Ability of multicellular salt glands in Tamarix species to secrete Na+ and K+ selectively

The present study aimed to determine the mechanism of cation-selective secretion by multicellular salt glands. Using a hydroponic culture system, the secretion and accumulation of Na+ and K+ in Tamarix ramosissima and T. laxa under different salt stresses (NaCl, KCl and NaCl+KCl) were studied. Additionally, the effects of salt gland inhibitors (orthovanadate, Ba2+, ouabain, tetraethylammonium (TEA) and verapamil) on Na+ and K+ secretion and accumulation were examined. Treatment with NaCl (at 0–200 mmol L−1 levels) significantly increased Na+ secretion, whereas KCl treatment (at 0–200 mmol L−1 levels) significantly increased K+ secretion. The ratio of secretion to accumulation of Na+ was higher than that of K+. The changes in Na+ and K+ secretion differed after adding different ions into the single-salt solutions. Addition of NaCl to the KCl solution (at 100 mmol L−1 level, respectively) led to a significant decrease in K+ secretion rate, whereas addition of KCl to the NaCl solution (at 100 mmol L−1 level, respectively) had little impact on the Na+ secretion rate. These results indicated that Na+ secretion in Tamarix was highly selective. In addition, Na+ secretion was significantly inhibited by orthovanadate, ouabain, TEA and verapamil, and K+ secretion was significantly inhibited by ouabain, TEA and verapamil. The different impacts of orthovanadate on Na+ and K+ secretion might be the primary cause for the different Na+ and K+ secretion abilities of multicellular salt glands in Tamarix.