Secondary metabolism in cultured red beet (Beta vulgaris L.) cells: Differential regulation of betaxanthin and betacyanin biosynthesis

Red beet cell lines exhibiting a range of cell colours were generated from secondary callus via specific induction methods. Phenotype colour ranged from white/green through yellow, orange and red to deep violet, representing all types of pigments found in red beet plant. Specific phenotypes could only be obtained through specific induction sequences and once established were stabilised by cultivation on a maintenance medium. The ratio of auxin (2,4-D) to cytokinin (6-BAP) was an important factor in the control of these processes. All coloured phenotypes were linked, but could be classified into two main groups, one yellow-red and the other orange-violet, according to their different cellular morphologies. A certain amount of instability still existed within each group. Modification of the growth regulator composition could be used to interchange specific combinations of coloured phenotypes, depending upon the initial state of cellular differentiation. Use of the DNA-methylation inhibitor 5-azacytidine demonstrated that methylation plays a key role in the repression of genes encoding enzymes involved in betacyanin biosynthesis. Furthermore, the poly(ADP-ribose) polymerase inhibitor 3-methoxybenzamide blocked the induction of the same gene set in a concentration dependent manner without affecting cell growth.