Precursors and the genetic control of pigmentation

Summary

The late block in the biosynthetic pathway to anthocyanin production in the corolla tubes of Antirrhinum majus caused by the mutation delila (del) can be circumvented by inoculation with live Botrytis cinerea. Pelargonidin or cyanidin was synthesised depending on the eosinea—Eosinea (Eos) constitution of the host. Other blocks in anthocyanin synthesis have not been overcome in this way. B. cinerea produced tube pigmentation in homozygous pallida-recurrens (pal-rec): del flowers only where pal-rec had mutated to Pal. Inoculation of B. cinerea to the intermediately blocked acyanic homozygous incolorata (inc) : del only initiated synthesis of cyanidin synergistically after administration of the absent dihydroflavonol, dihydroquercetin. Corolla tubes of inc Eos : del/inc Eos: del, inoculated and later homogenised and filtered to remove contaminating B. cinerea, initiated synthesis in Inc Eos : del/Inc Eos : del tubes; the heat labile agent was thus transferable from the non-anthocyanin producing acyanic host to one genetically capable of response, where anthocyanin was produced. Since the evidence was against B. cinerea providing an anthocyanin precursor or an enzyme, it is suggested that an enzyme stimulator was either formed in the A. majus corolla tubes or transferred from B. cinerea as a necessary stimulator for the enzyme that enabled the elaboration of the dihydroflavonol to anthocyanin.