Epicuticular waxes and plant primary metabolites on the surfaces of juvenile Eucalyptus globulus and E. nitens (Myrtaceae) leaves

OurknowledgeofthecompositionofthewaxesonthesurfacesofEucalyptusleavesisgrowingbutthatofplant primarymetaboliteshasbeencompletelyoverlooked.Thediffusionofprimarymetabolitesabovethecuticleexposesthemto avarietyofherbivoroustaxaandhasthepotentialtoinfluencetheirresponsestothatplant.Juvenileleavesoftwofamiliesof Eucalyptus globulus Labill. ssp. globulus and two families of E. nitens (Deane & Maiden) Maiden had 11 out of 16 of the epicuticularwaxesthatweredetectedincommon.However,twophenylethylesters(waxes)wereonlydetectedonleavesof one family of E. globulus and two benzyl esters (waxes) were not detected or were uncommon in samples from E. nitens. Wax compounds were generally found in samples from both leaf surfaces but a few were only detected in samples from particularsides.Speciesandfamiliesofeucalyptdidnotdiffersignificantlyintheconcentrationsoffreesugars,polyols,malic acid or g-aminobutyric acid (GABA) (all plant primary metabolites) collected from the surfaces of leaves. However, concentrations of all these metabolites were usually higher in collections from the upper surfaces of leaves. High wax abundance, especially on the lower surfaces of E. globulus leaves, is suspected to have hindered dissolution of all the primary metabolites quantified. Several free amino acids exhibited significant species-level differences in concentrations, namely the aromatic, amide and sulfur-containing amino acids as well as proline; family-level differences in amino acid concentrations were not significant. Australian and overseas evidence showing that differences in waxes and primary metabolitescanbeinfluentialinplantsusceptibilitytoherbivoroustaxaisconsideredwithrespecttothethreatsposedbythe autumn gum moth and Mycosphaerella leaf spot fungi.