Changes in callus growth, differentiation potency and protein profile induced by salt stress were investigated in the calli induced from a hypocotyl of Robinia pseudoacacia L. The NaCl treatment evidently obstructed the callus growth and the influences seemed to continue to be present in the selected calli even after they were restored in NaCl-free medium that could partially recover the callus growth, and some polypeptides were found to restore. The calli selected and restored intermittently every two weeks for one year completely lost their differentiation potency. The NaCl-tolerance test of the regenerated plantlets revealed that part of the plantlets that directly regenerated from the selected NaCl-tolerant calli were able to survive in 0.2 M NaCl, while most of the plantlets regenerated from the NaCl-nonselected calli or from restored calli were obviously damaged by this treatment. The SDS-PAGE assay indicated that a 54 kDa polypeptide increased distinctly to a very high level while a 41 kDa polypeptide decreased to a lower level in almost all the NaCl-tolerant plantlets. This observation led to the suggestion that the changes may play an adaptive role in allowing plantlets to survive under saline conditions.
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