Plant Epicuticular Waxes Research Articles

Project ChemicalBlooms: Collaborating with citizen scientists to survey the chemical diversity and phylogenetic distribution of plant epicuticular wax blooms.

Plants use chemistry to overcome diverse challenges. A particularly striking chemical trait that some plants possess is the ability to synthesize massive amounts of epicuticular wax that accumulates on the plant's surfaces as a white coating visible to the naked eye. The ability to synthesize basic wax molecules appears to be shared among virtually all land plants, and our knowledge of ubiquitous wax compound synthesis is reasonably advanced. However, the ability to synthesize thick layers of visible epicuticular crystals ("wax blooms") is restricted to specific lineages, and our knowledge of how wax blooms differ from ubiquitous wax layers is less developed. Here, we recruited the help of citizen scientists and middle school students to survey the wax bloom chemistry of 78 species spanning dicot, monocot, and gymnosperm lineages. Using gas chromatography-mass spectrometry, we found that the major wax classes reported from bulk wax mixtures can be present in wax bloom crystals, with fatty acids, fatty alcohols, and alkanes being present in many species' bloom crystals. In contrast, other compounds including aldehydes, ketones, secondary alcohols, and triterpenoids were present in only a few species' wax bloom crystals. By mapping the 78 wax bloom chemical profiles onto a phylogeny and using phylogenetic comparative analyses, we found that secondary alcohol and triterpenoid-rich wax blooms were present in lineage-specific patterns that would not be expected to arise by chance. That finding is consistent with reports that secondary alcohol biosynthesis enzymes are found only in certain lineages but was a surprise for triterpenoids, which are intracellular components in virtually all plant lineages. Thus, our data suggest that a lineage-specific mechanism other than biosynthesis exists that enables select species to generate triterpenoid-rich surface wax crystals. Overall, our study outlines a general mode in which research scientists can collaborate with citizen scientists as well as middle and high school classrooms not only to enhance data collection and generate testable hypotheses but also to directly involve classrooms in the scientific process and inspire future STEM workers.

An increased wax load on the leaves of goji plants (Lycium barbarum) results in increased resistance to powdery mildew

Abstract Background Goji (Lycium barbarum) is an important economic crop that is widely cultivated in Northwest China and is known as superfood. Goji plants are often affected by powdery mildew (Arthrocladiella mougeotii) in the field, resulting in considerable reduction in production and serious economic losses. The long-term reliance on agricultural chemicals to control powdery mildew not only leads to environmental pollution, but also causes excessive residues to accumulate in fruits, endangering human health. The plant epicuticular wax is the first physical barrier between land plants and the atmospheric environment, and plays an important role in the interactions of plants with pathogenic microorganisms. However, the relationship between epicuticular wax and powdery mildew resistance in goji plants is not well understood. Results The leaf epicuticular wax crystals of ‘Ningqi I’ goji were dense and small, and the wax load was 121.74 μg/cm2, which was 3.36 times greater than that of ‘Huangguo’ goji. The ratio of alcohol components in ‘Ningqi I’ goji was 121.18% greater than that in ‘Huangguo’ goji. The incidence rate and disease index of ‘Ningqi I’ goji inoculated with powdery mildew were significantly lower than those inoculated ‘Huangguo’ goji, showing high resistance and moderate susceptibility, respectively. After mechanical wax removal, the disease indices of the two goji varieties increased significantly, indicating extreme susceptibility. Seventeen differential expression genes showing significantly greater expression in ‘Ningqi’ goji leaves than in ‘Huangguo’ goji leaves were enriched in genes involved in fatty acid elongation and the wax biosynthesis pathway. The FAR activity and relative expression levels of LbaFAR and LbaWSD1 in ‘Ningqi I’ goji were significantly greater than those in ‘Huangguo’ goji. The relative expression levels of these genes significantly increased in the overexpression tobacco lines FAR-OE and WSD1-OE, and the wax load were augmented by 46.10% and 22.23%, respectively. Conclusions The increased expression of the LbaFAR and LbaWSD1 genes in ‘Ningqi I’ leaves led to increased FAR and WSD1 activity, increasing the wax load and alcohol content of the epicuticular of leaves, and improving leaf glossiness, resulting in strengthened resistance to powdery mildew. Therefore, the production of leaf epicuticular wax mediated by the LbaFAR and LbaWSD1 genes could be the main reason for the difference in powdery mildew resistance between the two goji varieties, which can provide a theoretical basis for the selection of resistant varieties to control goji powdery mildew. Graphical Abstract

Combined Effect of Different Flower Stem Features on the Visiting Frequency of the Generalist Ant Lasius niger: An Experimental Study.

Simple SummaryFlowering plants usually attract insect pollinators by offering them nectar, pollen or other energetically valuable sources. To deter ants, which are unreliable pollinators and can act as nectar thieves, plants have developed different systems either inside the flowers or associated with the stems. The latter one, called greasy pole syndrome, is based on the combined effect of several stem features hampering the access of ants to the apically located flowers. In this study, we examined the effects of different flower stem features in the round-leaved Alexanders Smyrnium rotundifolium on the visiting frequency of the generalist ant species, the black garden ant Lasius niger. We conducted the experiments with ants running on dry wooden sticks mimicking four different types of stems. To attract ants, we placed a sweet sugar syrup droplet on a stick tip. Ants visited different types of stem-mimicking sticks with significantly different frequencies. The highest number of insects were registered on untreated stick samples, whereas the lowest visiting frequency was observed on sticks bearing cuff-like structures (serving as macroscopic physical barriers) covered with a nano/microparticle film, which caused the slipperiness of the surface. Thus, by combining macroscopic obstacles and slippery surfaces, plants can protect their flowers from undesirable crawling visitors such as ants.In order to understand the effects of the morphology and surface texture of flower stems in Smyrnium rotundifolium on the visiting frequency of generalist ants, we conducted experiments with Lasius niger ants running on dry wooden sticks mimicking different types of stems: (1) intact (grooved) sticks; (2) sticks painted with slaked (hydrated) lime (calcium carbonate coverage) imitating plant epicuticular wax coverage; (3) intact sticks with smooth polyester plate-shaped cuffs imitating upper leaves; and (4) intact sticks bearing cuffs painted with slaked lime. Ants were attracted by the sweet sugar syrup droplets placed on a stick tip, and the number of ants visiting the drops was counted. Our data showed significant differences in the visiting frequencies between the different types of stem-mimicking samples. The number of recorded ants progressively decreased in the following order of samples: intact sticks—painted sticks—sticks with intact cuffs—sticks with painted cuffs. These results clearly demonstrated that micro/nanoscopic surface coverages and macroscopic physical barriers, especially if combined, have a negative impact on the attractiveness of stems to ants. This study provides further evidence for the hypothesis that having a diversity of plant stems in the field, generalist ants prefer substrates where their locomotion is less hindered by obstacles and/or surface slipperiness.

Hydrophobic Waxes in Ivory Nuts Affect Surface Modification by Atmospheric Air Plasma Jet

Ivory nuts, bioproducts from South American palms, possess a hard, water-insoluble, and microporous endosperm with a strong resemblance to elephant ivory. The nuts sustainable appeal made them popular as eco-friendly substitutes to ivory and, more recently, microbeads. However, their hygroscopicity and mannan composition impart susceptibility to deterioration by microbes and insects. Cold plasma treatment has been widely investigated as a clean and cost-effective procedure for seed disinfection and surface modification. Hence, in this work, ivory nut endosperm was treated by an air plasma jet to modify wettability. Plasma treated samples were characterized by the water contact angle, AFM, and Raman imaging. Water contact angle results presented an increase from (31.5 ± 8.7)º to (78.9 ± 5.4)º, demonstrating surface hydrophobization. This result was attributed to the modification of surface chemistry by migration and repolymerization of extractives promoted by plasma treatment. AFM results evidenced the formation of a heterogeneous layer containing lamellar features similar to plant epicuticular waxes. Besides, principal component analysis of Raman imaging results highlighted spectral contributions from wax, xylan, mannan, and lignin. These results demonstrate that atmospheric air plasma jets can be employed for ivory nut hydrophobization with no need for additional precursors, altering surface chemistry by crosslinking endosperm native substances.

Cuticular wax composition of mature leaves of species and hybrids of the genus Prunus differing in resistance to clasterosporium disease

The interaction of a host plant with pathogen implies an extremely complex process involving the outer waxy layer of the cuticle, cutin, cell membrane, and intracellular structures. However, the initial contact between plants and pathogens takes place in cuticular waxes covering the surface of leaves, stems and fruits. Despite many findings on the role of plant epicuticular waxes, there is a gap in the understanding of the relationship between individual compounds and their functions. The pathogenic fungus Clasterosporium carpohilum (Lev.) Aderh. parasitizes the tissues of many stone fruit trees, damaging leaf and fruit surface. The aim of this work was to find out if the quantity and composition of leaf epicuticular wax could be responsible for the resistance to clasterosporium disease. The study of differences of plants in fungal resistance was carried out on species and hybrids of the genus Prunus from the collection of the Botanical Garden of Oles Honchar Dnipro National University (Dnipro city, Ukraine). The chloroform extracts of epicuticular waxes from the surface of mature leaves were analyzed by gas chromatography connected to mass-spectrometry. GC/MS assay was performed using Shimadzu GCMS-QP 2020 El equipped with capillary column (5% diphenyl/95% dimethyl polysiloxane), and helium as a carrier gas. Mass Spectrum Library 2014 for GSMS was used to identify the separated compounds of the wax extracts. The maximum total wax amount on the adaxial and abaxial leaf surface of hybrid 2 was twice the minimum wax accumulation for hybrid 4. Overall, 20 individual compounds belonging to six hydrocarbon classes were identified. Leaf epicuticular wax composition both in Prunus persica (L.) Batsch and P. dulcis (Mill.) D. A. Webb, and hybrids was dominated by long-chain n-alkanes with even carbon number (77.6–90.9% of total sum). The alkenes’ class was represented only by 17-pentatriacontene detected in the wax of both Prunus species. Octadecanaldehyde was found in epicuticular wax of P. dulcis while absent in wax of the more resistant species P. persica. Prime alcohols 1-tetradecanol and 1-hexacosanol were detected in leaf waxes of hybrid 4 and P. dulcis respectively. The ester class contained seven compounds found in leaf epicuticular waxes of both plant species and all hybrid forms. The identification of phthalic acid esters in leaf wax extracts was unexpected, and the phthalates’ origin is discussed. Strong positive correlation between leaf damage and tetrapentacontane content in epicuticular waxes could presumably be the result of infection-induced metabolism reprogramming in epidermal cells of infected leaves.

Relationship between the amount and composition of epicuticular wax and tolerance of Ipomoea biotypes to glyphosate

Ipomoea species are troublesome weeds in crop systems through Brazil. Drought stress typically reduces glyphosate efficacy by reducing the foliar uptake of herbicides and their translocation. Using both glyphosate tolerant (GT) and sensitive (GS) plants from Ipomoea grandifolia, I. indivisa and I. purpurea species, this research aimed to (a) correlate amounts of epicuticular wax and tolerance to glyphosate in plants and (b) determine the effect of drought stress (DStress) on changes in the quantity and chemical composition of plant epicuticular waxes. The dose that causes 50% inhibition of growth (GR50) of the biotypes varied between 62 and 1208 (I. grandifolia), 159 and 913 (I. indivisa), and 389 and 1925 g a.e. ha−1 of glyphosate (I. purpurea). There was low inverse correlation (–0.46) between the amount of epicuticular wax and the sensitivity to glyphosate. GT biotypes of the species presented greater plastic capacities than GS biotypes for increasing the amount of epicuticular wax under DStress. The three Ipomoea species exhibited different chemical profiles of waxes supported by IR spectra, which allows for their differentiation. For I. grandifolia and I. purpurea, there was an increase in the polar components in the state without DStress, while for the species I. indivisa, no differences in infrared spectra were detected between the two water conditions.

Complementarity of Raman and Infrared Spectroscopy for Structural Characterization of Plant Epicuticular Waxes

Raman and infrared (IR) are two complementary vibrational spectroscopy techniques that enable label-free, noninvasive, and nondestructive structural characterization of analyzed specimens. IR spect...

FT-RAMAN AND GC/MS OF EXTRACT AND EPICUTICULAR WAXES OF ANACARDIUM OCCIDENTALE L. LEAVES FROM AMAZON

Anacardium occidentale is a globally known plant and has great economic importance in the food and resins industry. In traditional medicine, several uses are made of leaves in the treatment of gastrointestinal and skin diseases. Its biological properties have been confirmed in antioxidant, antimicrobial and anti-inflammatory studies. This work aimed to analyze the chemical composition of the ethanolic extract and the wax epicuticulares of the leaves of A. occidentale by means of the Gas Chromatography (GC/MS) and Raman Spectroscopy (FT-Raman) techniques. FT-Raman analysis showed a stretch of the C-H2, characteristic band in plant epicuticular waxes. In CG/MS a complex of aliphatic and cyclic mixtures was observed, among them alkanes and triterpenes. In the ethanolic extract the terpenes were the majority compounds by CG/MS. The knowledge of the chemical composition of A. occidentale, mainly of the epicuticular waxes, is important due to its relevance in the market, and it becomes a starting point for new studies of agroecological knowledge, such as the properties of epicuticular waxes in the interaction with the environment , pathogens and herbicides, and also for the search of new pharmacological properties.

Nanoscale Structural Organization of Plant Epicuticular Wax Probed by Atomic Force Microscope Infrared Spectroscopy.

The cuticle covers external surfaces of plants, protecting them from biotic and abiotic stress factors. Epicuticular wax on the outer surface of the cuticle modifies reflectance and water loss from plant surfaces and has direct and indirect effects on photosynthesis. Variation in epicuticular wax accumulation, composition, and nanoscale structural organization impacts its biological function. Atomic force microscope infrared spectroscopy (AFM-IR) was utilized to investigate the internal and external surfaces of the cuticle of Sorghum bicolor, an important drought-tolerant cereal, forage, and high-biomass crop. AFM-IR revealed striking heterogeneity in chemical composition within and between the surfaces of the cuticle. The wax aggregate crystallinity and distribution of chemical functional groups across the surfaces was also probed and compared. These results, along with the noninvasive nondestructive nature of the method, suggest that AFM-IR can be used to investigate mechanisms of wax deposition and transport of charged molecules through the plant cuticle.

Nuclear DNA based species delineations ofCoccusscale insects in symbiosis with plants and ants, and the role of plant epicuticular wax in structuring associations

We undertook phylogenetic analysis of nuclear DNA to elucidate species boundaries in the symbiotic Coccus scale insects associated with mutualistic Crematogaster ants and Macaranga plants occurring in the ever-wet forests of Southeast Asia. The coccid specimens clustered into ten lineages, each corresponding to a morphospecies assignment. The lineage identified as C. secretus was separated from the Main Clade by an outgroup. We also examined all pairwise associations among the three symbiont guilds to understand how patterns of association were structured. The analyses revealed that each ant, plant or coccid operational (taxonomic) unit often associated with multiple O(T)Us of each of the other two guilds. However, where testing was feasible, a ‘preference’ for one or sometimes two partner O(T)Us of each guild was often detected. Mutual ‘preferences’ or ‘avoidances’ were relatively common among the symbionts, and no conflicts of interest were apparent. The network of preferred partners among all three guilds showed compartmentalization structured by the presence/absence of plant epicuticular wax, suggesting that this feature plays a fundamental role in how the symbionts select partners that best serve their needs. To a lesser degree, the network was also structured by whether the host plant stems were ant-excavated or hollowed naturally.

Hydroxy fatty acids in snow pit samples from Mount Tateyama in central Japan: Implications for atmospheric transport of microorganisms and plant waxes associated with Asian dust

AbstractWe report here the source apportionment of atmospheric soil microorganisms and higher plant metabolites based on chemical markers (hydroxy fatty acids: FAs) in the snowpack samples collected from Mount Tateyama in central Japan during spring 2009 (N = 6) and 2011 (N = 7). A homologous series of β‐hydroxy FAs (C9–C20), constituents of Gram‐negative bacteria (GNB), in snowpacks clearly suggest a long‐range atmospheric transport of dust‐associated bacteria followed by scavenging by snowflakes. Similarly, higher atmospheric abundances of α‐(C16–C32) and ω‐(C9–C30)‐hydroxy FAs in the snow layers containing Asian dust revealed contributions from soil microbes and higher plant epicuticular waxes. Moreover, covariation between the concentrations of hydroxy FAs and water‐soluble Ca2+ (dust tracer), together with calculated air mass backward trajectories, demonstrated their source regions such as the Taklamakan Desert, Gobi Desert, and Loess Plateau. A close match of molecular distributions of hydroxy FAs (with the predominance of ω‐ and β‐isomers) is noteworthy between snowpack (present study) and springtime aerosols from Chichijima Island in the western North Pacific (WNP). This observation suggests a “below‐cloud scavenging” of transported dust particles and associated soil microbes in the East Asian outflow by snowflakes. These distributions are, however, contrary to those observed in the fresh snow samples from Sapporo, northern Japan (predominance of α‐hydroxy FAs), which could be explained by “in‐cloud” microbial oxidation processes. This comparison, therefore, provides additional insights regarding the aeolian transport of soil microbes in the East Asian outflow to the WNP, which has not been available.

Demonstrating the Effect of Surfactant on Water Retention of Waxy Leaf Surfaces

We report here the development of an inexpensive and engaging laboratory-based activity that can help students learn about the scientific method and the role of plant epicuticular waxes and surfactant function on waxy plant leaves as real life example in the agricultural industry. Three each of nontreated collard leaves (Brassica oleraceae L. Acephala group) and brushed-leaves were sprayed with water to demonstrate hydrophobicity of epicuticular waxes. Another set of three nontreated collard leaves was sprayed with Tween 20 containing water to demonstrate function of surfactant. Then, water retention rate was calculated by subtracting between before and after spray treatments. Water contact angles were measured by ImageJ software from nontreated and brushed-leaves from pictures taken by students’ smartphone. This lab activity provides a foundation for instruction on the importance of the plant epicuticular waxes that is the outermost hydrophobic barrier in agrochemical applications and the function of sur...

Spruce budworm feeding and oviposition are stimulated by monoterpenes in white spruce epicuticular waxes.

Monoterpenes, source of the distinctive odor of conifers, are generally considered plant defensive compounds. However, they are also known to act as long-range insect attractants, as they are volatile and permeate forest airspaces. Moreover, they are lipid soluble and can be absorbed into plant epicuticular waxes. We test their role in short-range host plant choice by both adult females and larvae of a folivorous forest pest (Choristoneura fumiferana). We conducted laboratory assays testing the responses of Eastern spruce budworm to an artificial monoterpene mix (α-pinene, β-pinene, limonene, myrcene) and to white spruce (Picea glauca) epicuticular waxes in closed arenas. Ovipositing females preferred filter paper discs treated with P. glauca waxes to controls, and preferred the waxes + monoterpenes treatment to waxes alone. However, females showed no preference between the monoterpene-treated disc and the control when presented without waxes. Feeding larvae prefered wax discs to control discs. They also consumed discs treated with realistic monoterpene concentrations and wax preferentially over wax-only discs, but showed no preference between extremely high monoterpene concentrations and wax-only controls. In an insect-free assay, P. glauca epicuticular wax decreased monoterpene volatilization. These results suggest that P. glauca waxes and realistic concentrations of monoterpenes are stimulatory to both egg-laying females and feeding larvae, and that their effects are synergistic.

Variations in leaf epicuticular n-alkanes in some Broussonetia, Ficus and Humulus species

n-Alkanes are biosynthesized from very long-chain fatty acid wax precursors and its distribution grants the most useful taxonomic contribution for plant species. In current study, five species from three genera of Moraceae family were sampled separately from three areas (Mountain Jin-yun, Mountain Jin-fo and Bei-bei) in Chongqing, China, namely, Broussonetia papyrifera, Broussonetia kazinoki, Ficus virens, Ficus tikoua, and Humulus scandens. The amounts of n-alkanes in epicuticular wax enabled discrimination among areas, varying from 4.9 μg cm−2 to 16.9 μg cm−2 in Mountain Jin-yun, 6.9 μg cm−2 to 20.5 μg cm−2 in Bei–bei, and 4.7 μg cm−2 to 61.7 μg cm−2 in Mountain Jin-fo, respectively. Among the five species, the amount of n-alkanes was the highest in B. papyrifera and the lowest in F. tikoua for all areas, showing high species variation. The most abundant n-alkanes in all investigated species were two odd-numbered n-alkanes, i.e., C29 and C31. The epicuticular waxes of H. scandens from Bei-bei had a higher relative abundance of C29 than other species from Mountain Jin-yun and Mountain Jin-fo. The chain length of n-alkanes from Bei-bei was longer than that from other areas. The even/odd predominance (EOP) or odd/even predominance (OEP) occurred in short-chain n-alkanes of plant epicuticular wax might be correlated with their growing environments. All Carbon Preference Index (CPIs) and Average Chain Length (ACLs) from Bei-bei were lower than those from other sampling areas, mainly attributing to the higher numbers of short- and mid-chain n-alkanes in plants from Bei-bei. Cluster analysis revealed that H. scandens from Bei-bei and F. virens from Mountain Jin-yun were different from other species. Based on these findings, it seems that environmental conditions contribute to the complex patterns and variation of n-alkanes and different plant species had different responses to environment changes. The distribution of n-alkanes could be a good indicator to distinguish plant species under different growing conditions before other obvious morphological changes could be observed.

Geochemical and ecological significance of soil lipids under Rhododendron ponticum stands

The bio-geographical significance of Rhododendron ponticum spp. baeticum (Ericaceae) as a relict species is well recognized. However, out of its native habitat it is an invasive exotic considered a major threat to natural ecosystems in areas of Atlantic Western Europe. The studies on the impact of Rhododendron influence on soil organic matter composition and associated ecological implications, i.e. presence of bioactive compounds with ecological significance, are limited. This work describes the soil lipid assemblage in three sites under Rhododendron stands and adjacent sites with deciduous oak (Quercus canariensis), both in their native habitats in Southern Spain (Sierra de Luna, Cádiz). The results are discussed in terms of organic matter dynamics and the presence of molecules that may be associated with Rhododendron invasive success. The soils are acid Xerochrepts formed on siliceous sands. Composite soil samples were taken at two depths (0–10 cm and 10–20 cm) and soxhlet extracted with a dichloromethane-methanol mixture (3:1). Soil lipid assemblage was studied by GC/MS after fractionation and appropriate derivatization of extracts. The qualitative chemical composition of soil extractable lipids under Rhododendron is reported here for the first time. Our results show that soil n-alkane and fatty acid distributions are compatible with an input from plant epicuticular waxes, as well as with the occurrence of selective preservation of long-chain fatty acids with depth. The pattern of short-chain n-alkanes found in surface samples indicates an anthropogenic contamination threat from nearby industrialized areas of “Campo de Gibraltar”. The presence of branched iso and anteiso C15 and C17, β-hydroxy fatty acids and the sterol brassicasterol points to high microbial soil activity. Finally, the pentacyclic triterpenes taraxerone and taraxerol were detected in soils with Rhododendron but not with Quercus. These are known bio-active plant compounds and could be related with the effectiveness of Rhododendron as an invasive exotic species.

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.

Fracture behaviour of plant epicuticular wax crystals and its role in preventing insect attachment: a theoretical approach

It is known that attachment ability of insects depends among others on the texture of the substrate. On plant surfaces, covered with microscopic epicuticular wax crystals, insect attachment was found to be highly reduced for many insect species. In some plants, this effect may be explained by the contamination of insect adhesive organs (pads) by wax crystals. In the present study, mechanics of the wax crystals fracture during contact formation between insect adhesive pads and plant surface is examined, in order to explain the observed contamination of pads by wax. It is shown that mechanisms of the wax crystal fracture may be rather different, depending on the slenderness ratio of the crystals. Crystals with high values of the ratio may buckle elastically or in an elastic-plastic way. For five plant species under consideration, the critical value of the slenderness ratio for elastic buckling is 26.5, while for elastic-plastic buckling it is 18.7. If the values of the slenderness ratio are lower than the critical values, one has to consider bending of the crystals under the weight of insects. Although this study considered only crystals of a tubular shape, the general approach is valid also for crystals of other shapes.

Organic Matter of the Troposphere—II.: Natural Background of biogenic lipid matter in aerosols over the rural western United States

Higher plant waxes are the predominant natural components in the lipid fractions (> C 15) of aerosols sampled over rural and oceanic regions. Hydrocarbon, fatty acid, ketone and fatty alcohol fractions of the lipids were characterized in terms of their contents of homologous compound series and specific biogenic molecular markers. Particulate samples from the rural western United States have been analyzed and compared with samples from urban Los Angeles and remote areas over the Atlantic Ocean. The samples from rural sites contained predominantly vascular plant wax and lesser amounts of higher plant sterols and resin residues. Urban samples and, to varying degrees, some rural samples contained primarily higher weight residues of petroleum products. The loadings of hydrocarbons derived from higher plant waxes ranged approximately from 10 to 160 ng m −3 of air (for fatty acids, 10–100 ng m −3 and for fatty alcohols, 10–200 ng m −3). Higher molecular weight lipids (i.e. plant epicuticular wax, terpenes, etc.) from flora comprise a significant component of the organic carbon in rural aerosols. Primary biogenic residues are major components of aerosols in all areas and they are important components in the global cycling of organic carbon.

Plant Epicuticular Waxes: Chemistry, Form, Self-Assembly and Function

Plant epicuticular waxes represent the outermost boundary layer of the majority of land plants. Based on their micromorphology and chemical composition they form a multifunctional surface. Their most important functions are the protection against uncontrolled water loss, reflection of solar radiation from UV to visible light, and their crucial influence on surface wettability and particle adhesion. The three-dimensional epicuticular wax crystals are of particular importance for the majority of these interfacial interactions. This article provides an overview on plant epicuticular waxes, focusing on chemical composition, morphology, self-assembly and function. It is dedicated to Prof. Dr. Eckhard Wollenweber on the occasion of his 65th birthday, and his continuous and fundamental work on a special class of plant secondary metabolites that are collectively called flavonoids.

Interaction of Plant Epicuticular Waxes and Extracellular Esterases of Curvularia eragrostidis during Infection of Digitaria sanguinalis and Festuca arundinacea by the Fungus

Curvularia eragrostidis, a causal agent of head blight on the weed (Digitariasanguinalis), did not cause disease on the turfgrass Festuca arundinacea. Differentextracellular esterase isoenzymes were detected in saprophytic and parasitic phases duringthe fungal germination. The epicuticular waxes of D. sanguinalis were more efficient toinduce the secretion of esterases from the fungus than that of F. arundinacea, but were morerapidly degraded by the fungal enzymes. Component analysis indicated that the epicuticularwaxes from D. sanguinalis were mostly composed of alcohols, with 54.3% being 9,12-Octadecadien-1-ol. The main component of F arundinacea waxes was alkyl compounds,with 49.8% being olefin, 9-Tricosence. More long-chained esters were found in D.sanguinalis waxes, which were easier to be digested than those in F. arundinacea waxes byextreacellular esterases of the fungus. Epicuticular waxes play a role in varyingpathogenicity of C. eragrostidis on D. sanguinalis and F arundinacea.