Biochemical Studies on the Terpene Metabolism in Sweet Potato Root Tissue with Black Rot

Using sweet potato root tissue infected with Ceratocystis fimbriata, the effect of farnesol, nerolidol or geraniol on the incorporation of acetate-2-14C into ipomeamarone and other lipids, and on the production of ipomeamarone and other lipids was examined.Acetate-2-14C incorpration into ipomeamarone and other lipids and the production of the lipids except ipomeamarone were markedly suppressed by the addition of the terpenol.The production of ipomeamrone was unaffected.It was concluded that the marked decrease of acetate incorporation into ipomeamarone in the presence of the terpenol was due mainly to the direct inhibition of the biosynthetic pathway and to a lesser extent to their dilution effect.The inhibitory sites by the terpenol seemed to be localized in at least 2 positions in the biosynthetic pathway of ipomeamarone.After feeding tissue disks with actetate-2-14C in the presence of farnesol or geraniol, either farnesol or geraniol was isolated, and the respective crystalline derivatives were found to be radioactive.Sweet potato root tissue, when infected with Ceratocystis fimbriata (E. and H. Elliot), turns black-brown and produces and accumulates a large amount of furanoterpenoids such as ipo meamarone (I) and ipomeanine (II)* in the in fected region of the tissue.""This phenomenon is one of the typical symptoms of the disease and is involved in an important defense ma chanism of the host.These compounds exhibit a potent antifungal action against the invading fungus,"" and the amounts produced by various varieties of sweet potato reflect the degree of the resistance of the varieties against the fun gus."""Also, this type of defense mecha nism was further supported by the observation * This paper constitutes Part 68 of the Phyto pathological Chemistry of Sweet Potato with Black Rot and Injury.