Involvement of the hormone abscisic acid and the protein osmotin in the adaptation of Nicotiana tabacum L. cells to salinity

Paul Christopher LaRosa, Purdue University

Abstract

These studies were performed to determine if abscisic acid (ABA) regulates adaptive responses of plant tissues to NaCl stress. ABA enhanced the growth of unadapted cells of tobacco (Nicotiana tabacum L.) in medium with NaCl but did not increase the growth of cells previously adapted to NaCl unless the cells were inoculated into medium with a level of NaCl higher than the level to which the cells were adapted. The growth of unadapted cells in medium containing other ionic solutes, but not nonionic solutes was also stimulated by ABA. However, osmotic adjustment of tobacco cells was stimulated by ABA during adaptation to water deficit imposed by both ionic and nonionic solutes. The cell $\psi\sb{\pi}$ differences elicited by ABA were not due to growth inhibition since ABA stimulated growth of cells in the presence of NaCl. Higher intracellular sugar concentrations, but not other major solutes 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 $\psi\sb{\pi}$. These results indicate that ABA is specifically involved in adaptation of cells to salts, but not by simply stimulating osmotic adjustment. Osmotin is a major protein which is synthesized in response to ABA, that accumulated in cells of tobacco, tomato and potato adapted to low cell $\psi\sb{\pi}$ and which accumulated in NaCl-treated plant tissues. Osmotin continued to accumulate at increased levels after NaCl-adapted cells were grown in the absence of NaCl for many cell generations. A ten-fold increase in osmotin, which had an apparent pI of $>8.2$, occurred in cells adapted to 428 mM NaCl. Upon transfer to medium without NaCl and subsequent growth for many cell generations, osmotin levels declined gradually over many cell generations to a level intermediate between that found in adapted and unadapted cells. Adapted cells grown in the absence of NaCl exhibited absolute growth rates and NaCl tolerance levels which were intermediate to those of NaCl-adapted and unadapted cells. The association between osmotin accumulation and stable NaCl tolerance as well as other evidence, suggests a role for this protein in adaptation to low $\psi\sb{\pi}$.

Degree

Ph.D.

Advisors

Bressan, Purdue University.

Subject Area

Botany

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