Control of salt transport from roots to shoots of wheat in saline soil

Abstract

Wheat genotypes with 5-fold difference in shoot Na+ concentrations were studied over a salinity range of 1–150 mm NaCl and CaCl2 of 0.5–10 mm to assess their performance in saline and sodic soils. All genotypes had a maximum shoot Na+ concentration at 50 mm external NaCl when the supplemental Ca2+ provided an activity of 1 mm or more. Shoot Na+ concentrations either stayed constant from 50 to 150 mm external NaCl, or decreased in some genotypes at the higher salinity. Calculated rates of root uptake, and root : shoot transport, were at a maximum at 50 mm NaCl in all genotypes, and decreased at higher NaCl in some genotypes, indicating feedback regulation. K+ showed a pattern inverse to that of Na+. Cl– uptake and transport rates increased linearly with increasing salinity, and differed little between genotypes. Increasing external Ca2+ concentration reduced the accumulation of Na+ in the shoot, the effects being greater in the low Na+ genotypes, and greater as the salinity increased, indicating that the plateau in shoot Na+ concentration relied on the maintenance of a minimal Ca2+ activity of 1 mm. Increasing external Ca2+concentration did not reduce the root Na+ concentration, however, suggesting that Ca2+ influenced the loading of Na+ in the xylem.