Background A longstanding question in plant physiology concerns the mechanisms of Na+ stress in plants (see Plant Nutrition and Salinity Stress). Most plants are salt sensitive (glycophytes), and the presence of large amounts of Na+ is inhibitory to growth (but low levels of Na+ are often stimulating growth). In contrast, growth of halophytic plants is stimulated by NaCl and halophytes can survive in saline habitats such as salt marshes and coastal regions.
Whereas uptake of Na+ into plants is 'passive' many plant nutrients have to be imported into the root against their (electro)chemical gradient and therefore require an 'active' transport system. Most active transport systems in plants are energised via coupling to H+ transport. However, energisation through coupling to Na+ transport has also been described for uptake of K+, nitrate and urea, but only appears to be present in aquatic species (1;2). In addition, recent data indicate that in marine halophytic species Na+-coupled NO3 uptake occurs (4).
Project aims The occurrence of Na+ coupled transport in aquatic species and its absence in (most) terrestrial glycophytes is highly relevant for the ecophysiology of these plants. The aim of this project would be to study whether Na+ coupled transport is present in halophytic (terrestrial) plants, and what the ecophysiological implications are in comparison to glycophytic plant.
Methods Initially, plant growth and ionic contents will be studied in conditions that differ in salinity status. Electrophysiological techniques (e.g. Patch Clamping ) are ideal to study membrane transport, and this project will involve measuring membrane potentials in roots of halophytes to assess the presence of Na+ coupled transport. In addition, fluxes of Na+ and other nutrients will be determined to characterise and quantify transport.
References:
(1) Walker et al (1991) Planta 185, 443-445
(2) Maathuis et al (1996) Plant Physiol 112,1609-1616
(3) Walker et al (1996) Science 373, 977-978.
(4) Garcia-Sanchez et al (2000) Plant Physiol 122, 879-885