Triterpenoids in epicuticular waxes of Dudleya species

The pentacyclic triterpenoids, β-amyrin acetate and taraxerone, are major components in the epicuticular wax of the genus Dudleya.     

Hydrocarbons from epicuticular waxes of Citrus peels

The hydrocarbon fraction of the epicuticular wax layer of peel from 5 cultivars of Citrus was monitored at various stages of fruit development. GLC     

Micromorphology of epicuticular waxes in Centrosperms

Epidermal surfaces of about 500 species from some 250 genera of centrospermous families plus some possibly related families were examined by scanning electron microscopy. The micromorphology of their epicuticular waxes is described under taxonomic aspects. In general, Centrosperms tend to develop wax platelets on their cuticle. Shape and size of these platelets are highly diverse, but specific for some taxa. Particular forms of rodlets and thick wax plates occur only in few taxa. The systematic and taxonomic applicability of wax micromorphology is limited, but tentatively family characterizations are given. The data presented provide additional information concerning the familiar and suprafamiliar classification ofCaryophyllales. Dedicated to the enthusiast of succulent Centrosperms, Prof. DrK. E. Wohlfarth-Bottermann (Director of the Institute of Cytology and Micromorphology, University of Bonn) on the occasion of his 65th birthday in May 1988.     

Influence of leaf epicuticular waxes from cerrado species on substrate selection byAtta sexdens rubropilosa

The influence of leaf epicuticular waxes of nine woody species from cerrado (a savanna ecosystem of Brazil) on the foraging behavior of the leaf-cutting antAtta sexdens rubropilosa Forel, 1908 (Formicidae, Attini) was investigated. Some waxes showed neither inhibitory nor attractive effect over a series of tests, while a second group caused a delayed rejection. Waxes of two species were shown to be strongly deterrent to the ants. Since different waxes caused different responses, it is concluded that their chemical composition, rather than hydrophobicity or mechanical constraints, accounts for the observed effects. Plant species with leaves rejected by the ants did not necessarily have repellent waxes. On the other hand, no species with acceptable leaves yielded waxes with deterrent effects.     

Movement and regeneration of epicuticular waxes through plant cuticles

Regeneration of plant epicuticular waxes was studied in 24 plant species by high-resolution scanning electron microscopy. According to their regeneration behaviour, four groups could be distinguished: (i) regeneration occurs at all stages of development; (ii) regeneration occurs only during leaf expansion; (iii) regeneration occurs only in fully developed leaves; (iv) plants were not able to regenerate wax. Wax was removed from the leaves with water-based glue and a liquid polymer, i.e. water-based polyurethane dispersion. In young leaves these coverings could not be removed without damaging the leaves. After a few days, waxes appeared on the surface of these polymer films, which still adhered to the leaves. It is concluded that waxes move through the cuticle in a process similar to steam distillation. This hypothesis could be further substantiated in refined in vitro experiments. Wax isolated from Eucalyptus globulus was applied to a filter paper, subsequently covered with a liquid polymer and fixed onto a diffusion chamber filled with water. The diffusion chamber was put into a desiccator. After 8-10 days at room temperature, crystals similar in dimensions and shape to in situ crystals appeared on the surface of the polyurethane film. This indicates that waxes in molecular dimensions move together with the water vapor that permeates through the polymer membrane. Based on these results, we propose a new and simple hypothesis for the mechanism of wax movement: the molecules that finally form the epicuticular wax crystals are moved in the cuticular water current.     

Crystallinity of plant epicuticular waxes: electron and X-ray diffraction studies

The crystal structure of the epicuticular waxes of 35 plant species has been examined by electron diffraction and X-ray powder diffraction. The waxes include the most common morphological wax types such as platelets, tubules, films and rodlets. Most of them were prepared with a special mechanical isolation method, which preserves the original crystal structure. Solvent-extracted recrystallized plant waxes were compared with mechanically isolated samples. The waxes were found to occur in three different crystal structures. Most of the waxes exhibited an orthorhombic structure which is the most common for aliphatic compounds. Tubules containing mainly secondary alcohols showed diffraction reflections of a triclinic phase; broad reflection peaks indicated a significant disorder. Ketones, in particular beta-diketone tubules, displayed the reflections of a hexagonal structure. Mixtures of different phases could be identified. For most of the waxes, the 'long spacing' diffraction reflections indicated a layer structure with the characteristics of the major component. Others showed no 'long spacing' reflections indicating a strong disorder of the molecular layers.     

Dependence of the hydrocarbon constituents of the leaf waxes of Khaya species on leaf age

The hydrocarbon constituents of the leaf waxes of eight species of Khaya were analysed for taxonomic purposes using GLC. The leaf waxes contained neither isoalkanes nor alkanes and the bulk of the n-alkanes were in the range of C₂₅ to C₃₃, odd-carbon number compounds predominating. It was found that the percentage composition of the n-alkane constituents of the leaf waxes varied with the age of leaves, young leaves having n-C₂₉ as the most abundant alkane, whereas older leaves had n- C₃₁.     

Influence of epicuticular waxes from white spruce and balsam fir on feeding behavior of the eastern spruce budworm

Fourth-instar larvae of the eastern spruce bud-worm Choristoneura fumiferanaClem. (Lepidoptera: Tortricidae) were shown in two-choice feeding tests to respond differently to epicuticular waxes from different white spruce and balsam fir trees. Larvae also showed different preferences for various wax fractions obtained by separation on silicic acid.Deceased.     

SEM analysis of leaf epicuticular waxes of Sedum section Gormania (Crassulaceae)

Epicuticular leaf waxes in the 12 taxa classified inSedum, sect.Gormania show variation in size, shape, and frequency. All of the taxa exhibit wax platelets, but the platelets in the three putative relicts (S. albomarginatum, S. moranii, S. oblanceolatum) are larger than those in related taxa, and those inS. paradisum are poorly developed. Interspecific hybrids tend to show wax patterns intermediate between those of their respective parents. Hypothetical hybrid origins for the four polyploid taxa in the section have been supported previously by morphological and reproductive data and are further clarified by leaf wax data.     

Antifungal activity of essential oils of Croton species from the Brazilian Caatinga biome

Aims: To find new antifungal agents among essential oils from Brazilian Croton species. Methods and Results: Plant leaves were steam distilled and the obtained essential oils were analyzed by gas chromatography/mass spectroscopy. The main constituents were estragole and anethole for Croton zehntneri, methyl-eugenol and bicyclogermacrene for Croton nepetaefolius and spathulenol and bicyclogermacrene for Croton argyrophylloides. The antifungal activity of essential oils was evaluated against Candida albicans, Candida tropicalis and Microsporum canis by the agar-well diffusion method and the minimum inhibitory concentration (MIC) by the broth microdilution method. Essential oils of Croton species demonstrated better activity against M. canis. Among the three plants C. argyrophylloides showed the best results, with MIC ranging from 9 to 19 μg ml⁻¹. The acute administration of the essential oil up to 3 g kg⁻¹ by the oral route to mice was devoid of overt toxicity. Conclusions: The studied essential oils are active in vitro against the dermatophyte M. canis and present relative lack of acute toxicity in vivo. Significance and Impact of the Study: Because of its antifungal activity and low toxicity, the essential oils of studied Croton species are promising sources for new phytotherapeutic agents to treat dermatophytosis.     

New Passalora species on Peixotoa (Malpighiaceae) from the Brazilian Cerrado

Four new Passalora species were found on leaves of Cerrado native plants of the genus Peixotoa (Malpighiaceae). Two of the new Passalora species (P. peixotae-reticulatae and P. cerradensis) belong in Section Mycovellosiella, while P. peixotoae-goianae and P.brasilianensis belong in Section Phaeoramularia.     

Effect of epicuticular waxes of poplar hybrids on the aphid Chaitophorus leucomelas (Hemiptera: Aphididae)

Abstract:  Insect response to plant surface features is a critical step in host-finding and acceptance of herbivorous insects. The plant surface is usually covered with epicuticular waxes (EWs), which are not only involved in water physiology, but also provide resistance to insects. In the present work the probing behaviour and performance of the aphid Chaitophorus leucomelas Koch (Hemiptera: Aphididae) on dewaxed and waxed leaves of two poplar hybrids, [( Populus trichocarpa Torr. & Gray ×  Populus deltoides Bartram ex Marshall) ×  P. deltoides ] (TD × D) and [( P. trichocarpa  ×  Populus maximowiczii Henry) × ( P. trichocarpa  ×  P. maximowiczii )] (TM × TM), previously reported as susceptible and resistant, respectively, are described. Laboratory experiments showed that in naturally waxed leaves of the resistant hybrids, aphids devoted less time to probing and more time to non-probing behaviour when compared with their behaviour on susceptible hybrids. These differences were not present when leaves of these hybrids were experimentally dewaxed. A field experiment demonstrated that aphid reproductive performance was affected by hybrid genotype (higher in the TD × D) but not by EWs, although a trend of lower performance on dewaxed leaves in both hybrids was apparent. SEM analysis of EWs revealed micromorphological differences between both hybrids. These results support the idea that EWs affect aphid behaviour in poplars, with a rather slight impact on reproductive performance.     

Three new species of Croton (Euphorbiaceae s.s.) from the Brazilian Caatinga

While conducting a floristic inventory of Croton from the Brazilian Caatinga, three new species were discovered. Croton arenosus, Croton glandulosobracteatus, and Croton harleyi are described and illustrated here. Based on morphological characters, Croton glandulosobracteatus is proposed to belong to section Barhamia, and C. arenosus and C. harleyi to section Geiseleria.     

Oriented arrays of epicuticular wax plates inEucalyptus species

Summary Patterns of arrangement of epicuticular wax platelets are shown in a number of species ofEucalytpus. In some, wax platelets are oriented across the long axes of epidermal cells overlying veins and, in some species, over cells of adjacent stomatal complexes. Among other patterns, radial arrangements around stomata, arrangements in lines at right angles to underlying cell walls and concentric arrays are described. The possibility of the involvement of ectodesmata (ectocythodes) in the location of wax platelets is raised. The pattern of orientation of the platelets is ascribed to a prepattern, as yet unobserved, of anisotropic domains in the outer cuticle. It is suggested that this prepattern may consist of regions of molecular anisotropy possibly produced in response to stretching of the cuticle during expansion growth. Wax platelet patterns appear to be restricted to certain taxonomic entities; thus, genetical determinants are also involved in their formation.     

Short-distance pollen dispersal in a protogynous Annonaceae tree species from the Brazilian Cerrado

Annona crassiflora (Annonaceae) is a protogynous beetle-pollinated savannah tree species, widely distributed in the savannahs of the Cerrado biome. Studies on the mating system and pollen dispersal of protogynous species are very scarce. Here, we used six microsatellite loci to assess the mating system and pollen dispersal of A. crassiflora in a savannah remnant in Central Brazil. We mapped and sampled leaves of 112 adult trees and collected 74 fruits from 20 mother trees (1–4 fruits per plant) to obtain the seeds used (460) for mating system and parentage analyses. Annona crassiflora has predominantly allogamous mating systems, with a high multilocus outcrossing rate (t_m?=?0.974, SE?=?0.011) that did not differ among mother trees (F?=?1.32, p?=?0.165). However, t_m–t_s was variable among seed trees, indicating that some seeds were produced by mating among relatives. Our results also showed multiple paternity within fruits. Multilocus correlation of outcrossed paternity was high (r_p?=?0.302, SE?=?0.045), indicating that for each mother tree, the probability that the same pollen donor sired two random sibs was 30.2%, and the mean number of pollen donors per mother tree was high (6.3). We detected a maximum pollen dispersal distance of 360.7 m and an average of 124.3 m (SD?=?80 m), but most pollination events (73%) occurred at shorter distances (<?160 m), indicating short-distance pollen dispersal, most likely due to the pollinator behaviour.     

FTIR spectroscopy of synthesized racemic nonacosan-10-ol: a model compound for plant epicuticular waxes

As there are no published graphically presented, detailed IR spectra of nonacosan-10-ol (occurring naturally and widely in plant epicuticular waxes of nanotube form), near IR FTIR spectroscopy (fundamentals, overtones and combinations) has been performed on laboratory synthesized racemic nonacosan-10-ol, as a crystalline solid on Mylar and polypropylene substrates. Room temperature, in vacuo data are presented graphically, in full, and show evidence of extensive hydrogen bonding, an orthorhombic perpendicular subcell, a methylene wagging progression, diagnostic of all-trans conformational order, and Fermi resonance. Moderate or stronger anharmonicity is confirmed. Detailed discussion, quantitative in parts, is given of the observed spectral features, especially as to how they inform crystal structure and molecular conformation, and assignments given for some of the features. The results will serve as a reference for future IR studies of the natural epicuticular wax nanotube form of (S)-nonacosan-10-ol.     

Epidermal conductance in different parts of durum wheat grown under Mediterranean conditions: the role of epicuticular waxes and stomata

Abstract. Epidermal (non-stomatally-controlled) conductance from the fourth leaf, first node leaf, flag leaf and ear of durum wheat (Triticum turgidum var durum L.) grown under Mediterranean field conditions has been measured, along with leaf stomatal frequency and the amount and distribution of epicuticular waxes. Measurements were carried out on varieties and land-races from the Middle East, North Africa, ‘Institut National de la Recherche Agricole’ (INRA) and ‘Centra Internacional de Mejora de Maiz y Trigo’ (CIMMYT). Significant differences were observed among genotypes in the epidermal conductances (g_e) of the four organs. For each of the four organs tested, genotypes from the Middle East and CIMMYT showed higher g_e. values than those from North Africa and INRA. Ears showed epidermal conductances that were more than four times higher than those of leaves when g_e. values were expressed per unit dry weight. The amount of epicuticular waxes was higher in the fourth leaves, intermediate in the first node and flag leaves and lower in the ears. For each organ, g_e differences among genotypes were unrelated with the amount of epicuticular waxes. Removal of epicuticular waxes by dipping the organs into chloroform significantly increased the epidermal conductance for the fourth and first node leaves and the ear. However, this did not occur for the flag leaf. For the fourth leaf, g_e of intact leaves and g_e of leaves in which epicuticular waxes were removed were unrelated (r = -0.265). The regression coefficient of this relation for the first node and flag leaves showed values of 0.666 and 0.650 (P > 0.05), respectively, and values were even higher in the ear (r > m 0.892, P > 0.01). Scanning electron microscope analysis showed that wax bloom decreased from the fourth leaf to the flag leaf, whereas the extent of amorphous wax increased. Wax bloom in leaves consisted mainly of deposits of thin wax plates. In the ears and the adaxial surface of flag leaves, fibrillar waxes predominated. In the first node and flag leaves, the wax deposits on the adaxial side cover the surface of the leaf more densely and uniformly than those on the abaxial side. There was no significant correlation between g_e and total stomatal density, or between g_e and either adaxial or abaxial stomatal density for any sample of the three different leaves. The contribution of epicuticular waxes plus total stomatal frequency only explained 42.4, 11.8, 28.3 and 16% of g_e (per unit leaf area) variations for the fourth leaf, first node leaf, flag leaf and the combined variation of the three leaves together, respectively. From these results, it is concluded that complex interrelationship between different morphophysiological characteristics probably control g_e differences among genotypes and that these interrelationships differ for each different plant part.