Hormonal regulation of protein synthesis associated with salt tolerance in plant cells.

Cultured tobacco cells (Nicotiana tabacum L. cv. Wisconsin 38) synthesize a predominant 26-kDa protein upon exposure to abscisic acid (ABA). ABA also accelerates the rate of adaptation of unadapted cells to NaCl stress. The ABA-induced 26-kDa protein is immunologically cross-reactive to, and produces a similar pattern of peptides after partial proteolysis as, the major 26-kDa protein associated with NaCl adaptation. Both have pI values of >8.2. The synthesis of the ABA-induced 26-kDa protein is transient unless the cells are simultaneously exposed to NaCl stress. There is an association between increased intracellular accumulation of ABA during cell growth and commencement of synthesis of the 26-kDa protein. ABA induces the synthesis of an immunologically cross-reactive 26-kDa protein in cultured cells of several plant species. In tobacco plants, synthesis of the 26-kDa protein could be detected in several tissues but the highest level of expression was seen in outer stem tissue. In root tissues, exogenous ABA greatly stimulated the synthesis of 26-kDa protein as compared to outer stem tissue and leaf. We suggest that ABA is involved in the normal induction of the synthesis of 26-kDa protein and that the presence of NaCl is necessary for the protein to accumulate.