Apparent energy deficiency in mono- and sesqui-terpene biosynthesis in peppermint

Abstract Radioactivity from mevalonate-2- 14 C is incorporated into the mono- and sesqui-terpenes of peppermint ( Mentha piperita L.) cuttings when this precursor is fed through the cut stems. When unlabeled sucrose is fed along with labeled mevalonate, the incorporation of mevalonate into mono- and sesqui-terpenes is markedly increased, the turnover period of the labeled terpenes is extended by with little change in turnover rate, and the proportion of label in the two major sesquiterpenes is shifted. These results are discussed in relation to the morphology of peppermint secretory structures and in relation to possible compartmentalization of mono- and sesqui-terpene biosynthesis within these structures, and it is suggested that sucrose may be satisfying an energy requirement at the biosynthetic sites. Exposure to 5% CO 2 in the light, coupled with mevalonate-2- 14 C feeding, produces results similar to the co-administration of sucrose. The addition of unlabeled sodium acetate slightly increases incorporation of mevalonate-2- 14 C into mono- and coupled with mevalonate-2- 14 C feeding, produces results similar to the co-administration of sucrose. The addition of unlabeled sodium acetate slightly increases incorporation of mevalonate-2- 14 C into mono- and sesqui-terpenes, probably by 'sparing' mevalonate rather than by satisfying an energy requirement.