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

Abstract

Abstract. Our knowledge of the composition of the waxes on the surfaces of Eucalyptus leaves is growing but that of plant primary metabolites has been completely overlooked. The diffusion of primary metabolites above the cuticle exposes them to a variety of herbivorous taxa and has the potential to influence their responses to that plant. Juvenile leaves of two families of Eucalyptus globulus Labill. ssp. globulus and two families of E. nitens (Deane & Maiden) Maiden had 11 out of 16 of the epicuticular waxes that were detected in common. However, two phenylethyl esters (waxes) were only detected on leaves of 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 particular sides. Species and families of eucalypt did not differ significantly in the concentrations of free sugars, 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 metabolites can be influential in plant susceptibility to herbivorous taxa is considered with respect to the threats posed by the autumn gum moth and Mycosphaerella leaf spot fungi.

Fungal species diversity in juvenile and adult leaves of Eucalyptus globulus from plantations affected by Mycosphaerella leaf disease

“…Other mechanisms of general resistance differing between adult and juvenile leaves like waxes or metabolites present inside leaves or in the cuticle surface could also limit the access of some fungal species to adult tissue (Li et al , 1997; Gras et al , 2005; Steinbauer et al , 2009).…”

Estimation of the solubility parameters of model plant surfaces and agrochemicals: a valuable tool for understanding plant surface interactions

“…Alkanes are also the dominant class of wax compounds extracted from pepper fruits, followed by triterpenoids such as α- or β -amyrin [39-41]. Beta -diketones are the dominant class of wax compounds in juvenile Eucalyptus leaves, but n -nonacosane, heptadecan-2-one and n -hexacosanal are also present in significant concentrations [42-46]. …”

GC-MS Metabolomics to Evaluate the Composition of Plant Cuticular Waxes for Four Triticum aestivum Cultivars

“…The use of GC-MS instrumentation for low molecular weight, volatile compounds such as cuticular waxes is recommended [ 11 , 13 , 24 , 28 , 29 , 30 ]. Gas chromatography apparatuses include a hot evaporation chamber where samples are injected prior to column separation.…”

“…A common method to evaluate primary metabolites in plants is to extract, derivatize via silylation, and detect metabolites using gas chromatography coupled to mass spectrometry (GC-MS) [ 27 ]. Many plant waxes are small and semi-volatile, and are also detected using GC-MS [ 11 , 13 , 24 , 28 , 29 , 30 ]. Further, many contain hydroxyl groups that allow for derivatization to improve volatility and detection by GC-MS.…”