Factors Affecting Growth of Tobacco Callus Tissue and Its Incorporation of Tyrosine

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Abstract
The effect of varied concentrations of indoleacetic acid, kinetin, phosphate, and tyrosine on the growth and differentiation of tobacco callus tissue cultured in a liquid medium has been studied. The growth rate was influenced not only by the concentration, but also by the relative levels of each substance. It was observed that callus tissue produced buds and shoots when grown on a medium containing agar, and it produced only callus when supported at the surface of a liquid medium of the same composition. After fractionation of the callus tissue, 25-40% of the total cell N remained associated with the insoluble cell wall fraction. This fraction was separated further by extraction with formic acid into 2 fractions which differed in amino acid composition, rate of incorporation of tyrosine, and in the presence or absence of hydroxyproline. The significance of these results is discussed in terms of tissue growth. The incorporation of C14-labeled tyrosine into the tissue was demonstrated during a 24 hour period of incubation. In this time, 12.5% of the tyrosine in the soluble protein fraction had been replaced, 10.5% in the formmic acid soluble cell wall material and 2.2% in the cell wall residue. No other amino acid became radioactive after the tissue had been cultured in the presence of C14-labeled tyrosine for 24 hours.