Foliar Wax Research Articles

Morphology and Accumulation of Epicuticular Wax on Needles of Douglas-fir (Pseudotsuga menziesiivar.menziesii)

Abstract Past studies have documented differences in epicuticular wax among several tree species but little attention has been paid to changes in accumulation of foliar wax that can occur during the year. We sampled current-year needles from the terminal shoots of Douglas-fir (Pseudotsuga menziesii var. menziesii) in late June/early July, late August and early November. Needles were sampled from two sites that differed in their climate and shoot phenology. Adaxial (upper), abaxial (lower) and cross-sectional surfaces were examined on scanning electron micrographs. Wax thickness increased significantly (P < 0.01) during the year (from 2.9 ± 0.26 µm in late June/early July to 4.4 ±0.13 µm in early November). Mean wax thickness was slightly thicker on adaxial (4.0 ± 0.16 µm) than on abaxial (3.5 ± 0.22 µm) surfaces (P = 0.03). There were no significant differences in wax thickness between needles sampled at the base of the terminal shoot or near the tip of the shoot. Tubular or rod-shaped epicuticular wax cr...

Foliar cuticular waxes of cultivated species and varieties of Coffea

Abstract The cuticular waxes of leaves of Coffea arabica cv. ‘Catuai Vermelho’, C. arabica cv. ‘Obata’, Coffea canephora cv. ‘Apoata’, Coffea racemosa and two hybrids between C. arabica and C. racemosa were extracted by rapid washing of the surface with chloroform. The waxes were fractionated by thin layer chromatography over silicagel. The fractions of the constituent classes were characterized by infrared spectroscopy and the distribution of the homologs of the n -alkanes and n -primary alcohols was determined by GC/MS and GC/FID. Among the samples analyzed, leaves of C. racemosa have the highest content of foliar wax (22.9 μg cm −2 ). Most samples contain either n -alkanes ( C. canephora and C. racemosa ) or n -primary alcohols ( C. arabica ) as predominant wax constituents. The distribution of n -alkanes allowed the distinction of C. racemosa from the other samples; the distribution of alcohols allowed the distinction of the three species. The two hybrids have waxes similar to the wax of C. arabica .

Cera total e perfi l dos p-alcanos de frutos e folhas de Ocnrkijkc"incdtc"L.

Malpighia glabra L., popularly known as acerola or Barbados cherry, is an economically important species due the high levels of ascorbic acid (vitamin C) in its fruits. Cuticular wax affects post-harvest storage. Nevertheless, no data are available for wax composition on this species. Crude wax amount and n-alkane profiles have been evaluated for three distinct genotypes of acerola. The total amount of wax ranged from 11 µg.cm-2 to 24 µg.cm-2 on leaves and 10 µg.cm-2 to 30 µg.cm-2 on fruits. Two of the three genotypes presented statistically distinct totals for leaf and fruit-wax. Type A (yellow epicarp) presented the highest amounts of crude wax on both leaves and fruits. n-Alkanes ranged from C18 to C34 in fruits, with n-pentacosane (C25) as the main homologue of most individuals. Narrower n-alkane distribution was found in cuticular foliar wax, with C22-C33, with n-hentriacontane (C31) as the major component of most individuals. The environmental and economical aspects related to total wax amounts and n-alkane profiles are discussed herein.

Constitutive or induced defences - how does Eucalyptus globulus defend itself from larval feeding?

Following herbivory, induced responses involving plant secondary metabolites have been reported in a number of tree species. Although a wide range of plant secondary metabolites appear to operate as constitutive plant defences in trees belonging to the Eucalyptus genus, no induced responses have as yet been reported following foliar-chewing insect damage. We empirically tested whether branch defoliation (artificial and larval) of 2-yearold Eucalyptus globulus Labill. trees altered the abundance of specific plant secondary metabolites immediately (3 months after initial larval feeding) and 8 months after the cessation of larval feeding. Metabolites assayed, included essential oils, polyphenolic groups and foliar wax compounds and in all cases their abundance was not significantly altered by defoliation. However, the level of foliar tannins after 3 months of larval feeding did display a trend that suggested elevated levels as the result of defoliation, though this trend was not evident 8 months later, indicating that, if real, the response was a rapid and not a delayed induced response. The level of foliar tannins was also negatively correlated to both average larval survival and average percentage branch defoliation, suggesting that foliar tannins may operate as toxins and/or anti-feedants to M. privata larval feeding.

Susceptibility of Eucalyptus globulus to Mnesampela privata defoliation in relation to a specific foliar wax compound

Increased abundance of several aliphatic benzyl and phenylethyl alkanoates were previously associated with reduced defoliation of Eucalyptus globulus Labill. by the autumn gum moth (Mnesampela privata Guenee) in two clonally replicated F2 families. We examine the robustness of this association by comparing the abundance of the implicated foliar wax compounds with defoliation levels in three plantation sites and a genetics trial in northern Tasmania. At all locations, the aliphatic alkanoate, benzyl n-tetracosanoate (C24), was found in significantly higher abundance in the foliar wax of E. globulus trees that had displayed low M. privata damage (designated resistant) compared to trees that had displayed high damage (designated susceptible). Further, when sites were combined, benzyl n-tetracosanoate (C24) accounted for 16 % of variation in field defoliation. Field defoliation was also positively correlated to M. privata oviposition both in the field and on foliage sprigs in a cage. In the cage bioassay, oviposition accounted for 20 % of variation in field defoliation making it a better predictor of tree defoliation in the field than either field oviposition, which accounted for 9 % of variation, or screening foliage for the abundance of benzyl n-tetracosanoate (C24). Despite both benzyl n-tetracosanoate (C24) and oviposition being related to field defoliation, there was no statistically significant relationship between the abundance of benzyl n-tetracosanoate (C24) and oviposition in the field or cage bioassay. Further work is therefore required to determine if increased levels of this compound in the foliar wax operates as a direct deterrent to M. privataoviposition.

Distribution and evolution of secondary metabolites in Eriocaulaceae, Lythraceae and Velloziaceae from "campos rupestres"

Hypotheses are presented on the evolution of structural patterns of secondary metabolites (flavonoids and foliar wax alkanes) and fatty acids of families of "campos rupestres". The distribution of fatty acids is given for genera of Lythraceae, with emphasis on Cuphea (supposedly more advanced) and Diplusodon. Compounds with saturated short chains represent a derived condition in Lythraceae although they are probably restricted to Cuphea. It is suggested that evolution selected for more complex flavonoid patterns in Cuphea, with the inclusion of C-glycoflavones and methoxylated flavonols (rhamnetin and isorhamnetin), which are not found in members of Diplusodon and Lafoensia. The supposedly primitive groups of Eriocaulaceae (e.g., Paepalanthus) presented more complex flavonoid patterns characterized by flavones and flavonols, the latter frequently being 6-hydroxylated or methoxylated. More advanced groups of Eriocaulaceae (e.g., Leiothrix and Syngonanthus) apparently possess only flavones, C-glycoflavones are a salient feature of species with smaller habits. In Velloziaceae, members of the primitive subfamily Vellozioideae show distribution of alkanes of foliar epicuticular wax in which C27, C29 or C31 predominate; members of the derived subfamily Barbacenioideae usually show distributions with a predominance of C33 or C35, while species of Pleurostima (Barbacenioideae) have C31 as the main homologue, thus being intermediate between the two subfamilies. It is suggested that the evolution of alkanes in Velloziaceae follows a trend toward elongation of carbon chains. The condition of advanced or primitive chemical patterns is inferred from the results of cladistic analyses based on morphological characters (Eriocaulaceae and Lythraceae), and morphological and molecular characters (Velloziaceae).

Evolutionary diversity among Atlantic coast mangroves

Current knowledge of intraspecific variation of mangrove species is limited in terms of rangewide distributions and is mostly restricted to morphological analyses, which have indicated a high degree of homogeneity. However, our analyses of the aliphatic hydrocarbon and triterpenoid fraction of foliar waxes (by gas chromatography and mass spectroscopy) of mangrove species ( Rhizophora mangle, Avicennia germinans and Laguncularia racemosa ) from Gabon in West Africa and French Guiana in South America show significant genetic differentiation between eastern and western Atlantic provenances. The greater diversity in lipid composition, and the tendency for longer carbon chain lengths in all taxa from Africa, may suggest that American mangroves exhibit derived characteristics. A consequence of this hypothesis would be that Atlantic mangroves are unlikely to have dispersed from the Tethys via the Pacific, as has been proposed by some authors. More widespread sampling within the Atlantic and east Pacific region is needed to support and confirm these results.

Effect of constituents of the foliar wax of Didymopanax vinosum on the foraging activity of the leaf‐cutting ant Atta sexdens rubropilosa

AbstractLeaf epicuticular waxes may affect substrate selection by leaf‐cutting ants, and host recognition by several phytophagous insects. The influence of the crude epicuticular wax of Didymopanax vinosum E. March. (Araliaceae), and its major constituents lupeol and free primary alcohols, on substrate selection by the leaf‐cutting ant Atta sexdens rubropilosa Forel, was investigated. Two ant colonies were used in laboratory bioassays. Corn flakes (zea) were impregnated with chloroform solutions of the substances being tested and fed to the adults. One of the colonies gave results, in most of the tests, not significantly different from the controls. The other colony, however, discriminated against the crude wax, a strong deterrent effect being observed from the first of a series of eight trials. The same colony was able to discriminate against lupeol after the second trial. The fraction of primary n‐alcohols (22% C28, 66% C30 and 12% C32) deterred feeding only after the fifth trial. The results demonstrate that some constituents of epicuticular waxes may deter the foraging activity of A. sexdens rubropilosa, depending, however, on the colony under observation. It is suggested that lupeol, of the foliar wax of D. vinosum, is an important deterrent to leaf‐cutting ants, although with less pronounced effects than those observed in tests with the crude wax.

Biogeographic variation in foliar waxes of mangrove species

Foliar epicuticular wax composition of mangrove species with natural distributions in West Africa and the Atlantic coast of South America, was studied by GC in order to investigate possible biogeographic variation. South American (Guyana) populations of Avicennia germinans were very much poorer in triterpenoids and in C 32 alkane and richer in C 28 alkane than populations from West Africa (Gabon). Shrub forms of A. germinans were richer in triterpenoids than trees. Dwarf forms of Conocarpus erectus were much poorer in triterpenoids, than shrub forms of this species. The pattern of alkane composition in Rhizophora from Guyana was unimodal, with unusually high amounts of C 28, contrasting with a bimodal pattern, with modes at C 28-C 29 and C 31, in Rhizophora from Gabon. Foliar wax of Laguncularia racemosa from Guyana contained only trace amounts of triterpenoids and a broad range of alkanes with modes at C 29 and C 33, whereas triterpenoids were present in significant amounts and most of the alkane fraction consisted of C 27 - C 29 in Gabon. These preliminary data suggest significant biogeographic variation within these taxa.

Initial deposits and persistence of azadirachtin in fir and oak foliage after spray application of ‘Margosan‐O’® formulation

AbstractFoliar deposits and persistence of azadirachtin were investigated after spraying ‘Margosan‐O’® formulation at three dosage and volume rates on to balsam fir and oak seedlings in a laboratory chamber. Droplet‐size spectra and deposits were assessed using artificial samplers, and foliar residues were measured by high‐performance liquid chromatography (HPLC) at different intervals of time after treatment. Disappearance of azadirachtin from both types of foliage was rapid, and the DT50 (the time required for 50% of the initial concentration to disappear) values ranged from 17 to 22 h. The initial azadirachtin concentrations varied widely from 4 to 96 μg g−1 (fresh weight), but the rate constants 0.0311 to 0.0414, were not significantly different. The data thus indicated a poor relationship between initial concentrations and the rate of loss.The influence of spray droplet size and cuticular wax content of foliage on persistence of azadirachtin was investigated using both foliar types, and glass microscope slides without and with the foliar wax coating. Neither the type of surface nor the droplet size influenced the persistence. The rate of azadirachtin loss from the glass slides was faster than from both types of foliage, and was unaffected by the presence of wax coating. The fir foliage had higher cuticular wax content than the oak foliage, but the persistance of azadirachtin was similar in both foliar types.

Foliar chemicals of wheat and related grasses influencing oviposition by Hessian fly,Mayetiola destructor (Say) (Diptera: Cecidomyiidae)

More than twice the number of mated female Hessian flies,Mayetiola destructor (Say) entered a zone within 1 cm of a paper strip treated with one plant equivalent (PE) of a chloroform extract of wheat foliar waxes compared to a strip treated with solvent only; females also stayed six times longer and laid 10 times more eggs on the strip treated with the wheat extract. Column chromatographic fractionation of the wheat extract and application of these fractions onto filter paper strips showed four fractions elicited significant numbers of eggs to be laid. Single, binary, and tertiary combinations of three of these fractions (two of the four fractions apparently contained similar compounds) were tested. The greatest numbers of eggs were laid on strips treated with the tertiary combination or the binary combination conaining the two most active fractions (3 and 6); three times the number of eggs were laid on strips treated with this binary combination than the sum of eggs laid on strips treated with these two fractions separately. A comparison of grasses and their extracts showed female Hessian flies laid greater numbers of eggs on wheat or rye than on barley or oat. Fractionated barley and oat extracts were tested for activity as for wheat, and a similar pattern was observed, i.e., the greatest numbers of eggs were laid on fractions 3 and 6. Dose-response tests, using these two fractions of wheat, barley, or oat showed the same threshold of activity for fraction 3 for all three extracts, i.e., 2 PE. In contrast, fraction 6 of wheat was active at the lowest dosage tested, 0.25 PE, while the same fraction of either barley or oat was not active until tested at a dosage of 2 PE. It appears that (at least) two chemicals in the foliar waxes of these grasses influence ovipositional behavior of female Hessian flies. Furthermore, given the similar foliar chemistry of these grasses and the strong synergistic interaction between fractions 3 and 6 shown for wheat extract, it is likely that the ovipositional preferences exhibited by female Hessian flies towards these grasses may be explained by quantitative differences in the amount(s) of the active chemical(s) in their respective fraction 6 (most polar fraction tested).

Alkanes of surface waxes from eight species of aquatic angiosperms

Surface waxes from eight species of aquatic angiosperms were extracted. Four species have submerged leaves ( Cabomba caroliniana Gray, Egeria densa Planch., Eriocaulon aquatile Koern. and Mayaca fluviatilis Aubl.), three have emergent leaves ( Eichhornia crassipes (Mart.) Solms, Myriophyllum aquaticum (Vell.) Verdc. and Pistia stratiotes L.) and one has floating leaves ( Nymphaea mexicana Zucc.). In all cases the yield of waxes was low and ranged among the species from 1.1 to 16.1 μg cm −2. The alkanes were separated from the waxes through column chromatography and identified by means of gas chromatography. The carbon chains of the alkanes of the species with submerged leaves are, on average, shorter than those of the species with air-exposed leaves. The distribution of alkanes of the latter species is similar to the alkane profiles of foliar waxes of terrestrial plants.

The Effect of Day and Night Temperature on Growth, Foliar Wax Content, and Cuticle Development of Velvet Mesquite

The Effect of Day and Night Temperature on Growth, Foliar Wax Content, and Cuticle Development of Velvet Mesquite