Inhibition by Cytokinin of the Accumulation of Betacyanin in Suspension Cultures of Phytolacca americana

The accumulation o f betacyanin was reduced by the addition o f various cytokinins to sus­ pension cultures o f Phytolacca americana. The decrease in the accumulation o f betacyanin was overcome by exogenously supplied tyrosine which is a precursor o f betacyanin. Benzylaminopurine (BAP) decreased the level o f free tyrosine in the cells. Feeding experiments using labeled tyrosine revealed that BAP reduced the incorporation o f labeled tyrosine into betacyanins (to about 50% o f the control rate). These results suggest that both the availability o f tyrosine and the biosynthetic activity o f the pathway from tyrosine to the betacyanins are involved in the inhibition o f the accumulation o f betacyanins by cytokinins in Phytolacca americana cells.