Plasma Membrane Na+ Transport in a Salt-Tolerant Charophyte (Isotopic Fluxes, Electrophysiology, and Thermodynamics in Plants Adapted to Saltwater and Freshwater)

Abstract

In salt-tolerant Chara longifolia, enhanced Na+ efflux plays an important role in maintaining low cytoplasmic Na+. When it is cultured in fresh water (FW), C. longifolia has a higher Na+ efflux than the obligate FW Chara corallina, although pH dependence and inhibitor profiles are similar for both species (1. Whittington and M.A. Bisson 119941 j Exp Bot 45: 657-665). When it is cultured in saltwater, C. longifolia has a Na+ efflux of 264 f 14 nmol m-'s-' at pH 7, 13 times higher than FW-adapted cultures and 31 times higher than C. corallina. As in FW-adapted plants, efflux is highest at pH 5, but pH dependence is less steep and more linear in cells adapted to saltwater. In plants of both species from FW cultures, Na+ efflux is inhibited by Li+ at pH 5 but not at pH 7 or 9, whereas in the salt-adapted C. longifolia, Li+ inhibits Na+ efflux at pH 7 and 9 but not at pH 5. Amiloride inhibits Na+ efflux in salt-adapted cells but not in FW cells. We conclude that a new type of Na+ efflux system is induced in salt-adapted plants, although both systems have characteristics suggestive of a Na+/H+ antiport. In all cases, a 1 :1 Na+/H+ antiport would have sufficient energy to maintain the cytoplasmic Na+ activities measured at pH 5 and 7 but not at pH 9, which suggests that another efflux system must be operating at p H 9.

Sodium-Dependent Nitrate Transport at the Plasma Membrane of Leaf Cells of the Marine Higher PlantZostera marinaL.

“…More accurate cytosolic measurements in non-marine plants give values of 3 to 5 mm for NO 3 Ϫ in barley root epidermal cells (Walker et al, 1995;van der Leij et al, 1998) and 50 mm for Na ϩ in a salttolerant Chara species (Kiegle and Bisson, 1996). (Although total internal Na ϩ concentrations have been estimated in two species of seagrass, being around 100 mm in epidermal leaf cells and showing higher values in other tissues [Beer et al, 1980], such estimates will reflect primarily the composition of the large central vacuole rather than that of the cytosol.)…”

Toxin content differs between life stages of Alexandrium fundyense (Dinophyceae)

“…Sodium transport ports occur in bacteria, animals, fungi and mosses (Benito and Rodriguez-Navarro, 2003) and are presumed to occur in all marine protists, although very few studies have been done to confirm this assumption. Sodium-transport ports have been studied in the raphidophyte Heterosigma akashiwo (Shono et al, 2001), the chytridomycete Blastocladiella emersonii (Fietto et al, 2002), and the macroalga Chara longifolia (Kiegle and Bisson, 1996). Sodium-transport physiology has also been studied in the freshwater cyanobacterium Cylindrospermopsis raciborskii (Pomati et al, 2003(Pomati et al, , 2004.…”

Mechanisms underlying turgor regulation in the estuarine alga Vaucheria erythrospora (Xanthophyceae) exposed to hyperosmotic shock

“…). Studies with radioactive Na + isotopes and amiloride have shown both salt‐tolerant C. longifolia and salt‐sensitive C. corralina to actively extrude Na + through Na + /H + antiporters (Clint & MacRobbie ; Kiegle & Bisson ). Halophilic green algae like Dunaliella viridis and D. salina also actively extrude Na + and accumulate glycerol in the cytosol for osmotic adjustment (Katz et al .…”

“…Their euryhaline species regulate turgor by taking up K + and Cl − while Na + only plays a minor role in the process. In the characean algae, Na + is actively extruded from the cytosol by a Na + /H + antiporter (Bisson & Kirst ; Kiegle & Bisson ; Bisson et al . ).…”