Abscisic Acid Stimulated Osmotic Adjustment and Its Involvement in Adaptation of Tobacco Cells to NaCl

Abstract

Osmotic adjustment of cultured tobacco (Nicotiana tabacum L. var Wisconsin 38) cells was stimulated by 10 micromolar (+/-) abscisic acid (ABA) during adaptation to water deficit imposed by various solutes including NaCl, KCl, K(2)SO(4), Na(2)SO(4), sucrose, mannitol, or glucose. The maximum difference in cell osmotic potential (Psipi) caused by ABA treatment during adaptation to 171 millimolar NaCl was about 6 to 7 bar. The cell Psipi differences elicited by ABA were not due to growth inhibition since ABA stimulated growth of cells in the presence of 171 millimolar NaCl. ABA caused a cell Psipi difference of about 1 to 2 bar in medium without added NaCl. Intracellular concentrations of Na(+), K(+), Cl(-), free amino acids, or organic acids could not account for the Psipi differences induced by ABA in NaCl treated cells. However, since growth of NaCl treated cells is more rapid in the presence of ABA than in its absence, greater accumulation of Na(+), K(+), and Cl(-) was necessary for ion pool maintenance. Higher intracellular sucrose and reducing sugar concentrations could account for the majority of the greater osmotic adjustment of ABA treated cells. More rapid accumulation of proline associated with ABA treatment was highly correlated with the effects of ABA on cell Psipi. These and other data indicate that the role of ABA in accelerating salt adaptation is not mediated by simply stimulating osmotic adjustment.

Stable NaCl Tolerance of Tobacco Cells Is Associated with Enhanced Accumulation of Osmotin

“…Additional circumstantial evidence which supports this concept is as follows: (a) Treatment of the cells with ABA induces synthesis of the osmotin form that accumulates in NaCladapted cells (25) and is correlated with ABA accelerated adaptation (growth) of tobacco cells to a newly imposed NaCl stress (15,16 …”

“…Unadapted cells synthesize mainly a cross-reacting protein with a lower apparent pI of 7.8 (25) but accumulate low levels of both forms. The synthesis of osmotin in tobacco cells and cells of proso millet, field bindweed, cotton, carrot, and potato is induced by ABA (25), a treatment that accelerates adaptation of tobacco cells to stress induced by ionic solutes (15) and hastens osmotic adjustment in response to water deficits imposed by ionic and nonionic solutes ( 16).…”

Characterization of a rice gene showing organ-specific expression in response to salt stress and drought.

“…Abscisic acid also increases in osmotically stressed plants (Steward and Voetberg, 1985) and can induce, when applied exogenously, biochemical changes ' To whom correspondence should be addressed. similar to those produced by salt (LaRosa et al, 1987). Such experiments have led to the conclusion that this hormone may normally be used to control part of the adaptation process.…”

“…Within 15 min of exposure to saline conditions, an Na+/H+ exchange process is activated so that K+ can be pumped across the cell membrane (Watad et ai., 1986) and Na+ can be pumped into tonoplasts (Binzel et al, 1988;Garbarino and DuPont, 1989). Over the course of several days, the ratio of glycolipids to phospholipids can increase (Hirayama and Mihara, 1987), permitting more solutes to enter the cell and thus facilitate water entry, while the overall concentration of osmoprotectants including sugars, proline, and organic acids rises (Binzel et al, 1987;LaRosa et al, 1987). Abscisic acid also increases in osmotically stressed plants (Steward and Voetberg, 1985) and can induce, when applied exogenously, biochemical changes ' To whom correspondence should be addressed.…”

Enhanced Net K+ Uptake Capacity of NaCl-Adapted Cells

“…Concentrated solutions of salts were added to cell suspensions to achieve the desired ion concentrations. Viability was based on the percent of cells that included neutral red (13). Cell osmotic potentials were measured by determining incipient plasmolysis in NaCl solutions graded at 0.05 molal increments (1 1).…”