NA+/H+ ANTIPORT ACTIVITY IN TONOPLAST VESICLES FROM ROOTS OF THE SALT-TOLERANT PLANTAGO-MARITIMA AND THE SALT-SENSITIVE PLANTAGO-MEDIA

Plantago species differ in their strategy towards salt stress, a major difference being the uptake and distribution of Na+ ions. A salt-sensitive (Plantago media L.) and a salt-tolerant (P. maritima L.) species were compared with respect to Na+/H+ antiport activities at the tonoplast. After exposure of the plants to 50 mM NaCl for 6 days isolated tonoplast vesicles of P. maritima showed Na+/H+ antiport activity with saturation kinetics and a K(m) of 2.4 mM Na+ . NaCl-grown P. media and the control plants of both species showed no antiport activity. Selectivity of the antiport system for Na+ was high and was determined by adding different chloride salts after formation of a DELTA-pH in the vesicles. Specific tonoplast ATPase activities were similar in the two species and did not alter after exposure to NaCl stress.