Abstract: Comparative study on the subcultured callus of tobacco (Nicotiana tabacum L. cv. Willow leaf) has revealed that protein contents and pr otease activities slowly decreased in the callus during differentiation and bud formation. The synthetic rates of fraction Ⅱ protein (water soluble protein and enzymes) and ribosomal hist one, the levels of total ribosomes, especially the levels of polyribosomes which function the protein synthesis, were higher in the differentiating callus than those in the subcultured callus. This indicates that protein synthesis in differentiating callus is greater than that in non-differentiating callus, and that the protein pattern synthesized in differentiating callus may differ from that in non-differentiating callus. During the late period of culture, the protease activities in subcultured callus rapidly increased, and the levels of polyribosomes, protein synthetic rates and protein contents apparently declined, which may be the result of metabolic changes in callus senescence. Meanwhile in the differentiating callus the protein contents, protein synthesis rates and polyribosome levels although somewhat declined accempanying the growth of formed bud, were still much higher than those in the subcultured callus.

Key words: Tobacco callus, Subculture, Tissue differentiation, Protein synthesis, Polyribosome population