Chitin-induced biosynthesis of phytoalexin 4'-deoxyaurone in cell suspension cultures of "old man" cactus, Cephalocereus senilis
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Cell suspension cultures of Cephalocereus senilis develop red pigmentation when infected by fungus. Previous work in our laboratory has established that chitin, a fungal cell wall component, can elicit the same response. These elicited cell cultures also produce several unusual flavonoids lacking the normal 4´-hydroxyl substitution in the B-ring, including the red pigment cephalocerone, a 4´-deoxyaurone. Previous enzymological studies showed that the elicited cell suspension cultures have the necessary enzymatic activities required for the conversion of L-phenylalanine to the 4´-deoxyflavonoids. Explanations for the 4´-deoxyflavonoid biosynthesis include (1) a bypass of cinnamic acid 4- hydroxylase therefore leading to an accumulation of 4´-deoxy precursors available for the 4´-deoxyflavonoid production and (2) a dehydroxylation step within the flavonoid biosynthetic pathway. The current biochemical investigations into the biosynthesis of the phytoalexin cephalocerone using HPLC metabolic profiling of isotope dilution experiments established the existence of a novel 4´-dehydroxylation step instead of a 4´-hydroxyl “bypass”. Our results strongly suggest that the metabolic flux involved in the selective production of 4´-deoxyflavonoids may be controlled by a specific enzyme activity that dehydroxylates the 4´-position of the tetrahydroxychalcone B-ring.