Na compartmentalisation in Salicornia

The tonoplast Na + /H + -antiporter and the tonoplast H + -pumps are essential components of salt tolerance in plants. The objective of this study was to investigate the transport activities of the tonoplast Na + /H + -antiporter and the tonoplast V-H + -ATPase and V-H + -PPase in a highly tolerant salt accumulating halophyte, Salicornia dolichostachya, and to compare these transport activities with activities in the related glycophyte Spinacia oleracea. Vacuolar membrane vesicles were isolated by density gradient centrifugation, and proton transport and hydrolytic activity of both H + -pumps were studied. Furthermore, the Na + /H + -exchange capacity of the vesicles was investigated by ACMA fluorescence. Salt treatment induced V-H + -ATPase and VH + -PPase activity in vesicles derived from S. oleracea, whereas V-H + -ATPase and V-H + -PPase activity in S. dolichostachya was not affected by salt treatment. Na + /H + -exchange capacity followed the same pattern, i.e. induced in response to salt treatment (0 and 200 mM NaCl) in S. oleracea and not influenced by salt treatment (10 and 200 mM NaCl) in S. dolichostachya. Our results suggest that S. dolichostachya generates a high tonoplast H + -gradient already at low external salinities, which is likely to contribute to the high cellular salt accumulation of this species at low external salinities. At high external salinities, S. dolichostachya showed improved growth compared to S. oleracea, but V-H + -ATPase, V-H + -PPase and Na + /H + -exchange activities were comparable between the species, which might imply that S. dolichostachya more efficiently retains Na + in the vacuole.