Salt-induced protein synthesis in tomato roots: the role of ABA

The role played by abscisic acid (ABA) in regulating salt-induced protein s ynthesis was investigated in roots of tomato (Lycopersicon esculentum Mill. cv, Ailsa Craig). Roots of 9-d-old Ailsa Craig (AC) seedlings and the near -isogenic ABA-deficient mutant, flacca (flc), were exposed to salt which el icited the appearance of novel polypeptides and both repressed and enhanced the synthesis of others. The polypeptide profiles of salt-treated AC and f lc roots were similar suggesting that the synthesis of most novel polypepti des in salt-treated roots is not dependent on an elevated level of endogeno us ABA. Exogenous ABA and a combined ABA/salt treatment were applied to the roots of AC and flc. Exogenous ABA, in the absence of salt, induced the ac cumulation of several polypeptides that were unique to this treatment as we ll as a subset of those synthesized in salt-treated roots. Interestingly, i n roots exposed to the combined ABA/salt treatment, only those polypeptides that accumulated in both ABA or salt-treated roots were synthesized. Endog enous ABA levels increased 2-fold in salt-treated AC roots and 14-fold in s alt-treated flc roots. Although the absolute level of ABA was lower in salt -treated flc than in AC, this demonstrates that flc has the capacity to acc umulate some ABA in its roots following a salt treatment. Since it is possi ble that this level of ABA was sufficient to induce the changes in polypept ide synthesis observed in salt-treated roots of flc, the salt-induced accum ulation of endogenous ABA was prevented by treating AC roots with fluridone . In these roots, the set of salt-induced polypeptides was similar to that observed in salt-treated roots indicating that an elevated level of endogen ous ABA may not play a major role in regulating the accumulation of most sa lt-induced proteins in tomato roots.