Ontogenetic variations in the composition of peach leaf wax

The composition of the epicuticular waxes from the adaxial and abaxial surfaces of peach leaves varies considerably during one season's growth. Triterpenoid acids are major components 84–95% of the waxes from the youngest leaves but the proportions of these constituents decrease as the leaves expand. The waxes from the abaxial surfaces of fully expanded leaves consist primarily of hydrocarbons (C_22–C34) and triterpenoid acids, whereas the adaxial surface waxes also contain large proportions of primary alcohols (C₂₆-C₃₄) and esters (C₄₂-C₅₂). The latter include sitosteryl esters of hexacosanoic, octacosanoic and eicosanoic acids. Variations were also noted between fully expanded leaves of different ages, the abaxial surface waxes of the oldest leaves containing the highest proportions of hydrocarbons, whilst the wax from the adaxial surface of the corresponding leaves contained the largest amounts of esters, sitosterol and hydrocarbons.     

Novel diterpenoids and hydrocarbons in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae)

Chemical constituents contained in the Dufour gland of the ectoparasitoid Habrobracon hebetor (Say) (Hymenoptera: Braconidae) were characterized. Three terpenes, beta-springene, a homo-beta-springene, and a homo-geranyllinalool constitute approximately 37% of the gland components, with the remaining 63% all being hydrocarbons. The hydrocarbons consist of a homologous series of n-alkanes (n-C21 to n-C31), a trace amount of 3-methyl C23, a homologous series of internally methyl-branched alkanes (11-methyl C23 to 13-methyl C35), one dimethylalkane (13,17-dimethyl C33), a homologous series of monoenes (C(25:1) to C(37:1)) with the double bonds located at Delta9, Delta13 and Delta15 for alkenes of carbon number 25 to 31 and at Delta13 and Delta15 for carbon numbers 33 to 37 and three homologous dienes in very low amounts with carbon numbers of 31, 32, and 33. The terpenoid and hydrocarbon composition of the Dufour gland was similar in virgin and mated females. However, in contrast to the hydrocarbons, the amount of beta-springene and homo-geranyllinalool increased significantly with time after adult emergence from the cocoon. Although many hydrocarbons in the Dufour gland are the same as those on the cuticle of this species [Howard and Baker, Arch. Insect Biochem. Physiol. 53:1-18 (2003)], substantial differences also occur. Of particular note is the chain length of alkenes and location of the double bonds: cuticular alkenes have a chain length of C23 to C29 and double bond locations at Delta5, Delta7, and Delta9, whereas the Dufour gland alkenes contains a greater range of carbon numbers and have no Delta5 or Delta7 alkenes. The Dufour gland contains only one of the long-chain dimethylalkanes found on the cuticle. Also, no terpenoids are found on the cuticle, and the Dufour gland contains none of the secondary wax esters that are major components on the cuticle. GC-MS analysis of lipids carried in the hemolymph of H. hebetor indicated that all hydrocarbons found on both the cuticle and in the Dufour gland are present, as are some of the wax esters. However, none of the terpenoids were detected in the hemolymph. This suggests that the hydrocarbons are synthesized in other tissues or cells, probably by oenocytes, and differentially partitioned between the cuticle and the Dufour gland. The terpenoids are most likely synthesized within the Dufour gland. Analysis of surface lipids from eggs laid within 18 h indicated that no diterpenoids were present. Rather, the lipids present on the eggs were n-alkanes, monomethylalkanes, alkenes, and secondary alcohol wax esters. This composition did not reflect that of the Dufour gland, hence eggs are not being coated with Dufour gland components during oviposition.     

Surface wax of Andreaea and Pogonatum species

The mosses Andreaea rupestris, Pogonatum aloides and P. urnigerum contain surface waxes in amounts of 0.05–0.12% dry wt. The waxes consisted of esters (C₃₈-C₅₄), primary alcohols (C₂₀-C₃₂), free fatty acids (C₁₆-C₃₀), and alkanes (C₂₁-C₃₁). Additionally, aldehydes (C₂₂-C₃₀) were major constituents in the wax of P. urnigerum. The classes and their chain length distributions in the surface waxes of these mosses are comparable to those of epicuticular waxes of higher plants.     

植物角质层蜡质的化学组成研究综述

角质层是植物与外界的第一接触面,而角质层蜡质则是由位于角质层外的外层蜡质和深嵌在角质层中的内层蜡质两部分构成。植物角质层蜡质成分极其复杂,具有重要的生理功能。综述了有关植物角质层蜡质的化学组成信息,探讨了目前植物角质层蜡质化学成分研究中存在的一些问题,展望了角质层蜡质成分的研究前景。     

The determination of n-alkanes in the cuticular wax of leaves of Ludwigia adscendens L

An n-hexane extract of fresh, mature leaves of Ludwigia adscendens, containing a thin layer of epicuticular waxes, has been analysed for the first time by TLC, IR and GC using standard hydrocarbons. The leaves contained 22 identified long chain (C15-C36) n-alkanes, accounting for 74.27% of the hydrocarbons present, and an unknown number of unidentified branched chain alkanes. The predominant n-alkane was C25 (11.02%), whilst C18 (7.62%), C20 (6.14%), C29 (5.36%) and C27 (5.29%) n-alkanes were moderately abundant: the C35 homologue was present only in minor amounts (0.22%).     

Waxes of the social spider Anelosimus eximius (Araneae,Theridiidae): Abundance of novel n-propyl esters of long-chain methyl-branched fatty acids

The pentane extract of the social spider, Anelosimus eximius (Araneae, Theridiidae), contains hydrocarbons, fatty acids and their methyl esters, and a series of novel propyl esters of long-chain methyl-branched fatty acids. The propyl esters comprise almost three-fourths of the extract and consist predominantly of odd-numbered carbon chain components. Mass spectrometric analyses of the propyl esters, their methyl esters and cyanide derivatives showed that mono-, di- and trimethyl branched components with methyl branches on even numbered carbons predominate. The major components are propyl 4,20- and 4,30-dimethylhentriacontanoate and propyl 6,20- and 6,30-trimethylhentriacontanoate. The hydrocarbon fraction consists of n-, monomethyl- and dimethylalkanes, containing a relatively high proportion of even-numbered carbon chain components. The abundance of even-numbered carbon chain length alkanes and odd-numbered carbon chain length fatty acyl groups, along with abundant methyl-branches suggest that the propionyl-CoA and its carboxylated product, methylmalonyl-CoA, play important roles in the biosynthesis of these unique waxes. Arch. Insect Biochem. Physiol. 36:295–314, 1997. © 1997 Wiley-Liss, Inc.     

Tomato fruit cuticular waxes and their effects on transpiration barrier properties: functional characterization of a mutant deficient in a very-long-chain fatty acid beta-ketoacyl-CoA synthase

Cuticular waxes play a pivotal role in limiting transpirational water loss across the plant surface. The correlation between the chemical composition of the cuticular waxes and their function as a transpiration barrier is still unclear. In the present study, intact tomato fruits (Lycopersicon esculentum) are used, due to their astomatous surface, as a novel integrative approach to investigate this composition- function relationship: wax amounts and compositions of tomato were manipulated before measuring unbiased cuticular transpiration. First, successive mechanical and extractive wax-removal steps allowed the selective modification of epi- and intracuticular wax layers. The epicuticular film consisted exclusively of very-long-chain aliphatics, while the intracuticular compartment contained large quantities of pentacyclic triterpenoids as well. Second, applying reverse genetic techniques, a loss-of-function mutation with a transposon insertion in a very-long-chain fatty acid elongase beta-ketoacyl-CoA synthase was isolated and characterized. Mutant leaf and fruit waxes were deficient in n-alkanes and aldehydes with chain lengths beyond C30, while shorter chains and branched hydrocarbons were not affected. The mutant fruit wax also showed a significant increase in intracuticular triterpenoids. Removal of the epicuticular wax layer, accounting for one-third of the total wax coverage on wild-type fruits, had only moderate effects on transpiration. By contrast, reduction of the intracuticular aliphatics in the mutant to approximately 50% caused a 4-fold increase in permeability. Hence, the main portion of the transpiration barrier is located in the intracuticular wax layer, largely determined by the aliphatic constituents, but modified by the presence of triterpenoids, whereas epicuticular aliphatics play a minor role.     

蚧虫蜡泌物的化学研究进展

总结了国内外对蚧虫蜡泌物及其化学成分的研究进展 ,内容包括蜡泌物形成介壳的主要类型 ;蜡泌物的化学研究方法及已涉及的种类 ;蜡泌物的主要化学组成 ,并对 5类物质 ,即蜡、烃类、树脂或萜类、色素类、内蜜露作了重点叙述。最后 ,讨论了研究蚧虫蜡泌物的化学成分具有的意义和应用前景 ,包括蜡泌物作为生物资源的利用 ;以蚧虫作为农林、果树和花卉业的重要害虫 ,针对蜡泌物的特点研制相应的新型杀虫剂 ;利用蜡泌物的化学信息素对天敌的诱导作用 ,开展蚧虫生物防治 ;利用蜡泌物作为化学分类性状的应用等。     

Cuticular waxes from potato (Solanum tuberosum) leaves

The qualitative and quantitative compositions of leaf cuticular waxes from potato (Solanum tuberosum) varieties were studied. The principal components of the waxes were very long chain n-alkanes, 2-methylalkanes and 3-methylalkanes (3.1-4.6 microg cm(-2)), primary alcohols (0.3-0.7 microg cm(-2)), fatty acids (0.3-0.6 microg cm(-2)), and wax esters (0.1-0.4 microg cm(-2)). Methyl ketones, sterols, beta-amyrin, benzoic acid esters and fatty acid methyl, ethyl, isopropyl and phenylethyl esters were found for the first time in potato waxes. The qualitative composition of the waxes was quite similar but there were quantitative differences between the varieties studied. A new group of cuticular wax constituents consisting of free 2-alkanols with odd and even numbers of carbon atoms ranging from C25 to C30 was identified.     

Homologous very-long-chain 1,3-alkanediols and 3-hydroxyaldehydes in leaf cuticular waxes of Ricinus communis L

Surface extracts from primary leaves of Castor bean were found to contain 1.8 microg cm(-2) of cuticular waxes. The mixture comprised alkanes (C(26)-C(29)), primary alcohols (C(22)-C(38)), aldehydes (C(26) and C(28)), fatty acids (C(20)-C(34)) and triterpenoids (lupeol, beta- and alpha-amyrin). Besides, a series of n-alkane-1,3-diols was detected, with chain lengths ranging from C(22) to C(28), a strong predominance of even-numbered homologs, and a maximum for hexacosane-1,3-diol. Seven other compounds were assigned to a novel class of wax constituents and identified as homologous unbranched 3-hydroxyaldehydes ranging from C(22) to C(28). As the chain length distribution of this series closely paralleled the homolog pattern of 1,3-diols, it seems likely that both compound classes are biosynthetically related.     

Epicuticular waxes of two sorghum varieties

The epicuticular waxes of the two sorghum varieties Alliance A and SD 102 have been analyzed, after separation of the leaf blades from the sheaths. The major constituents were found to be free fatty acids but small amounts of esters, aldehydes, alcohols, n-alkanes and sterols were also detected. The typical chain lengths of aldehydes, free alcohols and free fatty acids were C₂₈ and C₃₀.     

Estradiol induces proliferation of peroxisome-like microbodies and the production of 3-hydroxy fatty acid diesters, the female pheromones, in the uropygial glands of male and female mallards

During the mating season the female mallards produce sex pheromones, diesters of 3-hydroxy fatty acids, in their uropygial glands. Subcellular fractionation by sucrose and Nycodenz density gradient centrifugations and electron microscopic examination of the fractions showed that diesters of 3-hydroxy acids and the enzymes that catalyze the formation and esterification of the 3-hydroxy fatty acids are located in the catalase-containing fractions, probably peroxisomes, whereas monoester synthesizing activities are located in the endoplasmic reticulum. Fatty acyl-CoA reductase that would provide fatty alcohol needed for the synthesis of monoester and diester waxes was found both in the peroxisomal and endoplasmic reticulum fraction. Upon daily intramuscular injection of estradiol into the females in the nonmating season, the short chain monoester waxes of the uropygial glands were replaced by long chain monoester waxes, and subsequently the monoester waxes were replaced by diester waxes. Injection of thyroxine with estradiol hastened the induction of the compositional changes including diester synthesis. Similar changes, including the synthesis of the female pheromones, were induced in the uropygial glands by the hormone treatment of males that do not normally produce diesters at any time during their life cycle. The structure and composition of the diesters induced by hormone treatment of both males and females were identical to those of the female pheromones produced during their mating season. Electron microscopic examination of diaminobenzidine-treated glands showed that peroxisomes proliferated in the gland of the females in the mating season and in the estradiol-treated males that produce the diesters.     

The chemical composition of uropygial gland secretions from ralliformes

The uropygial gland wax from rails contains ester waxes, triester waxes and triglycerides. The ester waxes are composed of mainly methyl-substituted fatty acids with predominantly n-alkanols. Methyl-branched alcohols are only found in minor amounts. The occurrence of 2,6,10- and 4,8,12-trimethyl-substituted acids can be used as chemotaxonomie markers. The triester waxes contain n-fatty acids, n-alkanols and alkyl-hydroxymalonic acids.     

Comparative study of the composition of waxes extracted from isolated leaf cuticles and from whole leaves of Citrus: Evidence for selective extraction

The effect of different extraction methods on the composition of samples of soluble cuticular lipids (SCL) of Citrus aurantium L. was investigated. The variation of extraction yields, when whole leaves were immersed in solvent, was studied as a function of solvent type and duration of immersion. Cuticular waxes were also quantitatively extracted from isolated cuticular membranes of C. aurantium and their composition was compared to that of samples obtained by the immersion method. Significant differences were observed. Higher carbon number homologues of the aliphatic constituent classes were discriminated against when whole C. aurantium leaves were extracted by immersion. The alkyl ester fraction was almost entirely lacking in extracts from whole leaves. The dependence on carbon chain length of the saturation concentrations in chloroform of major aliphatic SCL constituents was determined. The results are discussed in terms of the major physico-chemical processes involved in the extraction of SCL.     

Changes in leaf cuticular waxes of sesame (Sesamum indicum L.) plants exposed to water deficit

Sesame (Sesamum indicum L.) is one of the most important oilseed crops, having seeds and oil that are highly valued as a traditional health food. The objective of this study was to evaluate leaf cuticular wax constituents across a diverse selection of sesame cultivars, and the responses of these waxes to drought-induced wilting. Water-deficit was imposed on 18 sesame cultivars by withholding irrigation for 15d during the post-flowering stage, and the effect on seed yield and leaf waxes compared with a well-watered control. Leaf cuticular waxes were dominated by alkanes (59% of total wax), with aldehydes being the next-most abundant class. Compared to well-irrigated plants, drought treatment caused an increase in wax amount on most cultivars, with only three cultivars having a notable reduction. When expressed as an average across all cultivars, drought treatment caused a 30% increase in total wax amount, with a 34% increase in total alkanes, a 13% increase in aldehydes, and a 28% increase in the total of unknowns. In all cultivars, the major alkane constituents were the C27, C29, C31, C33, and C35 homologs, whereas the major aldehydes were the C30, C32, and C34 homologs, and drought exposure had only minor effects on the chain length distribution within these and other wax classes. Drought treatments caused a large decrease in seed yield per plant, but did not affect the mean weight of individual seeds, showing that sesame responds to post-flowering drought by reducing seed numbers, but not seed size. Seed yield was inversely correlated with the total wax amount (-0.466*), indicating that drought induction of leaf wax deposition does not contribute directly to seed set. Further studies are needed to elucidate the ecological role for induction of the alkane metabolic pathway by drought in regulating sesame plant survival and seed development in water-limiting environments.     

n-alkane profile of Argemone mexicana leaves

An n-hexane extract of fresh, mature leaves of Argemone mexicana (Papaveraceae), containing thin-layer epicuticular waxes, has been analysed for the first time by TLC, IR and GLC using standard hydrocarbons. Seventeen long-chain alkanes (n-C18 to n-C34) were identified and quantified. Nonacosane (n-C29) was established as the n-alkane with the highest amount, whilst octadecane (n-C19) was the least abundant component of the extracted wax fraction. The carbon preference index (CPI) calculated for the hydrocarbon sample with the chain lengths between C18 and C34 was 1.2469, showing an odd to even carbon number predominance.     

Role of very-long-chain fatty acids in plant development,when chain length does matter

Very long chain fatty acids (VLCFAs) are essential components for eukaryotes. They are elongated by the elongase complex in the endoplasmic reticulum and are incorporated into four major lipid pools (triacylglycerols, waxes, phospholipids, complex sphingolipids). Functional analysis of several components of the elongase complex demonstrated the essential role of VLCFAs in plants, invertebrates and vertebrates. Although VLCFAs changes in the triacylglycerol pool has no consequence for plant development, modifications of the nature and levels of VLCFAs in waxes, phospholipids and complex sphingolipids have, collectively, profound effects on embryo, leaf, root and flower development. VLCFAs levels in epicuticular waxes are critical for the regulation of epidermal fusions during organogenesis. VLCFAs phospholipids and sphingolipids are involved in membrane structure and dynamics regulating cell size but also division and differentiation. This review summarizes the recent findings in plants but also in other organisms, highlighting the importance of very long acyl chain length during development.     

Lipid composition of Cunninghamella elegans cultivated on n-alkanes]

The ability to oxidize n-alkanes was studied with various species of fungi belonging to the Cunninghamella genus. These fungi are able to assimilate hydrocarbons and to accumulate up to 1.5 g/litre of biomass. The most active strain was Cunninghamella elegans (-) 1204. The amount of lipids formed, and their composition, depended on the length of the carbon chain of oxidized alkane. The content of fat in the cells increased with the length of the hydrocarbon chain. The following lipid fractions have been detected: phospholipids, monoglycerides, diglycerides, triglycerides, sterols, free fatty acids, sterol esters, and hydrocarbons. The qualitative composition of the fractions depended, to a considerable extent, on the n-alkane utilized. Investigation of the fatty-acid composition of intracellular lipids has shown that fatty acids with an even number of carbon atoms are formed from hydrocarbons with an even number of these atoms, while fatty acids both with an even and odd number of carbon atoms are synthesized from hydrocarbons with an odd number of these atoms. The relative content of the acids with the same number of carbon atoms as that of the alkane being utilized increased with the length of the carbon chain.     

Epicuticular waxes of Panicum miliaceum,Panicum texanum and Setaria italica

Leaf waxes from Panicum miliaceum, P. texanum and Setaria italica have been analysed; the principal components are hydrocarbons, esters, al     

Moving beyond the ubiquitous: the diversity and biosynthesis of specialty compounds in plant cuticular waxes

Cuticular waxes coat aerial plant surfaces to protect tissues against biotic and abiotic stress. The waxes are complex mixtures of fatty-acid-derived lipids formed on modular biosynthetic pathways, with varying chain lengths and oxygen functional groups. The waxes of most plant species contain C₂₆–C₃₂ alcohols, aldehydes, alkanes, and fatty acids together with their alkyl esters, and comparisons between diverse wax mixtures have revealed matching chain length distributions between some of these compound classes. Based on such patterns, the biosynthetic pathways leading to the ubiquitous wax constituents were hypothesized early on, and most of these pathway hypotheses have since been confirmed by biochemical and molecular genetic studies in model species. However, the most abundant wax compounds on many species, including many important crop species, contain secondary functional groups and thus their biosynthesis differs at least in part from the ubiquitous wax compounds with which they co-occur. Here, we survey the chemical structures of these species-specific specialty wax compounds based on a comprehensive CAS SciFinder search and then review relevant reports on wax compositions to help develop and refine hypotheses for their biosynthesis. Across the plant kingdom, specialty wax compounds with one, two, and three secondary functional groups have been identified, with most studies focusing on Angiosperms. Where multiple specialty wax compounds were reported, they frequently occurred as homologous series and/or mixtures of isomers. Among these, it is now possible to recognize series of homologs with predominantly odd- or even-numbered chain lengths, and mixtures of isomers with functional groups on adjacent or on alternating carbon atoms. Using these characteristic molecular geometries of the co-occurring specialty compounds, they can be categorized and, based on the common structural patterns, mechanisms of biosynthesis may be predicted. It seems highly likely that mixtures of isomers with secondary functions on adjacent carbons arise from oxidation catalyzed by P450 enzymes, while mixtures of isomers with alternating group positions are formed by malonate condensation reactions mediated by polyketide synthase or ketoacyl-CoA synthase enzymes, or else by the head-to-head condensation of long-chain acyls. Though it is possible that some enzymes leading to ubiquitous compounds also participate in specialty wax compound biosynthesis, comparisons between co-occurring ubiquitous and specialty wax compounds strongly suggest that, at least in some species, dedicated specialty wax compound machinery exists. This seems particularly true for the diverse species in which specialty wax compounds, most notably nonacosan-10-ol, hentriacontan-16-one (palmitone), and very-long-chain β-diketones, accumulate to high concentrations.