Epicuticular wax structures on stems and comparison between stems and leaves – A survey

The cuticle, forming the outermost layer of plant tissues and being in direct contact with the environment, consists of waxes and cutin. Waxes are hydrophobic substances that are divided in two groups: intra- and epicuticular, depending on their localisation. Epicuticular waxes appear as smooth coverings, however, many plants also produce superimposed wax structures of a crystalline nature. While studies of waxes have almost exclusively focused on leaves, here a survey of epicuticular wax structures on stems is presented. The stem surface of 343 higher plant taxa, representing 80 families, was examined using scanning electron microscopy. The adaxial and abaxial surfaces of leaves of 319 taxa were also examined to determine the relationship between wax structures on stems and leaves. Wax structures are classified, described and discussed. The results of the study indicate that stems exhibit the same main wax crystal types that have been described for leaves. Seventy percent of the examined taxa produced wax crystals on their stems. In ∼24% of the taxa, wax crystals were absent on leaves and found only on stems. In plant taxa that produce wax crystals, 40% exhibit the same type on either side of their leaves and on their stem. However, a much stronger morphological similarity exists between crystal shapes present on the adaxial and abaxial surfaces of leaves than between those present on the stem and those on leaves. In general, these observations suggest that stems are quite different than leaves in terms of their epicuticular wax structures.     

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

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

Surface wax, a new taxonomic feature in Plagiochilaceae

A scanning electron microscope study of 81 species of Plagiochilaceae revealed the presence of superficial waxes on the leaves and stems ofPlagiochilion mayebarae and 5 species ofPlagiochila. The waxes are not visible in the light microscope and were unknown in Plagiochilaceae.Plagiochila fuscolutea andP. longiramea (=P. sect.Fuscoluteae) are characterised by the predominant occurrence of membraneous wax platelets;Plagiochila aerea, P. rudischusteri andP. tabinensis(=P. sect.Bursatae) predominately form various types of wax rodlets. Our findings show for the first time the systematic usefulness of leaf surface waxes in the liverworts.P. tabinensis contains surface waxes in amounts of ca. 1.4% dry weight composing of steryl esters, triacylglycerols and free fatty acids.     

Attachment ability of the beetle Chrysolina fastuosa on various plant surfaces

To study the role of different structures of a plant surface preventing insect attachment, a variety of plant surfaces were screened. Attachment ability of the beetle Chrysolina fastuosa Scop. (Coleoptera, Chrysomelidae) was measured on 99 surfaces among them smooth, hairy, felt-like, waxy, and glandular ones of three plant organs (stems, leaves, fruits) of 83 plant species belonging to 45 families. Insects attached successfully to smooth, hairy, and felt-like substrata. These surface types did not effect the further attachment of C. fastuosa, indicating the adhesive system remained intact after contacting these substrata. However, the beetles could not attach properly to surfaces covered with wax crystalloids or glandular hairs. In most experiments on pruinose plant substrata, no influence of the surfaces on the subsequent attachment ability of insects was observed. Only in one case (the stem of Acer negundo), was such an impairment recorded, but recovery of attachment ability was fast. Crystalloids of this plant species probably temporarily disable function of tenent setae of C. fastuosa. Four hypotheses, explaining anti-adhesive properties of plant surfaces, covered with wax crystalloids are proposed. A plant surface with glandular trichomes disabled the attachment system of the beetle for a long time. Secretions of trichomes probably glue tenent setae together making further attachment impossible.     

Comparative anatomy of leaves and stems in some species of the South American genus Chrysolaena (Vernonieae,Asteraceae) and taxonomic implications

Vegetative anatomical features are poorly known in the South American genus Chrysolaena. In this study, leaves and stems of six Chrysolaena species were described and compared morphologically and anatomically using diaphanization, microtome serial sectioning and scanning electron microscopy. The species differed in leaf epidermis, type of stomata, shape of anticlinal walls of epidermal cells, trichome density, and presence or absence in stems of small air spaces in the cortical parenchyma and of druse‐shaped oxalate crystals. Furthermore, glandular trichomes and three types of non‐glandular trichomes with different number of basal cells were identified on leaves and stems. Collectively, these features proved instrumental to discriminate among the six studied species, suggesting that leaves and stems of Chrysolaena can represent a source for taxonomically useful characters. We also discuss anatomical features in relation to the environmental conditions in the species’ habitats.     

植物角质层内外蜡质的差异及其与抗逆性的关系

植物角质层是覆盖在植物地上部分的叶、花和非木质茎等器官表面的保护层,包括角质和蜡质。其中蜡质根据分布位置不同又分为表皮蜡质和内部蜡质。大量研究表明,表皮蜡质含量和结构在植物生长发育和抗逆性申发挥着重要作用。近年来有研究发现构成蜡质的成分在内外蜡质层中的分布存在差异,角质层蜡质成分影响植物抗逆性。本文针对角质层结构和内外蜡质差异性以及角质层结构和组成与植物抗逆性之间的关系进行了综述。     

植物蜡质及其与环境的关系

陆生植物的地上部分如叶、茎、花、果实等的表面覆盖着一层蜡质,它是由一系列复杂化合物组成的具有三维微结构的疏水层,在植物生长和发育过程中起着不可或缺的作用,具有很好的生物学功能。作为植物与环境的第一接触面,蜡质对外界环境因子的响应较敏感,当植物受到外界不利环境因子胁迫时,蜡质会改变自身晶体结构形态或化学组分构建防御机制以减少胁迫因子的作用,有效地协调植物与环境的关系。综述了近年来国内外关于植物蜡质的研究进展,在阐述蜡质层结构及其化学组分的基础上,着重介绍植物与环境因子的作用,包括非生物环境因子如水分、温度、光照、环境污染等以及植食性昆虫和病原菌等生物环境因子的作用。研究显示,胁迫环境下植物蜡质化学组分的变化,是由于不利环境因子的作用足以改变蜡质各产物的合成途径,从而影响蜡质产物。植物蜡质利用各种生理、化学机制对胁迫环境因子的适应以及响应,是植物适应各种生境的基础,因此通过对植物蜡质与环境关系的研究为进一步解析植物与环境关系提供证据。     

Fungal endophytes associated with the mistletoe <Emphasis Type="Italic">Phoradendron perrottettii</Emphasis> and its host tree <Emphasis Type="Italic">Tapirira guianensis</Emphasis>

The endophytic mycobiota of leaves and stems of the mistletoe Phoradendron perrottettii and its host tree Tapirira guianensis, two physiologically connected plant species of the Brazilian savannah in southeastern Brazil, were investigated to evaluate host and organ recurrence among endophytes. Leaves and stems of P. perrottettii and leaves of T. guianensis were sampled in the dry and wet season. Stems of T. guianensis were also sampled in the wet season. Endophytes were isolated by an adapted trituration and particle filtration protocol. A total of 1,615 isolates representing 99 species and 20 sterile morphotypes were recovered; 64 morphospecies occurred as singletons. The number of isolates and species was higher in the wet season. Leaves of P. perrottettii were less densely colonized than other organs studied, but were the most species-rich. Conversely, stems of T. guianensis yielded more isolates but were less species-rich. Both plants were found to harbor similar but distinguishable endophytic assemblages. The Jaccard’s index of similarity between the fungal assemblages of both plants was 0.82, higher than found for other plants in similar habitats. The fungal species composition seemed to be influenced by the collection season and organ type, as demonstrated by multivariate correspondence analysis. Paraconiothyrium brasiliense, P. sporulosum and Verticillium leptobactrum were the dominant species in P. perrottettii. In leaves of T. guianensis, Pseudocercospora sp., Phomopsis sp. 1 and Lecanicillium psalliotae were the most frequent, while Stagonospora sp. 1 and Phomopsis sp. 1 were the dominant endophytes in its stems. The results indicated that some of the dominant endophytic taxa isolated in this study colonize different hosts and plant organs while others seem to exhibit a high degree of host or organ recurrence. This study represents the first evaluation of diversity of fungal endophytes in natural vegetation of the Brazilian savannah and contributes information about the distribution and possible specificity of endophytes in tropical dicotyledoneous plants.     

Leaf Epidermal Microfeatures of 28 Salix Species under Scanning Electronic Microscope and Their Taxonomical Significances

In this paper, twenty eight species of the genus Salix, with similar phenotypic characters, were selected to study the leaf epidermal microfeatures under Scanning Electronic Microscope (SEM). Seven types of wax layer are totally detected in those species, including smooth layer, crust, fissured layer, non entire platelets, membraneous platelets, conicoids and scale like conicoids. Among those types, conicoids and scale like conicoids are exclusively found in Salix, while non entire platelets and membraneous platelets in Salix are depicted for the first time. The microfeatures of leaf hairs of Salix plants under SEM are less diversified than their macrofeatures, with detectable microfeature variations on hair length, density and degree of curve (straight, slightly curved and deeply curved). In conclusion, our results showed leaf epidermal microfeatures of wax layer types and stomatal apparatus are relatively unchangeable, which are valuable in the discrimination of similar Salix species. The Salix species from colder region and/or higher elevation usually bear diverse microfeatures, which might be adaptive evolution to colder environments.     

Seasonal responses of avian communities to invasive bush honeysuckles (<Emphasis Type="Italic">Lonicera</Emphasis> spp.)

Invasive bush honeysuckles, Lonicera spp., are widely viewed as undesirable; however, the effects of Lonicera spp. on native fauna are largely unknown. We investigated how breeding and overwintering bird communities respond to the presence of Lonicera spp. by comparing communities in forested areas with Lonicera spp. to those with a native shrub understory. The dense understory created by Lonicera spp. was associated with a change in the breeding bird community. We found large increases in the densities of understory bird species (e.g. northern cardinals) and decreases in select canopy species (e.g. eastern wood-pewees) in Lonicera spp. sites. In winter, we observed greater densities of frugivorous birds (e.g. American robins) likely due to the fruits that remain on Lonicera spp.; however, there was no difference in the community composition between sites with and without Lonicera spp. Given the widespread distribution of Lonicera spp., this invasive species may facilitate the population increase and range expansion of selected bird species. Many bird species appear to utilize Lonicera spp. for nesting and foraging; therefore, its removal should be accompanied by restoring native shrubs that provide needed resources.     

28种柳属植物的叶表皮微形态特征及其分类学意义

对28种表型相似、种间界限模糊的柳属植物在扫描电子显微镜下的叶表皮微形态特征进行观察,结果表明:柳属中有7种角质层蜡质纹饰,分别是平滑蜡质层、壳状蜡质层、痂状蜡质层、片状晶体、膜片状晶体、锥形纤维体和鳞片状纤维体,其中锥形纤维体和鳞片状纤维体为柳属所特有,而片状晶体和膜片状晶体为首次在柳属植物中发现;扫描电子显微镜下柳属植物叶表皮毛被的微观形态特征并不似其宏观形态(疏毛、绢毛、绒毛等)那样具有显著差异,微观形态主要表现为毛被密度、长短和卷曲方式(分为直,微弯曲和深度卷曲三种)的不同.研究表明叶表皮蜡质纹饰类型、气孔器的形态等微形态特征较为稳定,对柳属植物中表型相似的种类有很好的鉴定价值,但对组、亚属水平的界定作用不大;分布于寒冷地区和高海拔地区的柳属植物的叶表皮微形态特征相对多样,这可能是植物对寒冷环境的适应进化.     

Fruit quantity of invasive shrubs predicts the abundance of common native avian frugivores in central Pennsylvania

Aim Biological invasions pose one of the most severe threats to global biodiversity. Still, invasions can create positive ecological relationships and services, which can sometimes result in challenges for conservation efforts. A case in point is the invasion of alien plants that form mutualisms with native frugivorous birds. Here, we examined the correlation between honeysuckles (Lonicera spp.) and the bird communities in a landscape of central Pennsylvania during the fall months. Location State College area in central Pennsylvania, USA. Methods We conducted point counts to quantify the abundance of birds and fleshy‐fruited plant species within a 187.5 km² landscape that included forested, urban and agricultural lands. We also compared fruit‐removal rates for a native fruiting plant under low and high Lonicera densities. Results The abundance of birds showed a strong positive association with Lonicera fruits, with the abundance of Turdus migratorius and Dumetella carolinensis showing the strongest correlations. We also found that fruit‐removal rates were 30% larger for a native plant species in areas of high Lonicera density compared to a site with low density of Lonicera. Main conclusions Our results suggest that Lonicera may currently serve as a main axis for the organization of bird communities and the networks of frugivore–plant interactions in central Pennsylvania. Since populations of key bird frugivores may be currently depending on Lonicera resources, we argue that control measures should account for the negative effects that the loss of this fruit resource could have on populations of native consumers in highly invaded regions.     

Action of ultraviolet radiation (UV-B) upon cuticular waxes in some crop plants

The surface structure and composition of surface lipids were examined in leaves of barley, bean, and cucumber seedlings grown in a growth chamber under white light and low levels of ultraviolet (UV-B; 280–320 nm) radiation. The cuticular wax of cucumber cotyledons and bean leaves appeared as a thin homogeneous layer, whereas on barley leaves crystal-like structures could be observed under these irradiation conditions. Principally, the amount of cuticular wax found in barley leaves was five times greater than in bean or cucumber leaves. The prediominant wax components were primary alcohols in barley, primary alcohols and monoesters in bean, and alkanes in cucumber cotyledons. Irradiation with enhanced UV-B levels caused an increase of total wax by about 25% in all plant species investigated. Aldehydes, detected as a minor constituent of cucumber and barley wax, increased twofold. Distribution patterns of the homologs within some wax classes were different at low and enhanced UV-B levels. In general, the distribution of the homologs was shifted to shorter acyl chain lengths in wax of leaves exposed to enhanced UV-B levels. This was most apparent in cucumber wax, less in bean or barley wax. The UV-B-caused effects upon cucumber wax were mainly due to a response by the adaxial surface of the leaf.Abbreviation UV-B Ultraviolet radiation (280–320 nm)     

Die Wasserbenetzbarkeit von Blattoberflächen und ihre submikroskopische Wachsstruktur

Summary The wettability of a leaf surface is defined by the contact angle between a water-droplet and the surface of the leaf.Contact angles of 60–80° were measured on easily wettable leaves. These leaves have no wax on the outer cuticular layer.Contact angles of 130–160° were measured on leaves with a low wettability. These leaves have wax on the outer cuticular layer, which shows submicroscopic structures characteristic of the particular plants.A comparison of the wettability and the different structures of the wax showed no true distinctions.The wax does not adhere strongly to the outer cuticular layer and is cast off in the case of old leaves. Therefore the wetability alters with the age of the leaves. If the wax on young leaves is destroyed or removed by outer influences it can be produced again within a few hours.The rebuilt structure of the wax is not always similar to the original one. When the wax was dissolved by organic solvents no new wax formation was observed.Cigarette smoke greatly increases the wettability of leaves of Tropaeolum majus, parochetus communis and Chelidonium majus without causing a visible alteration of the submicroscopic structure. In this case the leaves recover their water-repellency within a few hours, but not if they were treated with Diesel smoke.When the wax structure was destroyed by fungus or Aleurodina no new wax formation was observed.

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Herrn Professor Dr. Walter Rentschler zum 60. Geburtstag     

In vitro Reconstitution of Epicuticular Wax Crystals: Formation of Tubular Aggregates by Long-Chain Secondary Alkanediols

Cuticles of several plant species are covered by tubular wax aggregates that are known to consist mainly of (S)-nonacosan-10-ol. The present work addresses the question whether minor wax components may additionally contribute to these tubules. Thin layer chromatography was used to prepare secondary alkanediol fractions from leaf cuticular waxes of Nelumbo nucifera and Thalictrum flavum, containing nonacosane-3,10-diol, nonacosane-4,10-diol, nonacosane-5,10-diol, nonacosane-7,10-diol, nonacosane-9,10-diol and nonacosane-10,13-diol. From organic solutions all these compounds crystallized in tubular shapes. Possible crystal structures of relevant alkanediol isomers are proposed, in analogy to the lattice geometries of comparable aliphatic compounds. The resulting structural model shows that nonacosan-10-ol and various secondary alkanediols may join in metastable mixed crystals. According to the structural model proposed the admixture of alkanediols to nonacosan-10-ol aggregates should enhance the stability of their tubular habit.     

Calcium and Salt Toleration by Bean Plants

The role of calcium in the salt relations of the bean plant, Phaseolus vulgaris, was examined. Brittle wax bush bean plants were cultured in nutrient solutions containing 50 mM NaCl. In the absence of added calcium the plants showed a general breakdown of the roots. A low concentration of calcium in the nutrient solution (0.1 mM) prevented this. Without added calcium the plants absorbed and translocated sodium at such a rate that high concentrations of it built up in the leaves within two days. With increasing concentrations of calcium in the nutrient solution the leaves contained progressively less sodium, and at 3 mM CaSO₄ the concentrations of sodium in the leaves was equal to that of the control plants grown without addition of salt. Even after both roots and stems had reached a high concentration of sodium, the leaves of plants grown in the presence of adequate concentrations of calcium contained little sodium.     

Performance of adult psyllids in no-choice experiments on juvenile and adult leaves of Eucalyptus globulus

The presence of glaucous juvenile leaves and glossy adult leaves in the canopy of the heteroblastic plant Eucalyptus globulus Labill., is a source of within-tree variation that affects herbivory by three psyllid species (Ctenarytaina eucalypti Maskell, C. spatulata Taylor and Glycaspis brimblecombei Moore) (Homoptera, Psyllidae). In no-choice field experiments with adult female psyllids in clip-on cages, we compared (1) leaf-settling, honeydew production, and survival of the Ctenarytaina species on juvenile and adult leaves of E. globulus, (2) leaf-settling and survival of G. brimblecombei on juvenile and adult leaves, (3) leaf-settling and survival of the three species on waxy (untreated) juvenile leaves and de-waxed (rubbed) juvenile leaves, and (4) leaf-settling and survival of C. spatulata on juvenile leaves from which wax was repeatedly removed. Leaf-settling by C. eucalypti was significantly greater on juvenile than adult leaves, however, honeydew production and survival were equal on both leaf types. In contrast, leaf-settling, honeydew production, and survival by C. spatulata were significantly greater on adult than juvenile leaves. Similarly, leaf-settling and survival by G. brimblecombei were significantly greater on adult than juvenile leaves. Wax removal from juvenile leaves significantly increased leaf-settling and survival of C. spatulata and G. brimblecombei. Although wax removal decreased leaf-settling by C. eucalypti, it did not affect survival. Repeated removal of regenerating wax from juvenile leaves did not affect leaf-settling or survival of C. spatulata. These results suggest that the epicuticular wax of juvenile leaves plays a role in resistance to C. spatulata and G. brimblecombei, however other unknown factors are probably also involved.