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Mosaic trees contain more than one phenotype. The two Eucalyptus mosaic trees studied here (E. melliodora and E. sideroxylon) are predominantly susceptible to insect herbivory, with the leaves on a single large branch on each tree resisting herbivory. We used gas chromatography-mass spectrometry and high-pressure liquid chromatography to analyze the chemical profile of leaves of the mosaic trees, as well as leaves of adjacent non-mosaic con-specifics. We show that the leaves of the two phenotypes are distinctly different. Compared to the susceptible (S) leaves on the same tree, the resistant (R) leaves on the mosaic trees had low concentrations of sesquiterpenes (E. melliodora: 2 vs. 24 mg·g(-1) dry matter; E. sideroxylon: 8 vs. 22 mg·g(-1) dry matter), high concentrations of FPCs (E. melliodora: 5.4 vs. 0.3 mg·g(-1) dry matter; E. sideroxylon: 9.8 vs. 0.2 mg·g(-1) dry matter) but similar concentrations of nitrogen (E. melliodora: 15.4 vs. 16.8 mg·g(-1) dry matter; E. sideroxylon: 13.1 vs. 14.0 mg·g(-1) dry matter). The only difference between the two mosaic trees was in the levels of monoterpenes. The R leaves from the mosaic E. melliodora contained higher concentrations of monoterpenes compared to the S leaves (12 vs. 6 mg·g(-1) dry matter). In contrast, the leaves from the E. sideroxylon mosaic contained much higher concentrations of monoterpenes with a reversed pattern (R: 26 vs. S: 45 mg·g(-1) dry matter). There were qualitative differences too on the mosaic trees. The R leaves of both species contained much higher concentrations of the monoterpene, 1,8-cineole, whereas the S chemotype of E. sideroxylon only had high concentrations of phellandrenes. Furthermore, the chemical differences between leaves on the R and S branches of the mosaic trees resembled those between the leaves of R and S con-specific trees in the same population. We use these data and knowledge of secondary metabolite biosynthesis to propose that high-level transcriptional differences may control the profile of specialized metabolites in eucalypts.

The variation of foliar monoterpenes in the Australian Tea Tree (Melaleuca alternifolia) has been of significant interest both to the essential oil industry as well as to ecologists. The majority of studies on leaf chemistry have been aimed directly towards obtaining oil of higher quality or quantity. In the current study, we aimed to understand how molecular mechanisms contribute to the chemical variability of this species, based on chemical analysis of the leaf oils from a biochemical perspective. Correlations between monoterpenes across the species as well as within chemotypes show strong, persistent patterns, which enable us to establish groups based on possible common biosynthetic origins. We found that three distinct enzymes corresponding to these groups: a sabinene-hydrate synthase, a 1,8-cineole synthase, and a terpinolene synthase may be sufficient to explain all six chemotypes in M. alternifolia.