Polymorphism in cyanogenic glycoside content and cyanogenic β-glucosidase activity in natural populations of Eucalyptus cladocalyx

Abstract

Cyanogenesis is the process by which plantsrelease hydrogen cyanide (HCN) from endogenous cyanide-containing compoundsand is thought to play a role in plant defence against generalist herbivores.Cyanogenesis is poorly understood in natural populations, and has been littlestudied in tree species. In this paper we present the first systematic surveyof cyanogenesis in the economically and ecologically important genusEucalyptus. We document variability in both theconcentration of the cyanogenic glycoside, prunasin, and the accompanyingdegradative b-glucosidase in a woody plant for the first time. Leaves of 96E. cladocalyx F. Muell. trees growing in naturalpopulations on Kangaroo Island, South Australia were analysed. All trees werecyanogenic, containing both cyanogenic glycosides and active b-glucosidase.Cyanogenic glycoside concentration varied by over two orders of magnitude. Theb-glucosidase activity varied widely as well, but plants high in cyanogenicglycosides did not necessarily have higher enzyme activity. A significantproportion of the variation in cyanogenic glycoside concentration can beaccounted for by the variation in leaf nitrogen. Most of the variation,however, appears to be the result of genetic polymorphism, which is inheritedindependently of the level of activity of the degradativeb-glucosidase.