Occurrence and distribution of unsubstituted B-ring flavanones in Eucalyptus foliage

• Published in: Phytochemistry (Oxford) Vol. 160; pp. 31 - 39
• Main Authors: Marsh, Karen J., Saraf, Isha, Hocart, Charles H., Youngentob, Kara, Singh, Inder-Pal, Foley, William J.
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.04.2019
• Subjects: Eucalyptus spp; Herbivory; Monocalypts; Myrtaceae; Near-infrared reflectance spectroscopy; Plant secondary metabolites; Unsubstituted B-Ring flavanones; Plant secondary metabolites; Unsubstituted B-Ring flavanones; Monocalypts; Myrtaceae; Eucalyptus spp; Herbivory; Near-infrared reflectance spectroscopy
• ISSN: 0031-9422; 1873-3700
• DOI: 10.1016/j.phytochem.2019.01.005

A group of plant specialised metabolites (PSMs) collectively known as unsubstituted B-ring flavanones (UBFs) have previously been found in the foliage of some species from the genus Eucalyptus L’Hér. (Myrtaceae), specifically from the subgenus Eucalyptus (monocalypts). Captive feeding studies using artificial diets suggest that these compounds may potentially influence the feeding preferences of marsupial folivores, such as koalas. Understanding natural variation in the composition and concentration of UBFs in eucalypt foliage is a first step to deciding whether, through their effects on herbivory, they might have broader effects on ecosystem dynamics. We used ESI-LCMS/MS and HPLC to characterise and quantify UBFs in 351 individual trees from 25 monocalypt species. We found large variation in the total UBF concentration both between and within species. For example, the mean concentration of UBFs in Eucalyptus muelleriana was 0.2 mg g−1 dry wt, whereas it was 105.7 mg g−1 dry wt, with a range of 78.2–141.3 mg g−1 dry wt, in Eucalyptus mediocris. Different eucalypt species contained different subsets of ten UBFs, and three species showed potential chemotypic variation between individuals within species. Our results suggest that UBFs naturally vary between monocalypt species and individuals at concentrations that could realistically be expected to affect the feeding dynamics of marsupial eucalypt folivores. UBFs could be measured relatively rapidly and cheaply in future studies using near-infrared reflectance (NIR) spectroscopy, as we were able to successfully predict the total UBF concentration of samples from their NIR spectra, with an r2 value of 0.98 and a standard error of prediction (SEP) of 6.07. This work further solidifies NIR spectroscopy as a powerful tool enabling ecologists to analyse the chemical composition of large numbers of samples. Leaves from 25 Eucalyptus species contained various combinations and concentrations of unsubstituted B-ring flavanones, which are deterrent to some marsupial folivores. [Display omitted] •Unsubstituted B-ring flavanones (UBFs) were quantified in 24 Eucalyptus species.•Total UBF concentrations varied between eucalypt trees and species.•UBFs in many trees occurred at concentrations known to deter herbivory.•Many species contained different subsets of UBFs.•Near-infrared spectroscopy was a good alternative method to analyse UBFs.