salinity using salt glands on the leaf surface, which secrete excess salts transported into the leaves. Rhodes grass (Chloris gayana Kunth) reportedly possesses such salt glands, but the features of secretion remain unclear. In the present study, we compared the ability of Rhodes grass salt glands to secrete sodium and potassium with the aim of clarifying the preference of cations for secretion. In both whole plant experiments and detached leaf experiments, NaCl treatment increased Na+ secretion and KCl treatment increased K+ secretion. When the ratios of the amount of secreted ions to their concentration in the leaves were compared between Na+ and K+, the ratio was greater with Na+ than K+. The addition of NaCl to the KCl solution significantly decreased K+ secretion, but the addition of KCl to the NaCl solution did not have a significant effect on Na+ secretion. These results indicate that the salt glands of Rhodes grass can secrete both Na+ and K+, but the ability to secrete Na+ is greater than that of K+ secretion. To examine the secretion mechanisms, various ion transport inhibitors were applied to detached leaves. All five inhibitors examined (orthovanadate, barium [Ba2+], ouabain, tetraethylammonium [TEA] and verapamil) significantly inhibited Na+ secretion, but only three inhibitors (ouabain, TEA and verapamil) inhibited K+ secretion. These results indicate that the secretion mechanisms of Na+ and K+ differ in Rhodes grass, at least partially, possibly resulting in the different secretion abilities of Na+ and K+.