Proteins associated with salt adaptation in citrus and tomato cells: Involvement of 26 kDa polypeptides

Stress-induced changes in proteins of molecular weights of 25 and 27 kDa are reported for NaCl-adapted cells of Shamouti orange ( Citrus sinensis L. Osbeck) and the cultivated VFNT cherry tomato ( Lysopersicon esculentum Mill.), respectively. Salt-adapted cell lines of both species grew much faster in the presence of salt than non-adapted cells and their growth rate was similar to that of non-adapted cells in the absence of salt. Sodium dodecyl sulfate-extractable citrus and tomato polypeptides were analyzed by one- and two-dimensional polyacrylamide gel electrophoresis (PAGE). The enhancement of a citrus 25 kDa protein associated with salt tolerance was actually resolved only on two-dimensional PAGE. It is a constitutive protein, i.e. it was present in salt-tolerant ceils whether grown in the presence or absence of salt. The NaCl-induced changes of the tomato 27 kDa protein could be resolved on one-dimensional PAGE. This protein was first markedly suppressed by a salt shock and the time required for its recovery was dependent on the degree of salt tolerance. Prolonged adaptation resulted in an increase of this protein. Protein profiles of citrus and tomato cells grown in the absence and presence of salt revealed that while in citrus the level of most proteins was suppressed in the presence of salt, the opposite was true for tomato proteins under similar conditions. Comparison between the changes in citrus and tomato and results already published for tobacco show that many salt-induced changes in proteins are species-specific and that no obvious similarities exist.