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.