Regulation by ABA of osmotic-stress-induced changes in protein synthesis in tomato roots

Polypeptide synthesis and accumulation were examined in the roots of tomato seedlings exposed to a polyethylene glycol-imposed water deficit stress. I n these roots, the synthesis of a number of polypeptides was induced, while that of several others was enhanced or repressed. To examine the role play ed by abscisic acid (ABA) in co-ordinating the accumulation of these protei ns, water-deficit-stress-responsive polypeptide synthesis was investigated in the roots of the ABA-deficient mutant flacca. In the roots of this mutan t, the ability to accumulate a complete set of water-deficit-stress-respons ive polypeptides was impaired, indicating that ABA is required for their sy nthesis. The role of ABA was further examined by exposing the roots of both genotypes to exogenous ABA, which, with one exception, elicited the accumu lation of all water-deficit-stress-responsive proteins. Polyethylene glycol -induced polypeptide accumulation was accompanied by a 1.6-fold increase in the level of endogenous ABA in the roots of wild-type plants and a 5-fold increase in the roots of flc. Thus, although the absolute level was lower t han that of the wild-type, flc has the capacity to accumulate ABA in its ro ots. When fluridone was used to prevent the biosynthesis of ABA, the accumu lation of several water-deficit-stress-responsive polypeptides was reduced further. The synthesis of polypeptides was also examined in the roots of sa lt-treated seedlings. Salt altered the accumulation of several polypeptides , all of which were previously observed in water-deficit-stressed roots, in dicating that their synthesis was the result of the osmotic component of th e salt stress. However, the accumulation of these polypeptides was not impa ired in flc roots, indicating that the role played by ABA in regulating the ir accumulation in salt-and polyethylene glycol-treated roots differs. As s uch, salt- and water-deficit-stress-induced changes in gene expression may be effected by different mechanisms, at least at the level of polypeptide a ccumulation.