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In this review, we provide an overview of the role of glucosinolates and other phytochemical compounds present in the Brassicaceae in relation to plant protection and human health. Current knowledge of the factors that influence phytochemical content and profile in the Brassicaceae is also summarized and multi-factorial approaches are briefly discussed. Variation in agronomic conditions (plant species, cultivar, developmental stage, plant organ, plant competition, fertilization, pH), season, climatic factors, water availability, light (intensity, quality, duration) and CO₂ are known to significantly affect content and profile of phytochemicals. Phytochemicals such as the glucosinolates and leaf surface waxes play an important role in interactions with pests and pathogens. Factors that affect production of phytochemicals are important when designing plant protection strategies that exploit these compounds to minimize crop damage caused by plant pests and pathogens. Brassicaceous plants are consumed increasingly for possible health benefits, for example, glucosinolate-derived effects on degenerative diseases such as cancer, cardiovascular and neurodegenerative diseases. Thus, factors influencing phytochemical content and profile in the production of brassicaceous plants are worth considering both for plant and human health. Even though it is known that factors that influence phytochemical content and profile may interact, studies of plant compounds were, until recently, restricted by methods allowing only a reductionistic approach. It is now possible to design multi-factorial experiments that simulate their combined effects. This will provide important information to ecologists, plant breeders and agronomists.

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Alkylresorcinols (ARs) are bioactive compounds occurring in many members of the Poaceae, likely at or near the surface of various organs. Here, we investigated AR localization within the cuticular wax layers of rye (Secale cereale) leaves. The total wax mixture from both sides of the leaves was found to contain primary alcohols (71%), alkyl esters (11%), aldehydes (5%), and small amounts (<3%) of alkanes, steroids, secondary alcohols, fatty acids and unknowns. A homologous series of ARs (3%) was identified by GC–MS and comparison with a synthetic standard of nonadecylresorcinol. The alkyl side chains of the wax ARs contained odd numbers of carbons ranging from C₁₉ to C₂₇, with a prevalence of C₂₁, C₂₃ and C₂₅. Waxes from both sides of the leaf, analyzed separately in a second experiment, comprised the same compound classes in similar relative amounts and with similar homolog patterns. Finally, the epicuticular and intracuticular wax layers were sampled separately from the abaxial side of the leaf. While ARs accounted for 2% of the intracuticular wax, they were not detectable in the epicuticular wax. The intracuticular wax was also slightly enriched in steroids, whereas the epicuticular layer contained more primary alcohols. All other wax constituents were distributed evenly between both wax layers.

▼ Caffeine and theobromine were identified and quantified in leaf epicuticular waxes of Ilex paraguariensis A. St.-Hil. (Aquifoliaceae). The total epicuticular leaf wax content was ca. 0.5% on average of dry leaf weight. Epicuticular caffeine and theobromine contents varied from 0.16 to 127.6 μg/mg and from 0 to 9.5 μg/mg of wax, respectively. For some selected samples, the intracellular methylxanthine concentration was also determined. A positive correlation was found between inner and epicuticular caffeine contents.

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Epicuticular waxes have been characterised from the flowers of raspberry and hawthorn, on both of which adult raspberry beetles (Byturus tomentosus) can feed. The flower wax from both species had similar alkane profiles and also contained long-chain alcohols, aldehydes and fatty acids. The range of the carbon numbers detected for these classes of compounds was broadly similar in both but the relative amounts of each differed between species. Raspberry flower wax also contained fatty acid methyl esters, a group of compounds that has rarely been detected in plant epicuticular waxes, however, these were not observed in hawthorn flower wax. Long-chain alcohol-fatty acid esters with carbon numbers ranging from C36 to C48 were also detected in both plant species. However, an examination of their constituent acids indicated that in hawthorn the esters based on the C16 fatty acid predominated, whilst in raspberry flower wax, esters based on the C20 fatty acid were most abundant. Both species also contained pentacyclic triterpenoids, which accounted for, on average, over 16 and 48% of the total wax extracted from raspberry and hawthorn flowers respectively. In the former, ursolic and oleanolic acids accounted for over 90% of the pentacyclic triterpenes, whilst hawthorn flower wax, in addition to containing these acids, also contained high relative concentrations of both free and esterified α- and β-amyrins.

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Epicuticular waxes from the aphid-resistant red raspberry (Rubus idaeus) cultivar Autumn Bliss and the aphid-susceptible cultivar Malling Jewel were collected from the newly emerging crown leaves, and also from the group of four more mature leaves immediately below the crown. Resistance and susceptibility status of the leaves to infestation by the large raspberry aphid, Amphorophora idaei, were determined by bioassay with the insect just prior to collection of the wax. Analysis showed the waxes to consist of a complex mixture of free fatty acids; free primary alcohols and their acetates; secondary alcohols; ketones; terpenoids including squalene, phytosterols, tocopherol and amyrins; alkanes and long chain alkyl and terpenyl esters. Compositional differences which may relate to A. idaei-resistance status were noticeably higher levels of sterols, particularly cycloartenol, together with the presence of branched alkanes, and an absence of C₂₉ ketones and the symmetrical C₂₉ secondary alcohol in wax from the resistant cultivar Bliss. There were also differences between the cultivars in the distribution of individual amyrins and tocopherols and in the chain length distribution for homologues of fatty acids, primary alcohols and alkanes, and these may also be related to resistance to A. idaei. Emerging leaves had lower levels of primary alcohols and terpenes, but higher levels of long-chain alkyl esters, and in general, more compounds of shorter chain-length than the more mature leaves. During bioassay A. idaei displayed a preference to settle on the more mature leaves. This may be due to greater wax coverage and higher levels of the compounds of shorter chain length found in the newly emerged younger leaves at the crown of the plant.

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Epicuticular waxes from two cultivars of red raspberry (Rubus idaeus) were collected from the newly emerging crown leaves, and also from the group of four more mature leaves immediately below the crown. One cultivar, Autumn Bliss, was identified as aphid-resistant, and the other, Malling Jewel, as aphid-susceptible following bioassay with the large raspberry aphid, Amphorophora idaei, just prior to collection of the wax. Biological activity was primarily associated with the more mature leaves. Epicuticular wax esters consisted predominantly of long-chain aliphatic compounds in which even-carbon-number acids were esterified to even-carbon-number alcohols. Lesser amounts of odd-carbon-number esters were also present. The acid : alcohol combinations of the major esters were C₃₈: 14 : 24, 16 : 22, 20 : 18; C₄₀: 14 : 26, 16 : 24, 18 : 22, 20 : 20; C₄₂: 16 : 26, 20 : 22; 22 : 20, C₄₄: 20 : 24, 22 : 22, 24 : 20; C₄₆: 20 : 26, 22 : 24, 24 : 22; C₄₈: 20 : 28, 22 : 26, 24 : 24, 26 : 22; C₅₀: 20 : 30, 22 : 28, 24 : 26, 26 : 24, 28 : 22 and C₅₂: 22 : 30, 24 : 28, 26 : 26. Terpenyl esters were also present and these consisted of α- and β-amyrin and cycloartenol esterified to C₁₆, C₁₈ and C₂₀ acids. Compositional differences between the more mature leaves which may relate to resistance to A. idaei were higher levels of cycloartenyl esters and α-amyryl esters in wax from the resistant cultivar Bliss. There were also differences between the cultivars in the distribution of individual alkyl esters and their component acids and alcohols. Esters with longer acid : shorter alcohol combinations were more abundant in Jewel than Bliss. There were compositional differences between leaves at the different developmental stages. Alkyl esters were more abundant and cycloartenyl esters were not detected in wax from the immature leaves. Small amounts of an unusual class of triacylglycerol were found only on leaves of the aphid-susceptible cultivar, Jewel, which had been subject to bioassay with raspberry aphid. These compounds, which have a C₆ acid at C-2 of the glycerol backbone, were derived from the aphid, and are the major component in the insect’s cornicle secretions. The triacylglycerols probably arise from the presence on the leaf surface of shed aphid skins, or by incorporation of cornicle fluid into the leaf wax. The abundance of aphid triacylglycerols on the leaf surface may provide a measure of aphid-susceptibility.

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It is known that branched-chain amino acids can serve as precursors to iso- and anteiso-branched components of epi-cuticular waxes. Keto acid deamination products of Val, Leu and Ile are thought to serve as primers which are elongated by fatty acid synthase. However, the origin of elongation carbons has not been studied directly. Nor has the mechanism for formation of odd-carbon-length, straight- or branched-chain, cuticular ester fatty acids or free odd-carbon-length, straight fatty acid components of waxes been characterized. It is not known that α-oxidation of even-length precursors or elongation of odd-length primers is involved in these cases. Here, we present evidence which substantiates the expectation that elongation of branched as well as straight-chain precursors to wax ester acids occurs by fatty acid synthase catalyzed by addition of two carbon units via acetate. Also, we present evidence which indicates that odd-carbon-length acids can result from elongation of odd-carbon-length primers (at least branched), rather than even-length acids shortened by α-oxidation.

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The composition of intact leaf epicuticular wax esters of two individual genotypes each of kale and swede grown indoors (I) and outdoors (O) at SCRI, Scotland, and outdoors at Wädenswil in Switzerland (S), were determined by GC-mass spectrometry. For all genotypes (I, O, S) esters were found to consist of unbranched (n-) and branched anteiso- (a-) and iso- (i-) components in the a:a, a:i, i:a, a:n, n:a, n:n and i/n:n/i acid-alcohol combinations. Esterification was non-random, n:n and doubly branched br-/br- combinations were favoured over mixed n-/br- combinations. Combinations with extremes of acid and alcohol chain-length were generally uncommon, although longer-chain alcohols were more predominant in some swede esters. There were considerable compositional differences between indoor-grown plants (I) and those grown outdoors (O and S). In general, i:n/n:i, i:a and a:i esters were relatively more abundant in (O and S) and n:n and n:a esters were more abundant in (I), whereas a:n and a:a esters were of similar abundance in all (I, O and S). Generally, (I)-grown plants were found to have proportionally more esters of longer chain-length and (O, S)-grown plants proportionally more esters of shorter chain-length. For kale a:a, n:n, a:n and n:a esters, this was particularly related to variation in alcohol chain-length. There were also major compositional differences between kale and swede esters, long-acid-short-alcohol combinations were more prominent in the former, while short-acid-long-alcohol combinations dominated in the latter.

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Quantification of the epicuticular wax from the stems of 40 ecotypes of Arabidopsis thaliana showed a two-fold range in total wax load that was not correlated to known abiotic characteristics of the ecotype's origin of collection. Chemical analysis of these ecotypes revealed similar epicuticular wax profiles for all ecotypes except CT-1. In CT-1 the amount of 22 and 24 carbon length primary alcohols was increased by 16- and 8-fold, respectively, over that observed in the epicuticular wax averaged over all ecotypes.

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The 5-(n)-alkylresorcinol fraction of the epicuticular waxes of Hordeum vulgare seeds appeared to be responsible for their in-born resistance to pathogenic fungi such as Aspergillus niger and Penicillium crysogenum. The antifungal properties of this fraction were evaluated qualitatively and quantitatively with a novel bioassay where the extreme lipophilicity of these compounds was taken into account. The minimum inhibitory concentration in the fungi tested ranged from 5.6 to 10 μg cm⁻² for the alkyresorcinols. The behaviour of the different cultivars against these fungi could be predicted by measuring the natural amount of resorcinols of each variety by TLC-scanning densitometry. The ranking of cultivars thus established correlated well with the field behaviour of each cultivar, providing a useful and rapid method for predicting the behaviour against fungi of new varieties being developed.

▼ Compounds of four chemical classes (alkanes, primary alcohols, free fatty acids and polar lipids) were isolated, identified and quantified for the first time from the epicuticular waxes of Prunus laurocerasus leaves. Alkanes were the major class and constituted 80% of the wax. Using chloroform, more wax was removed from leaves after dipping for 210 sec than by rinsing for the same length of time. Duration of solvent contact also had an effect on the composition of the soluble cuticular lipids extracted. Alkanes and primary alcohols were extracted earlier than fatty acids and, whatever the class of compounds, short chain-length homologues (C₁₆ C₂₅) needed more time to be extracted from the cuticle than longer ones (C₂₆ C^3^5).

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The epicuticular leaf waxes from four glaucous and four non-glaucous species of Encephalartos were examined by GC-mass spectrometry and SEM techniques. The four glaucous-leaved species, E. horridus, E. lehmannii, E. princeps and E. trispinosus, all occurring in xeric conditions in the Eastern Cape Province of South Africa, were conspicuous in having leaf waxes containing a series of secondary alcohols. In addition to 10-nonacosanol as the principal wax component, minor amounts of C₂₅-C₃₁ 10-alkanols, 4,10-, 5,10- and 7,10-nonacosanediol and the ketone, 10-nonacosanone, were detected in these species. The adaxial leaflet surfaces of the glaucous species all showed a distinctive trabecular deposit of wax platelets when viewed microscopically. By contrast, secondary alcohols and ketones were absent in waxes from the non-glaucous species, and the surface of leaflets of these taxa were relatively featureless microscopically. Varying quantities of alkanes, fatty acids, primary alcohols, aldehydes and alkyl esters were present in all samples. Amongst the non-glaucous species, E. altensteinii, E. natalensis and E. woodii were similar in their wax composition, but differed from E. villosus. Alkanes were dominant in the latter species, which had high proportions of hentriacontane and tritriacontane in parallel with the most prominent oxygenated wax compounds, C₃₂ and C₃₄ fatty acids and aldehydes.

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We analysed the leaf epicuticular wax chemical constituents on wildtype and eceriferum (cer; cer1,cer 3 and cer4) mutants of Arabidopsis thaliana at 7, 15, 25 and 40 days after germination. Changes during development are described for the partitioning of epicuticular waxes into the five major chemical classes; free carboxylic fatty acids, aldehydes, alkanes, primary alcohols and wax esters. Changes are described for cumulative total epicuticular wax loads per leaf area, percentages of total constituents in each of the five major chemical classes and chain length distributions for the two major chemical classes: alkanes and primary alcohols. Stem epicuticular waxes on wildtype and cer mutants were analysed at 25 and 40 days and found to be similar.

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The epicuticular leaf waxes of nine willow clones (one Salix myrsinifolia, four Salix dasyclados, one Salix hybrid and three Salix viminalis clones) with different overwintering survival rates and biomass productivities were analysed by combined gas chromatography-mass spectrometry. The waxes were composed of n-alkanes (C₂₁-C₃₁), long-chain aliphatic esters (C₃₆-C₅₈), n-alcohols (C₂₀-C₃₀), n-aldehydes (C₂₄-C₃₀) and saturated free fatty acids (C₁₆-C₃₀). Two types of waxes were observed. The S. viminalis clones had n-alkanes as their major wax component and n-docosanol as their major n-alcohol, whereas the other clones contained approximately equal proportions ofn -alkanes, free fatty acids, n-alcohol and n-aldehydes and had n-hexacosanol as their majorn -alcohol. The total epicuticular leaf wax contents varied from 3 μg cm⁻² to 24.9 μg cm⁻² and epicuticular n-alkane contents from 0.7 μg cm⁻² to 14.8 μg cm⁻². A correlation between high wax content, high n-alkane content, two overwintering survival and high biomass productivity of the clones was observed.

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The composition of leaf epicuticular waxes of two genotypes each of kale and swede were determined by gas chromatography-mass spectrometry. Plants were grown indoors (I) and outdoors (O) at SCRI, Scotland, and outdoors at Wädenswil in Switzerland (S). Epicuticular waxes from outdoor-grown plants (O and S) were found to have higher proportions of n-alkanes, octacosanoic acid, primary alcohols and long-chain esters but lower proportions of aldehydes, ketones, ketols and secondary alcohols than waxes from (I)-grown plants. Outdoor-grown plants were also found to have proportionally more shorter chain length compounds and indoor-grown plants proportionally more compounds of longer chain length. Variations in wax composition between genotypes of a species and between species were also observed. Differences in leaf surface wax ultrastructure, between species, and between different growth conditions were detected using scanning electron microscopy. The possible role of leaf wax chemicals in the antixenotic resistance to the turnip root fly, Delia floralis, of certain genotypes was also considered.

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The leaf wax characteristics of Dryas octopetala and Saxifraga oppositifolia, collected from the high Arctic semi-desert of Svalbard, Norway (79° N, 13° E), were compared and differences in their wax composition related to winter snow cover. The leaf wax composition of the winter-green D. octopetala differed from that of the herbaceous S. oppositifolia in that high abundances of the triterpenoids, ursolic acid, oleanoic acid and uvaol, were observed in D. octopetala extracts but not in S. oppositifolia extracts. D. octopetala leaf waxes were consistently lower inn -alkanes and in n-alkanols compared to the leaf waxes of S. oppositifolia. Leaf waxes of both species from snow-free, wind-swept microsites had significantly higher abundances of n-alkanes than in those plants growing in adjacent, swale areas where snow accumulates in winter. It is hypothesized that this higher abundance of n-alkanes may be due to a response to a greater degree of dessication, lower temperatures and lower soil moisture experienced by plants on the snow-free ridge microsites during leaf expansion. In order to test whether these biochemical and anatomical attributes might change in response to short term alterations in winter climate, snow fences were erected on ridge sites. The wax attributes of ridge plants exposed to a single year of increased winter snow cover were examined and the n-alkane composition of leaf waxes were observed to be more like those of plants growing in adjacent swale areas than for those of ridge plants growing in unmanipulated areas. This shift in leaf wax composition implies that environmental differences during leaf development can have an influence on final leaf wax composition.

▼ Epicuticular waxes from 55 plants of the seven species of Sedum series Rupestria and four artificial hybrids have been examined by GC and GC-MS. The taxa were S. amplexicaule, S. forsterianum, S. montanum ssp. montanum, S. montanum ssp. orientale, S. ochroleucum, S. pruinatum, S. rupestre ssp. erectum, S. rupestre ssp. rupestre, S. sediforme, and four hybrids between S. forsterianum and S. rupestre ssp. erectum. Alkanes, alcohols, aldehydes, triterpenoids and wax esters were the main wax components. Comparison of wax composition and wax ultrastructure of glaucous and glossy plants led to the conclusion that triterpenoids are primarily responsible for glaucousness. Some 14 triterpenes were detected, the major being germanicyl formate, fern-8-en-3-yl formate, taraxerone and taraxeryl acetate. Fern-8-en-3-yl formate was isolated from S. forsterianum. The distribution of triterpenes generally supported the phylogeny of the species based on a combination of biosystematic and molecular data, but failed to provide additional evidence for the presumed allopolyploid origin of S. rupestre ssp. rupestre from S. forsterianum and S. rupestre ssp. erectum.

▼ Epicuticular waxes from 30 species of Sedum and 2 species of Sempervivoideae, i.e. Aeonium spathulatum and Sempervivum nevadense, have been analysed by GC and GC-MS. The Sedum taxa examined were S. acre, S. album, S. series Alpestria (13 species), S. anglicum, S. brevifolium, S. litoreum, S. lydium, S. series Macaronesia (four species), S. melanantherum and S. series Rupestria (five species) of S. sect. Sedum and S. meyeri-johannis of S. sect. Africana. The waxes consist of alkanes, alkanols, fatty acids, fatty acid methyl esters, aldehydes, wax esters and triterpenes. Some 14 triterpenes were detected in waxes of Sedum, the major triterpenes being β-amyrenyl acetate, germanicyl formate (not previously reported from a natural source), multiflorenyl acetate and taraxeryl acetate. Waxes of the pruinose and glaucous taxa of Sedum were found to have a high triterpene content. In waxes of Aeonium spathulatum and Sempervivum nevadense, no triterpenes could be detected. Variation in the alkane and triterpene profiles proved to be of significant systematic value. In general, the distribution of the triterpenes in Sedum agrees with the infrageneric classification based on hybridization patterns and related morphological characters.

▼ The principal surface lipids of Arabidopsis are n-nonacosane, 14- and 15-nonacosanol, 15-nonacosanone, C₁₆-C₃₀ free fatty acids, C₂₆-C₃₀ primary alcohols and C₂₆-C₃₀ aldehydes. We have analysed the chemical composition of the epicuticular wax of 10 Arabidopsis thaliana eceriferum (cer) mutants. One of the mutants (cer2) is blocked in the elongation of octacosanoic acid and accumulates large amounts of primary alcohols and fatty acids in its epicuticular wax. The surface lipid composition of another mutant (cer4) appears to be defective in the production of primary alcohols and accumulates elevated levels of epicuticular alkanes. We have also identified a mutant (cer1) which accumulates epicuticular aldehydes and is severely deficient in alkanes on its surface. Seven other mutants had only slightly different epicuticular wax compositions compared to those of wild type plants.

▼ The n-alkane distribution patterns from 31 specimens in the meso-American cycad genera Ceratozamia, Dioon, Zamia and two Australian taxa, reported from GC analysis, complement a previously published investigation of the African genus, Encephalartos and complete a survey of the Zamiaceae. The significant proportions of n-alkane homologues with short (<n-C₂₅) carbon chains, the extended distribution range (n-C₂₆ to n-C₃₃) and a general absence of prevalence of odd- over even-numbered homologues collectively provides evidence for a monophyletic origin of the Zamiaceae and distinguishes the cycads chemotaxonomically from other gymnosperms and from angiosperms. Exceptions to the general trend are seen in Dioon califanoi, which shows an angiosperm-like bias towards odd-numbered carbon alkanes, and to a lesser extent in two species of Ceratozamia and three of Zamia. Alkane distribution profiles do not allow any distinction between the genera of the Zamiaceae and show little species specificity.

▼ The main components of the chloroform-soluble epicuticular waxes from olive tree leaves (Olea europaea cvs Coratina and Cipressino), were triterpene oleanolic and betulinic acids and triterpenols sitosterol, α- and β-amyrin, uvaol and erythrodiol. The waxes of both cultivars contain the ubiquitous wax classes of alkanes, alcohols, aldehydes, fatty acids and alkyl esters. Methyl phenyl esters and 2-phenyl-ethanol-1-esters were both present in low amounts in cv. Coratina whilst cv. Cipressino contained only the former class of compounds. Furthermore cv. Coratina contained triacylglycerols that were missing in cv. Cipressino wax.

▼ The chloroform-soluble waxes of green and black olive fruits (Olea europaea cv Coratina) contain alkanes (C₂₃-C₃₃), saturated and unsaturated alkyl esters (C₃₈-C₅₆), aldehydes (C₂₄-C₃₀), methyl phenyl esters, triacylglycerols, alcohols (C₂₂-C₂₈), fatty acids (C₁₆-C₂₈), and pentacyclic triterpenols and triterpenoid acids. Oleanolic acid and triacylglycerols are the major components. Uvaol and erythrodiol, present in substantial amount in wax from green olives, were present only in trace amounts in that from black olives.

▼ The epicuticular waxes of Tilia tomentosa were analysed continuously over one vegetation period. The rolled leaves in buds contain waxes quite different in composition from those of mature leaves. Waxes of very young unfolded leaves are composed of homologous series of hydrocarbons, alkyl esters, triterpenol esters, acetates, alcohols, fatty acids and α- and β-amyrin. After 15 days of leaf unfolding, the biosynthesis of β-amyrenyl acetate and later on aldehydes commenced. A rapid biosynthesis of epicuticular waxes was observed from April to June. Wax content doubled or tripled in that time. An increasing trend was found for the synthesis of hydrocarbons, aldehydes, alcohols, fatty acids, β-amyrin and β-amyrenyl acetate during the active biosynthetic phase. The synthesis of wax esters and acetates, however, had almost stopped after the unfolding of leaves. During leaf development β-amyrenyl acetate became the dominant epicuticular wax component comprising ca 44% of the wax. From July to November the wax amount and composition remained nearly constant.

▼ Chemical compositions of waxes from modern corn and its putative ancestors, annual teosinte (Zea mays subsp. mexicana and subsp. parviglumis) and diploid perennial teosinte (Z. diploperennis) are reported. The common components are alkanes, esters, aldehydes, alcohols and acids. Comparison is also made with waxes from Coix lachryma, a species from a genus distantly related to modern corn. The diploid perennial teosinte shows a distinct profile of surface lipids, in which alcohols are present at lower concentrations. The major homologue of alcohols and aldehydes is C₃₂. Alkanes chain lengths provide a criterion to classify the related species into different groups. The C₃₃ homologue is present in unusual high amounts in teosintes, whereas odd and even alkanes characterize Coix waxes. Ontogenic variations are also observed in homologue composition. In general, alkane chain lengthening is associated with chain length shortening of aldehydes and alcohols.

▼ Wax components of the aerial parts of mature plants of Sorghum bicolor were compared with those from the panicles and mature grains. Lipid content of the grain flour was also analysed. Attention has been paid to the polycyclic triterpenes distributions comparing different varieties of sorghum. The general occurrence of hopanoids suggests that they are significant chemotaxonomic markers for S. bicolor. Dotriacantanol was found to characterize the lipid content of the grain flour. Observations on this finding are reported.

▼ The structural composition is reported of epicuticular wax esters from maize. The waxes from wild type (Gl) plants at different stages of growth and those from some glossy (gl) seedlings and an albino strain of maize have been analysed for their content of esters. Influence of age and mutations on the epicuticular wax ester composition is discussed.

▼ The n-alkane distribution patterns in the epicuticular leaf wax of 42 taxa of Encephalartos, a major genus of Cycadales, are reported from GC analyses. Three chemical groups are identified. Group A has well-defined maxima for the odd carbon atom numbered alkanes n-C₂₉,and n-C31 and n-C33, a distribution commonly reported from higher plants. Group B shows a skewed normal n-alkane profile centred around n-C₂₀, while Group C has a bimodal n-C₂₀/n-C_25-31 pattern. The latter two groupings are atypical for higher plants and are tentatively explained in terms of an α-oxidation process in the usual elongation-decarboxylation biosynthetic route. The chemical groups are not obviously correlated with the existing taxonomy of the genus. Mature leaves from seedling plants show similar n-alkane profiles to those of older plants of the same species.

▼ One hundred and ten species of Velloziaceae were surveyed for the distribution of the alkanes in their foliar epicuticular waxes. Longer chains were found in waxes of representatives of subfamily Barbacenioideae, the main homologues being mostly n-C₃₃ or n-C₃₅ except most members of Pleurostima, which had n-C₃₁ or n-C₃₃ the main alkane. In Vellozioideae, the main alkane was chiefly n-C₂₉. The results support proposals for the establishment of Burlemarxia and the re-establishment of Pleurostima, but does not lend support to the recognition of Brazilian Xerophyta as distinct from Vellozia and of Aylthonia as distinct from Barbacenia. In some cases very small or no differences were noted among the alkane profiles of different specimens of the same species, but in other cases substantial differences were detected.

▼ Interspecific variation in 19 species of Chionochloa was investigated by examining the major carbon chain lengths of fatty acids, alcohols, aldehydes, wax esters and alkanes of the epicuticular waxes. The chain lengths ranged from C₂₄ to C₃₂ in the acids, alcohol and aldehydes C₂₁ to C₃₃ in the alkanes and C₃₄ to C₅₂ in the wax esters. The degree of similarity between samples in terms of chain length distribution in the various lipid classes was calculated. In general, each sample has its own characteristic sequence of groups in the sequence order acid, alkane, alcohol, aldehyde and ester. Using this sequence, it is possible to identify a species of Chionochloa if its original locality is known. Complete analysis of the major chain lengths of all five lipid fractions demonstrated the chemotaxonomic inter-relationship between the 19 species of Chionochloa. One Australian species, C. frigida, was chemically similar to some of the New Zealand species.

▼ Epicuticular wax from Abies balsamea contains methyl esters (7%), hexyl and octyl esters (9%), nonacosan-10-ol (14%), free acids (20%), diterpene acids (3%) and free acids and diols (2%) and wax from Picea glauca has methyl esters (6%), hexyl and octyl esters (5%), aldehydes (3%), nonacosan-10-ol (30%), free acids (3%), diterpene acids (10%) and free alcohols and diols (2%). The major methyl ester is methyl triacontanoate; the long-chain esters are C₃₀ C₄₄ hexyl and octyl esters of C₂₄ C₃₄ acids; the major aldehyde is triacontanal. Major free acids and alcohols are C₁₆ C₃₂ and the principal diol is nonacosane-5,10-diol.