Effects of High NaCl on Growth, Turgor and Internal Solutes of Tobacco Callus

Abstract

Responses of tobacco calluses to high NaCl were studied. A method was developed for washing the calluses and determining the volume of their free space using 14 C-sorbitol. Turgor pressures and concentrations of internal solutes could then be assessed. Exchange of ions between the agar medium and the free space of callus appeared to be slow. Therefore, concentrations of ions such as Na + , which tend to be excluded from the protoplast will increase in the free space of calluses. This accumulation makes the external NaCl and water potential (Ψ) of the individual cells of the calluses uncertain, so the assessed turgor pressure (P) is only a mean for the population of cells in the callus. Tobacco calluses selected for growth on culture medium containing 125 mol m −3 NaCl (Π of medium = 1.2 MPa) grew up to 15 % slower than unselected lines grown on culture medium without added NaCl (Π = 0.55 MPa). Turgor pressure (P) ranged between 0.2 and 0.7 MPa for cells grown at either low or high NaCl. Osmotic adjustment was mainly due to changes in internal Na + and Cl − , but sugars may have contributed about 35 % of osmotic adjustment in one line. The high concentrations of sugars in culture media might lead to preferential use of sugars for osmotic adjustment by the callus cells and if this trait were retained it may lead to decreased productivity of regenerated plants at high NaCl. In lines of cells selected for growth at high NaCl, Na + concentrations ranged between 70 and 190 mol m −3 and K + /Na + ranged between 0.12 to 0.74. Further work is required to establish how these differences between cell lines might relate to the ability of calluses and regenerated plants to grow at high NaCl.