Induction of phenylpropanoid pathway enzymes in elicitor-treated cultures of Cephalocereus senilis

Treatment of old-man-cactus (Cephalocereus senilis) suspension cultures with chitin elicits synthesis of an aurone phytoalexin, cephalocerone. Elicitor-induced de novo synthesis of cephalocerone was demonstrated by incubating elicited cactus cultures with [³H]phenylalanine; this resulted in the labelling of five induced phenolic compounds including cephalocerone. Increased extractable activities of the phenylpropanoid pathway enzymes phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS) and chalcone isomerase (CHI) accompanied the synthesis of cephalocerone. CHS and PAL, which are both involved in the biosynthesis of cephalocerone, showed maximum activity at 12 and 24 hr post-elicitation, respectively. CHS and CHI activities catalysing the synthesis and subsequent isomerization of 2′,4′,6′-trihydroxychalcone were present in the cell cultures, consistent with the formation of cephalocerone via a chalcone with no B-ring substituents.