Chemical Composition Of Cuticular Waxes Research Articles

Water permeability of different aerial tissues of carnations is related to cuticular wax composition.

Cuticular wax protects aerial plant tissues against uncontrolled water loss. To compare the differences among tissues, cultivars, and postharvest stages, we characterized the surface morphology, water permeability, and chemical composition of cuticular wax on the leaf, calyx, and petals of two carnation cultivars ('Master' and 'Lady green') at two postharvest stages. Obvious differences in these characteristics were found among tissues but not among cultivars or postharvest stages. The leaf surface was relatively smooth, whereas convex cells were observed on the petals. The mean minimum conductance of leaves was significantly higher than that of the calyx, followed by that of petals. It ranged between 8.8 × 10-4 m s-1 for 'Lady green' leaves at Stage II and 3.6 × 10-5 m s-1 for 'Master' petals at Stage I. Petal wax contained high concentrations of n-alkanes, whereas primary alcohols dominated in leaf wax. The weighted average chain length (ACL) was higher in petal wax than in leaf wax; it ranged from 19.6 in 'Lady green' leaves to 24.14 in 'Lady green' petals at Stage I. In conclusion, carnation petals are characterized by numerous convex cells on both the adaxial and abaxial surfaces, and their main cuticular wax components, alkanes, have a higher ACL than leaf cuticular wax, which contributes to their higher water barrier property. The results provide further evidence for the association between cuticular chemical composition and the physiological function of the cuticle in blocking water transpiration.

Wax-extraction effect on water permeances of three isolated plant cuticles.

The cuticle is a heterogeneous, extracellular biopolymer, which is synthesized by epidermal cells. It plays many physiological and ecological roles but its main function is the reduction of water loss from plants when the stomata are closed. Cuticular waxes are essential part of the cuticle structure and their presence is limitation factor in controlling water permeability. Therefore, knowledge about amounts and chemical composition of cuticular waxes is necessary in order to understand their functions. This study was conducted to find out the effect of wax extraction on water permeability of three isolated plant species cuticles. The cuticles were enzymatically isolated and waxes were extracted from the cuticles using chloroform. The results showed that the water permeance was affected by removing waxes from cuticle structure and it was increased by high factor for all treated plants. This study showed no correlation between wax coverage of each single species and its water permeability

Morphological, chemical, and biosynthetic changes in pericarp waxes in response to the browning of litchi fruit during storage

Litchi fruit is susceptible to pericarp browning after harvest, which is regulated by the oxidation of polyphenols and membrane lipids during storage. Cuticular waxes form the outermost lipid layer covering plant surfaces, and their changes in response to pericarp browning in litchi remain unclear. In this study, changes in morphological appearance and chemical composition of cuticular waxes, and expression of their associated biosynthesis regulatory genes in litchi were comprehensively investigated. In terms of pericarp microstructure, cuticular variations, such as wrinkled lines with “tooth-like” cuticular ridges, appeared on the epidermal cell surface. Following pericarp browning, the protruding nano-ridges were damaged, resulting in a disturbed appearance. Parallel to the appearance of morphological changes, we observed a 2.3-fold increase in cuticular waxes in the browned pericarp when compared with fresh fruit. Concerning chemical compositions, slight changes in the cyclic constituents were observed, whereas the synthesis of very-long-chain fatty acids, primary alcohols, aldehydes, and n-alkanes with carbon chains greater than C26 appeared to be stimulated in the browned pericarp. Correspondingly, similar increased trends were detected in the relative gene expression levels of LcLACS1/2, LcCER2, LcKCR1, LcHACD, and LcECR in fatty acid elongation, LcCER1 in n-alkanes, and LcFAR1 in primary alcohols. These results indicated that changes in surface microstructure modifications and the increase in biosynthesis of cuticular waxes, particularly the very-long-chain aliphatic components, occurred in response to the browning of litchi fruit during storage. Accordingly, surface cuticular waxes might also play an important role in regulating the browning of fruits during storage.

Comparative profiles of the cuticular chemicals and transpiration barrier properties in various organs of Chinese flowering cabbage and Chinese kale.

Plant cuticle as hydrophobic barrier covers almost all aerial plant organs. Herein the cuticular chemical components and the transpiration of various organs of Chinese flowering cabbage (CFC) and Chinese kale (CK) were comprehensively characterized. Numerous species- and organ-specific differences in morphological, chemical, and physiological levels were found. The various organs were relatively smooth in surface for CFC but glaucous with hollow tube- and plate-type crystals for CK. The chemical composition of cuticular waxes were very-long chain n-alkanes, ketones, secondary alcohols with a prominent carbon chain of C29 in CK, primary alcohols dominated by C26 , and aldehydes prominently C30 in CFC. Cutin monomers accumulated with similar levels as waxes and were dominated by α,ω-dicarboxylic acids and fatty acids without added groups. The minimum water conductance differed considerably among species and various organs ranging between 8.9 × 10-5 (CK leaf) and 3.7 × 10-4 m s-1 (CFC leaf petiole). These differences in transpiration properties were proposed to be largely related to the cuticular chemicals in various organs and species. The presented results provide further insights to link the transpiration barrier functions with surface characteristics and cuticular chemicals.

Comparative analysis of cuticular waxes of the gametophyte and sporophyte of three species of Polytrichaceae

Few data are available about cuticular wax of mosses, in general, as well as for Polytrichaceae. In addition, most of these studies investigated only the gametophyte. To improve understanding of wax components and their ecological roles, we compared the morphology and the chemical composition of cuticular waxes of the gametophyte and the sporophyte of the Brazilian species Pogonatum pensilvanicum, Polytrichadelphus pseudopolytrichum (endemic), and Polytrichum juniperinum. The waxes were extracted with dichloromethane, derivatized and analyzed using gas chromatography coupled with mass spectrometry. The total wax content was expressed in µg cm–2 and the compounds were identified based on mass fragmentation patterns. The morphology of epicuticular waxes was studied by scanning electron microscopy. Thicker wax layers were observed over the leafy gametophyte and the calyptra, ranging from 0.2 to 0.3 µg cm–2. For the sporophyte, the wax layer was not homogeneous, ranging from 0.01 to 0.04 µg cm–2 over the seta and from 0.07 to 0.2 µg cm–2 over the capsule. While alkanes and fatty acids were found in the two generations, primary alcohols were detected only in the leaves, and aldehydes and esters were found only in the sporophyte. Nonacosan-10-ol was more abundant in the calyptra and capsule. Film waxes were predominant in the gametophyte and sporophyte. Qualitative and quantitative differences were detected in wax composition according to life phases. As far as we know, this is the first time that the sporophyte parts were investigated separately. We hypothesized that the higher wax content in the calyptra may contribute to the protection of the capsule; however, this idea needs to be confirmed. Besides, our data support previous statements that the biosynthetic machinery for wax components was present in the earliest land plants, protecting both the gametophyte and the sporophyte.

Comparative analysis of the cuticular waxes and related gene expression between ‘Newhall’ and ‘Ganqi 3’ navel orange during long-term cold storage

Previously, we obtained a wax-deficient mutant ‘Ganqi 3’ (MT) from ‘Newhall’ navel orange (Citrus sinensis [L.] Osbeck cv. Newhall, WT). The weight loss and postharvest decay in MT fruit were much higher than those in WT fruit after long-term cold storage. To understand the underlying mechanism, the changes in the morphology, chemical composition and gene expression of cuticular waxes between WT and MT fruit were compared during 150 days of storage at 4 °C. The density of epicuticular wax crystals and the contents of most of the aliphatic wax fractions in MT fruit were much lower than those in WT fruit over 90 days of storage. Further research revealed that the differences in the morphology and chemical composition of cuticular waxes might be important causes for the differences of postharvest weight loss and decay rates between WT and MT fruit. Notably, the expression profiles of 16 wax-related genes in WT and MT fruit were consistent with the change trends of corresponding cuticular wax components during cold storage. These results suggest that the morphology and chemical composition of cuticular waxes may be regulated by wax-related genes and play an important role in regulating the postharvest weight loss and the tolerances to postharvest decay in navel orange.

Physical and Chemical Traits of Grape Varieties Influence Drosophila suzukii Preferences and Performance.

The cuticle-covered surface forms the interface between plant parts, including fruits, and their environment. The physical and chemical properties of fruit surfaces profoundly influence plant-frugivore interactions by shaping the susceptibility and suitability of the host for the attacker. Grapevine (Vitis vinifera, Vitaceae) serves as one of the various host plants of the spotted wing drosophila, Drosophila suzukii Matsumura (Diptera: Drosophilidae), which is invasive in several parts of the world and can cause major crop losses. The susceptibility of wine towards this pest species differs widely among varieties. The objective of our study was to identify physical and chemical traits of the berry surface that may explain the differences in susceptibility of five grape varieties to D. suzukii. Both preferences of adult D. suzukii and offspring performance on intact versus dewaxed (epicuticular wax layer mechanically removed) grape berries were investigated in dual-choice assays. Moreover, the morphology and chemical composition of cuticular waxes and cutin of the different varieties were analyzed. Bioassays revealed that the epicuticular wax layer of most tested grape varieties influenced the preference behavior of adult flies; even less susceptible varieties became more susceptible after removal of these waxes. In contrast, neither offspring performance nor berry skin firmness were affected by the epicuticular wax layer. The wax morphology and the composition of both epi- and intracuticular waxes differed pronouncedly, especially between more and less susceptible varieties, while cutin was dominated by ω-OH-9/10-epoxy-C18 acid and the amount was comparable among varieties within sampling time. Our results highlight the underestimated role of the epicuticular surface and cuticle integrity in grape susceptibility to D. suzukii.

The morphology and chemical composition of cuticular waxes in some Brazilian liverworts and mosses

ABSTRACT Background The cuticle, by ensuring protection against water loss, was a key innovation in plant terrestrialisation. This layer is characterised by the cutin matrix embedded and covered with cuticular waxes. In this study we describe the cuticular waxes on gametophytes of several species of liverworts and mosses, including Brazilian endemics. Methods Cuticular waxes from 34 species from different locations in the São Paulo state, Brazil, were analysed by gas chromatography coupled with mass spectrometry. The compounds were identified based on mass spectra fragmentation. The morphology of the epicuticular waxes was analysed using scanning electron microscopy. Main results The wax content in the liverwort species varied from 0.1 to 4 μg cm−2, while in mosses the values ranged from 0.02 to 0.6 μg cm−2. The main classes of wax compounds were fatty acids, alkanes, and primary alcohols. Aldehydes, alkenes, esters, ketones, triterpenes, a diacid and a secondary alcohol had a more restricted distribution. The morphology of the epicuticular waxes was predominately of the film type. Conclusions In general, wax content was higher in the liverworts than in the mosses. Fatty acids and alkanes were the most common class whilst alkenes, ketones, diacid, and a secondary alcohol are described for the first time as wax compounds in bryophyte gametophytes.

The isolated or combined effects of dynamic controlled atmosphere (DCA) and 1-MCP on the chemical composition of cuticular wax and metabolism of ‘Maxi Gala’ apples after long-term storage

Apples have a continuous hydrophobic layer that covers the surface of the fruit, which is called the cuticle. The effects of 1-methylcyclopropene (1-MCP) on the cuticular wax layer of apples were reported after cold storage, although the interaction between 1-MCP and dynamic controlled atmosphere (DCA) is not yet known. Therefore, this study aimed to analyze the effects of 1-MCP on the wax composition and metabolism of ‘Maxi Gala’ apples after storage in a controlled atmosphere (CA) and dynamic controlled atmosphere based on chlorophyll fluorescence (DCA-CF) and respiratory quotient (DCA-RQ; RQ = 1.3 and 1.5). The 1-MCP treatment effectively decreased ethylene production for CA and DCA-CF treatments, while in DCA-RQ treatments produced no effect. The average extracted cuticular wax content of ‘Maxi Gala’ apples was 16.65 g m−2 and no differences in storage conditions or 1-MCP application were observed. Alkanes, alcohols, fatty acids, aldehydes, and terpenoids were identified in the chemical composition of the cuticular waxes, being alkanes and fatty acids the predominant ones. Moreover, 1-MCP decreased fatty acid and 10-nonacosanol concentrations in the fruit. Fruit with the 1-MCP application and stored in DCA had lower α-farnesene concentrations. The wax compositions of the DCA-stored apples with and without 1-MCP were similar. However, 1-MCP treatment resulted in a greater mass loss in fruit stored in DCA.

Chemical Composition of Cuticular Waxes and Pigments and Morphology of Leaves of Quercus suber Trees of Different Provenance.

The chemical composition of cuticular waxes and pigments and the morphological features of cork oak (Quercus suber) leaves were determined for six samples with seeds of different geographical origins covering the natural distribution of the species. The leaves of all samples exhibited a hard texture and oval shape with a dark green colour on the hairless adaxial surface, while the abaxial surface was lighter, with numerous stomata and densely covered with trichomes in the form of stellate multicellular hairs. The results suggest an adaptive role of leaf features among samples of different provenance and the potential role of such variability in dealing with varying temperatures and rainfall regimes through local adaptation and phenotypic plasticity, as was seen in the trial site, since no significant differences in leaf traits among the various specimens were found, for example, specific leaf area 55.6–67.8 cm2/g, leaf size 4.6–6.8 cm2 and photosynthetic pigment (total chlorophyll, 31.8–40.4 µg/cm2). The leaves showed a substantial cuticular wax layer (154.3–235.1 µg/cm2) composed predominantly of triterpenes and aliphatic compounds (61–72% and 17–23% of the identified compounds, respectively) that contributed to forming a nearly impermeable membrane that helps the plant cope with drought conditions. These characteristics are related to the species and did not differ among trees of different seed origin. The major identified compound was lupeol, indicating that cork oak leaves may be considered as a potential source of this bioactive compound.

Dynamic controlled atmosphere: Effects on the chemical composition of cuticular wax of ‘Cripps Pink’ apples after long-term storage

Abstract The effects of controlled atmosphere (CA) and dynamic controlled atmosphere based on chlorophyll fluorescence (DCA-CF) and respiratory quotient (DCA-RQ; RQ = 1.3 and 1.5) on the metabolism, decay incidence, concentration and chemical composition of ‘Cripps Pink’ apple peel wax after 8 months of storage plus shelf life at 20 °C were studied. DCA-RQ1.3 stored fruit had the lowest respiration rate, evidencing low metabolism, corroborating with the highest number of healthy fruit and consequently being the best storage condition. The mean wax concentration found 21.23 g m−2, although it was lower for the DCA-RQ1.5 condition after 7 d. There was increase in wax concentration for DCA treatments from 7 to 14 d of shelf life. Chromatographic analysis allowed the identification of palmitic, stearic, oleic and linoleic fatty acids, with an increase in cis-11,14-eicosadienoic acid in all treatments and in palmitic acid in CA at 14 d. Triterpenoids, such as ursolic acid and oleanolic acids, were higher in CA, while alcohols such as 10-nonacosanol was higher in both DCA-RQ treatments. All treatments had high concentrations of nonacosane and tetracosanal. DCA-RQ decrease the incidence of greasiness. The supposed induction of anaerobic metabolism by extremely low oxygen levels and consequently higher concentration of ethanol, which were monitored by the two levels of RQ, induced the formation of compounds that may favor some mechanisms of adaptation against the low oxygen partial pressure (pO2).

Compositional and morphological analyses of wax in northern wild berry species

Aerial surfaces of plants are covered by a waxy cuticle protecting plants from excessive water loss and UV light. In the present study, composition and morphology of cuticular waxes of northern wild berry species bilberry (Vaccinium myrtillus L.), lingonberry (V. vitis-idaea L.), bog bilberry (V. uliginosum L.) and crowberry (Empetrum nigrum L.) were investigated. Scanning electron microscopy (SEM) revealed differences in epicuticular wax morphology, and gas chromatography–mass spectrometry (GC–MS) analysis confirmed variation in chemical composition of cuticular waxes between the berry species. The dominant compounds in bilberry and lingonberry cuticular waxes were triterpenoids, while fatty acids and alkanes were the dominant ones in bog bilberry and crowberry, respectively. Wax extracted by supercritical fluid extraction (SFE) from industrial press cakes of bilberry and lingonberry contained linoleic acid and γ-linolenic acid as the dominant compounds. Furthermore, in vitro sun protection factor (SPF) of berry waxes depicted good UV-B absorbing capacities.

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

Wheat (Triticum aestivum L.) is an important food crop, and biotic and abiotic stresses significantly impact grain yield. Wheat leaf and stem surface waxes are associated with traits of biological importance, including stress resistance. Past studies have characterized the composition of wheat cuticular waxes, however protocols can be relatively low-throughput and narrow in the range of metabolites detected. Here, gas chromatography-mass spectrometry (GC-MS) metabolomics methods were utilized to provide a comprehensive characterization of the chemical composition of cuticular waxes in wheat leaves and stems. Further, waxes from four wheat cultivars were assayed to evaluate the potential for GC-MS metabolomics to describe wax composition attributed to differences in wheat genotype. A total of 263 putative compounds were detected and included 58 wax compounds that can be classified (e.g., alkanes and fatty acids). Many of the detected wax metabolites have known associations to important biological functions. Principal component analysis and ANOVA were used to evaluate metabolite distribution, which was attributed to both tissue type (leaf, stem) and cultivar differences. Leaves contained more primary alcohols than stems such as 6-methylheptacosan-1-ol and octacosan-1-ol. The metabolite data were validated using scanning electron microscopy of epicuticular wax crystals which detected wax tubules and platelets. Conan was the only cultivar to display alcohol-associated platelet-shaped crystals on its abaxial leaf surface. Taken together, application of GC-MS metabolomics enabled the characterization of cuticular wax content in wheat tissues and provided relative quantitative comparisons among sample types, thus contributing to the understanding of wax composition associated with important phenotypic traits in a major crop.

Cuticular wax composition of ‘Celeste’ and ‘Somerset’ cherry fruit

The cuticular layer plays an important role in protecting fruits against water loss and invasive microorganisms and insects, both during on-tree development and postharvest storage. There is also experimental evidence that cuticle composition and structure may be a relevant factor accounting for firmness and other textural attributes. Waxes are important cuticle components, together with the polymer matrices cutin and cutan. In this work, the chemical composition of waxes in the skin of 'Celeste' and 'Somerset' cherry (Prunus avium L.) fruit, which display quite different firmness levels, was investigated by means of gas chromatography-mass spectrometry (GC-MS). Fruit were picked at commercial maturity, and cuticles isolated enzimatically at harvest and after 3 days at 20°C. Total waxes were identified and quantified by means of GC-MS and GC-FID, respectively. In all cases, the most abundant constituent of cuticular waxes was the triterpene ursolic acid, which accounted for 49-56% ('Celeste') and 47% ('Somerset') of total wax composition. Important amounts of the alkanes nonacosane (6-10%, depending on cultivar and days at 20°C) and heptacosane (1-2%), as well as of the fatty acid linoleic acid (5-10%), were also found. Total alkane content was higher in 'Somerset' than in 'Celeste', but in contrast 'Celeste' cuticles were richer in triterpenes and fatty acids than those isolated from 'Somerset', thus showing some cultivar-related differences in the chemical composition of cuticular waxes.

Low vapor pressure deficit reduces glandular trichome density and modifies the chemical composition of cuticular waxes in silver birch leaves.

Cuticular wax layer is the first barrier against the outside environment and the first defense encountered by herbivores and pathogens. The effects of environmental factors on cuticular chemistry, and on the formation of glandular trichomes that account for the storage and secretion of lipophilic compounds to the leaf surface are poorly understood. Low vapor pressure deficit (VPD) has shown to reduce the nitrogen (N) status of plants. Thus, we studied the effects of elevated air humidity, indicated as VPD, and the effect of N fertilization on cuticular waxes and glandular trichome density in silver birch (Betula pendula Roth). Experiments were carried out in growth chambers with juvenile plants and in a long-term field experiment with older trees. Low VPD reduced the glandular trichome density in both experiments, in chamber and in field. The contents of the major triterpenoid and flavonoid aglycones correlated positively with glandular trichome density, which supports the role of trichomes in the exudation of secondary compounds to the leaf surface. A closer examination of the cuticular wax chemistry in the chamber experiment revealed that low VPD and N supply affected the composition of cuticular waxes, but not the total wax content. The deposition of different wax compounds followed a co-ordinated pattern in birch leaves, but different compound groups varied in their responses to N fertilization and low VPD. Low VPD reduced the hydrophobicity of cuticular waxes, as demonstrated by lower alkane content and less hydrophobic flavonoid profile in low VPD than in high VPD. Reduced hydrophobicity of the wax layer is presumed to increase leaf wettability. Together with reduced trichome density in low VPD it may enhance the susceptibility of trees to fungal pathogens and herbivores. High N supply under low VPD reduced the effect of low VPD on the cuticular wax composition. Total fatty acid content and the expression of β-amyrin synthase were lower under high N supply than under moderate N supply irrespective of VPD treatment. Nitrogen availability and decreasing VPD will modify leaf surface properties in silver birch and thereby affect tree defence against abiotic and biotic stress factors that emerge under climate change.

Investigations on the chemical composition of cuticular waxes in twelveFragariaL. genotypes

Cuticular waxes play an important role in the defence system of plants. To date, reports on the chemistry of waxes from the genus Fragaria L. are very scarce and only related to the cultivated strawberry F. × ananassa. In this study, the chemical composition of cuticular waxes in different genotypes of strawberries are described for the first time extensively. Cuticular waxes were then extracted separately from the ad- and abaxial surfaces of fully developed and pathogen free leaves from greenhouse cultivation using chloroform as an apolar organic solvent. Additionally, for adaxial surfaces the epi- and intracuticular wax layers were analysed separately. The quantitative composition was studied by gas chromatography (GC) with flame ionisation detection and single compounds were identified by coupled GC-mass spectrometry. Substantial differences in total mass and relative composition between the ab- and adaxial leaf sides and between different genotypes were detected with alkanes, fatty acid alkyl esters and aldehydes representing major compound classes. Other aliphatic compounds, triterpenoids and non-identified substances were detected only in minor quantities. Additionally, cinnamic acid alkyl esters were found exclusively on adaxial sides whereas secondary alcohols were only present on abaxial sides. Similar differences could be detected between the epi- and intracuticular layer of adaxial leaf surface. The chemistry of cuticular waxes can influence infection processes of pathogens in different ways. Therefore, the obtained results can be used in forthcoming investigations about resistances to fungal, bacterial and animal pathogens.

Variations of Leaf Cuticular Waxes Among C3 and C4 Gramineae Herbs

Modern C4 plants are commonly distributed in hot and dry environments whereas C3 plants predominate in cool and shade areas. At the outmost of plant surface, the deposition and chemical composition of cuticular waxes vary under different environmental conditions. However, whether such variation of cuticular wax is related to the distribution of C3 and C4 under different environmental conditions is still not clear. In this study, leaves of six C3 Gramineae herbs distributed in spring, Roegneriakamoji, Polypogonfugax, Poaannua, Avenafatua, Alopecurusaequalis, and Oplismenusundulatifolius, and four C4 and one C3 Gramineae herbs distributed in summer, Digitariasanguinalis, Eleusineindica, Setariaviridis, S. plicata, and O. undulatifolius, were sampled and analyzed for cuticular wax. Plates were the main epicuticular wax morphology in both C3 and C4 plants except S.plicata. The plates melted in C4 plants but not in C3 plants. The total cuticular wax amounts in C4 plants were significantly lower than those in C3 plants, except for O.undulatifolius. Primary alcohols were the most abundant compounds in C3 plants, whereas n-alkanes were relatively the most abundant compounds in C4 plants. C29 was the most abundant n-alkane in C3 plants except for O.undulatifolius, whereas the most abundant n-alkane was C31 or C33 in C4 plants. The average chain length (ACL) of n-alkanes was higher in C4 than in C3 plants, whereas the ACL of n-alkanoic acids was higher in C3 than C4 plants. The cluster analysis based on the distribution of n-alkanes clearly distinguished C3 and C4 plants into two groups, except for O.undulatifolius which was grouped with C4 plants. These results suggest that the variations of cuticular waxes among C3 and C4 Gramineae herbs are related to the distribution of C3 and C4 plants under different environmental conditions.

Solvent Effects on the Ultrastructure and Chemical Composition of Cuticular Wax and Its Potential Bioactive Role Against Alternaria alternata in Pingguoli Pear

Effects of different polarity solvents on the ultrastructure and chemical composition of cuticular wax in Pingguoli pear as well as their bioactive role against Alternaria alternate were studied and the results showed that the highest wax content was extracted with chloroform, and its wax content was up to 322.2 μg cm−2. Long-chain fatty acids predominated in menthol extracts and n-alkanes were predominant in wax extracted with ether, chloroform and n-hexane. Pingguoli pear fruit surface was covered by a smooth and amorphous wax layer with small, scattered crystal. The morphology of recrystallized wax in vitro after removal with different solvents was not similar to that of the intact fruit surface. Removal of cuticular wax with various solvents significantly enhanced A. alternata infection, except for wax removed by methanol. The solvent extracts of methanol and chloroform stimulated the spore germination and mycelium growth of A. alternata, but the ether and n-hexane extracts showed antifungal activity.

Chemical composition of cuticular waxes during fruit development of Pingguoli pear and their potential role on early events of Alternaria alternata infection.

To elucidate the role of fruit wax in fungal infection, changes in chemical composition of wax during fruit development of Pingguoli pear, and their role in Alternaria alternata infection were studied. Results showed that wax content increased during fruit development. Fruit harvested 130 days after full bloom (DAFB) had a peak wax content that was eight times higher than from fruit at 100 DAFB. There were differences in the relative chain-length distribution of wax classes during development. Alkanes were major components during early development, whereas alkanes and triterpenoids predominated during late development. Results of in vitro tests showed that conidial germination and mycelial growth of A. alternata could be inhibited by wax extracted from the fruit surface at different developmental stages. These results shed new light on the chemical basis for wax involvement in fungal infection.

The chemical composition of cuticular waxes from leaves of the gboma eggplant (Solanum macrocarpon L.)

The gboma eggplant (Solanum macrocarpon L.) is an important but still underutilized African green leafy vegetable. During the screening of the leaf cuticular waxes from Solanum plants, an unusual profile with elevated sterols and low hydrocarbon contents was detected for S. macrocarpon cv. UVPP. Detailed analysis of waxes from two cultivars has shown that sterols are made up of 19 and 32% of total wax, which has not yet been reported for any other plant species. The large content of phytosterols in surface lipids may generally reflect a overall high level of these compounds in the whole plant. Moreover, among the common plant triterpenes, we also found δ-amyrin, which was not previously reported as a component of leaf cuticular waxes. The hydrocarbon content was 6–13 times lower than in surface lipids of the closely related eggplant (Solanum melongena L.). Plant long-chain hydrocarbons are believed to be non-toxic for mammals. However, several cases of massive deposits of plant n-alkanes in the livers and lungs of animals and humans have been reported in the past. Certain plant features are promoted over others during the domestication process. We suggest that the hydrocarbon level in the surface lipids, which could affect the roughness and appearance of the leaves, might be one such characteristic.