Solute Accumulation in Tobacco Cells Adapted to NaCl

Abstract

Cells of Nicotiana tabacum L. var Wisconsin 38 adapted to NaCi (up to 428 millimolar) which have undergone extensive osmotic adjustment accumulated Na' and a-as principal solutes for this adjustment. Although the intracellular concentrations of Na' and a-correlated well with the level of adaptation, these ions apparently did not contribute to the osmotic adjustment which occurred during a culture growth cycle, because the concentrations of Na' and a-did not increase during the period of most active osmotic adjustment. The average intracellular concentrations of soluble sugars and total free amino acids increased as a function of the level of adaptation; however, the levels of these solutes did not approach those observed for Na' and a-. The concentration of proline was positively correlated with cell osmotic potential, accumulating to an average concentration of 129 millimolar in cells adapted to 428 millimolar Naa and representing about 80% of the total free amino acid pool as compared to an average of 0.29 millimolar and about 4% of the pool in unadapted cells. These results indicate that although Na' and aare principal components of osmotic adjustment, organic solutes also may make significant contributions.Osmotic adjustment is a fundamental adaptive response of plant cells which are exposed to salinity (8,11,26) and is necessary for survival and growth under saline conditions. Osmotic adjustment in response to salinity is a result of solute accumulation which occurs through the uptake of solutes, the synthesis of organic compounds, or both. The identification of solutes which accumulate in response to salinity is an initial step toward elucidating the biochemical and physiological mechanisms which are responsible for and regulate osmotic adjustment. Halophytes typically utilize Na+ and Cl-as principal osmotica (8,11,26), although organic solutes apparently serve an important role in balancing the osmotic pressure ofthe cytoplasm with that of the vacuole, into which much of the Na+ and Cl-is thought to be compartmentalized (8,26,28). In response to moderate levels of salinity, many glycophytic plants appear to exclude Na+ and Cl-as a mechanism of tolerance (21), using instead the synthesis and accumulation of organic compounds for osmotic adjustment (1 1, 28). However, the ability of glycophytic plants to accumulate Na+ and Cl-and survive high levels of salinity has not been investigated thoroughly.The in vitro isolation ofcells ofglycophytes with enhanced salt tolerance has helped facilitate the study of cellular responses to salinity ( 1-3, 15, 24). These salt tolerant cells are especially useful

Removal of Feedback Inhibition of Δ1-Pyrroline-5-Carboxylate Synthetase Results in Increased Proline Accumulation and Protection of Plants from Osmotic Stress

“…The activity of V. aconitifolia P5CS is reduced to 50% by 6 mm Pro (Hu et al, 1992). Plant cells under osmotic stress can accumulate up to 129 mm Pro in the cytosol (Binzel et al, 1987;, a concentration that would almost completely turn off the P5CS enzyme. This is contradictory to the fact that plants under stress continue to synthesize Pro and build up the Pro pool.…”

Intracellular Compartmentation of Ions in Salt Adapted Tobacco Cells

“…The extracts were frozen, lyophilized, and resuspended in 1 ml of H2O. Na+ and Cl-were measured as described previously (2). The radioactivity in the media samples and cell extracts was determined with a Beckman LS6800 liquid scintillation counter in 4 ml of aqueous counting cocktail (Aquasol, Amersham).…”

“…Na+ and Cl-, the principal components of the extensive osmotic adjustment exhibited by these cells, accumulated to an average whole cell concentration of 500 and 400 mm, respectively (2). Presented in this paper are results of an investigation utilizing steady state efflux kinetic analysis and scanning electron energy dispersive xray microanalysis to identify the intracellular localization of Na + and Cl-accumulated by cells adapted to 428 mM NaCl.…”

Enrichment of vitronectin‐ and fibronectin‐like proteins in NaCl‐adapted plant cells and evidence for their involvement in plasma membrane–cell wall adhesion

“…Unadapted tobacco (So) cells are usually plasmolyzed in 0.3 M NaCI, and spherical protoplasts, or convex membrane orientations, are observed within the cell wall (Figure la). Tobacco cells adapted to grow in medium containing 428 mM NaCl (S25) are osmotically adjusted and require more concentrated solutions to plasmolyze them (Binzel et al, 1985;lraki et al, 1989). Only after exposure to solutions much greater than 1 M do the plasma membranes pull away from their walls.…”

“…Additional isolines have since been selected that grow in as high as 3.5% NaCI. The adapted cells (S25) have a drastically altered growth physiology that results in much slower cell expansion, with fully expanded cells having volumes only one-fifth to one-eighth those of unadapted So cells (Binzel et a/., 1987). Several metabolic alterations have been identified that contribute to adaptation to the NaCl (Bressan eta/., 1987), and several alterations in the physical and chemical structure of the cell wall were identified as possible determinants of the altered tensile strength and extensibility associated with the severe growth limitation despite adequate turgor pressure (Iraki eta/., 1989).…”