Structure and distribution of floral trichomes in Lycaste and Sudamerlycaste (Orchidaceae: Maxillariinae s.l.)

Phylogenetic analysis indicates that Lycastinae should be incorporated into a more broadly defined Maxillariinae. This is supported by several anatomical features, including the presence of sunken, glandular trichomes in both Lycastinae and Maxillariinae s.s. Until recently, these were known only from vegetative organs, but have since been reported from flowers of Maxillaria dichroma. One character currently used to distinguish between Lycaste and Sudamerlycaste is the distribution of floral trichomes. In this article, we test the reliability of this character, describe the floral micromorphology of Lycaste and Sudamerlycaste and investigate whether their flowers bear sunken hairs. Their floral micromorphology is compared with that of other genera currently assigned to Maxillariinae s.l. Flowers of Lycaste and Sudamerlycaste bear conical or obpyriform papillae and unbranched and unequally branched multicellular trichomes. Contrary to previous reports that trichomes are confined to the column in Sudamerlycaste, they also occur in the tepal axils. Labellar trichomes, although often present in Lycaste, are lacking in Sudamerlycaste. In Lycaste sections Lycaste and Aromaticae, floral trichomes tend to be unbranched, whereas section Intermediae has both unbranched and branched hairs. Branched hairs are more common in Sudamerlycaste. Some hairs are tracheoidal, pitted and lignified. These mainly occur in section Lycaste and, to a degree, in section Intermediae, but are absent from section Aromaticae and most species of Sudamerlycaste. Branched column hairs, present in Sudamerlycaste, are absent from all sections of Lycaste, and tracheoidal column hairs occur only in Sudamerlycaste. Sunken floral hairs are absent from both genera. Trichome structure and distribution may prove useful in distinguishing between these taxa and in elucidating the intergeneric relationships of Maxillariinae s.l.© 2010 The Linnean Society of London, Botanical Journal of the Linnean Society, 2010, 164 , 409–421.     

Leaf anatomy ofDombeya andNesogordonia (Sterculiaceae), emphasizing epidermal and internal idioblasts

We studied leaf anatomy, using clearings, resin sections, and scanning electron microscopy, from mostly herbarium specimens of 123 species ofDombeya and 11 species ofNesogordonia (Sterculiaceae). Species were placed in seven idioblast categories, ranging from those without any to single and bicelled epidermal forms to multicelled nodules and single mesophyll idioblasts. Idioblast contents are possibly mucilaginous, but were not identified. In these two genera the range of foliar idioblast morphology surpasses that known previously for the entire family. Leaves are dorsiventral with mostly abaxial anomocytic stomata and typical palisade and spongy layers; paraveinal mesophyll is lacking. Miniature glandular (clavates, capitates) and nonglandular (mostly stellate) trichomes occur. Prismatic crystals predominate; epidermal prismatics and mesophyll druses are rare.     

Evolution of trichome types and its systematic significance in the genus Phlomoides (Lamioideae–Lamiaceae)

Despite a number of recent molecular phylogenetic studies on Phlomoides, in terms of trichome morphology the genus is still among the most poorly studied taxa in the family Lamiaceae. In order to test the utility of trichome characters for delimitation of sections, subsection and species of Phlomoides, we examined trichomes of 64 species representing all recognized sections and subsections using stereomicroscopy and scaning electron microscopy. Two basic types of trichomes could be identified: non‐glandular and glandular. Both trichome types can be simple or branched. The glandular trichomes were sessile, short stalked or long stalked. Different kinds of branched trichomes were observed in most species of P. sect. Phlomoides, i.e. symmetrically stellate, stellate with a central long branch, bi‐ or trifurcate. The species of P. sect. Filipendula were mostly covered by simple trichomes. Moreover, variation in trichome characters appears to have particular value, not only for the classification at sectional or subsectional rank, but also for delimitation of species within each section. For example, all studied species of P. subsect. Fulgentes are characterized by various kinds of stellate trichomes, while the trichome variability in P. subsect. Tetragonae was sufficiently high for species discrimination. An ancestral character state reconstruction was performed in order to investigate the evolution of trichome types and it revealed the following evolutionary trends in trichome characters of Phlomoides: 1) branched trichomes are primitive in Phlomoides as compared to simple ones, 2) long simple non‐glandular trichomes are derived as compared to short simple ones and 3) the presence of stalked glandular trichomes is advanced as compared to subsessile or sessile ones.     

Trichome micromorphology of Iranian Stachys (Lamiaceae) with emphasis on its systematic implication

Trichomes of 37 taxa of the genus Stachys and one species of Sideritis (S. montana) were examined using light and scanning electron microscopy. The indumentum shows considerable variability among different species, but is constant among different populations of one species, and therefore, affords valuable characters in delimitation of sections and species. The characters of taxonomic interest were presence of glandular and non-glandular trichomes, thickness of the cell walls, number of cells (unicellular or multi-cellular), presence of branched (dendroid) trichomes, presence of vermiform trichomes, orientation of trichomes in relation to the epidermal surface, curviness of trichomes, and presence of papillae on trichome surface. Two basic types of trichomes can be distinguished: glandular and non-glandular trichomes. The glandular trichomes can in turn be subdivided into subtypes: stalked, subsessile, or sessile. The stalks of the glandular trichomes can be uni- or multi-cellular. Simple unbranched and branched trichomes constitute two subtypes of non-glandular trichomes. Our data do not provide any support for separation of Sideritis from Stachys. The following evolutionary trends are suggested here for Stachys: vermiform trichomes with stellate base are primitive against vermiform trichomes with tuberculate base, long vermiform trichomes are primitive against the short simple trichomes, appressed trichomes are advanced against spreading ones, and loss of glandular trichomes is advanced against their presence. Overall, trichome micromorphology is more useful in separation of species within sections rather than characterizing large natural groups known as sections, except for few cases.     

Glandular trichomes and essential oil constituents ofCalamintha menthifolia (Lamiaceae)

Plant material ofCalamintha menthifolia was collected from two populations grown in the Vikos-Aoos area (NW. Greece). The structure and ontogeny of the glandular trichomes and the chemical composition of the secreted essential oil were studied. The leaves ofC. menthifolia have numerous glandular trichomes of three morphological distinct types: 1) glandular scales with a unicellular foot and stalk, and a 12-celled head, 2) glandular hairs with a unicellular foot and stalk, and a unicellular pear-shaped head and 3) glandular hairs with a unicellular foot, a bicellular stalk and a unicellular elongated head. Qualitative and quantitative GC-MS analyses of the essential oils revealed piperitone oxide as the main constituent in both populations. In the light of these results the relationships beweenC. menthifolia and other members of theSatureja group as well as its taxonomy are discussed.     

Beiträge zur Systematischen Anatomie derAsteraceae-Anthemideae: Die Trichome

Biseriate glandular trichomes and uniseriate flagellar covering hairs occur in all or most of the 20 genera examined and thus do not provide important taxonomical hints. In contrast, T- or Y-shaped hairs have been found inSantolina, Anthemis, Leucanthemopsis, Dendranthema, Tanacetum,Balsamita, Sphaeromeria (?),Artemisia, andAchillea clavenae only. Stellate hairs appear to be rare (inSantolina andArtemisia sect.Dracunculus). For details, additional hair types, and relationships see Tab.1 and Fig. 6.     

Hair morphology and systematics ofPhysalis (Solanaceae)

Hair morphology was exammed on developing seedlings and mature plants of ten species from five of seven series inPhysalis. The taxonomic importance of hair development and the distribution of hair types then was evaluated with respect to other comparative data. Two classes of hair types were observed, as found in earlier investigations ofSolanum andRhododendron. The first hair class comprises a sequence from unbranched hairs to dendroid-stelliform hairs. Hairs of this class show considerable variability among taxa in size, presence or absence of glandular tips, and presence and degree of branching, and so were useful in making taxonomic comparisons. The second hair class consists of short hairs, each tipped with a multicellular gland. This second hair class was not useful taxonomically because of its lack of variability in morphology and its often rare occurrence on a plant. The taxa studied exhibit distinctive trichome features which serve to distinguish series and, in some cases together with other data, provided new insight into previously enigmatic species relationships.     

Trichoderma species form endophytic associations within Theobroma cacao trichomes

Trichoderma species are usually considered soil organisms that colonize plant roots, sometimes forming a symbiotic relationship. Recent studies demonstrate that Trichoderma species are also capable of colonizing the above ground tissues of Theobroma cacao (cacao) in what has been characterized as an endophytic relationship. Trichoderma species can be re-isolated from surface sterilized cacao stem tissue, including the bark and xylem, the apical meristem, and to a lesser degree from leaves. SEM analysis of cacao stems colonized by strains of four Trichoderma species (Trichoderma ovalisporum-DIS 70a, Trichoderma hamatum-DIS 219b, Trichoderma koningiopsis-DIS 172ai, or Trichoderma harzianum-DIS 219f) showed a preference for surface colonization of glandular trichomes versus non-glandular trichomes. The Trichoderma strains colonized the glandular trichome tips and formed swellings resembling appresoria. Hyphae were observed emerging from the glandular trichomes on surface sterilized stems from cacao seedlings that had been inoculated with each of the four Trichoderma strains. Fungal hyphae were observed under the microscope emerging from the trichomes as soon as 6 h after their isolation from surface sterilized cacao seedling stems. Hyphae were also observed, in some cases, emerging from stalk cells opposite the trichome head. Repeated single trichome/hyphae isolations verified that the emerging hyphae were the Trichoderma strains with which the cacao seedlings had been inoculated. Strains of four Trichoderma species were able to enter glandular trichomes during the colonization of cacao stems where they survived surface sterilization and could be re-isolated. The penetration of cacao trichomes may provide the entry point for Trichoderma species into the cacao stem allowing systemic colonization of this tissue.     

The defensive role of trichomes in black medick (Medicago lupulina,Fabaceae)

Simple and gland-tipped trichomes occur in varying proportions in the cosmopolitan weed black medick (Medicago lupulina L.). Densities of both simple and glandtipped trichomes were separately negatively correlated with the amount of damage to leaves in herbarium collections from throughout the world. This indicates that both types of trichomes are protective against herbivores, but suggests that the two types of hair differ in effectiveness against different species. Since an average of less than 1% herbivore consumption of the foliage of black medick was observed, it is remarkable that adaptive value of the trichomes was demonstrable. In a greenhouse experiment, both gland-tipped and simple hairs provided considerable resistance against whitefly oviposition. For both herbarium collections and the greenhouse experiment, conspicuously fewer gland-tipped hairs than simple hairs were required to achieve a given level of resistance to insects. Low trichome density considerably reduced damage in comparison to the absence of trichomes, while increasing density was progressively less efficient, suggesting that moderate pubescence is the most desirable strategy.     

新疆14种青兰属植物叶表皮微形态结构研究

应用光学显微镜和扫描电镜,对新疆14种青兰属(DracocephalumL.)植物叶片的微形态特征进行观察,结果表明:该属植物只有宽齿青兰(Dracocephalum paulsenii Briq.)叶的下表皮细胞为多边形,其余种植物叶的上、下表皮均为不规则形;垂周壁式样有深波状、波状、浅波状、平直-弓形;气孔器均为横列型;气孔形状有椭圆形、长椭圆形、宽椭圆形、近圆形;表皮毛的类型为小刺毛、短柔毛、长柔毛、头状腺毛和盾状腺毛。在不同种间甚至是同种植物叶的上、下表皮上,气孔器的大小、气孔密度、气孔指数、气孔外拱盖内缘、表皮毛、角质层纹饰等的微形态特征都存在很大的差异,可为探讨本属种间的分类、亲缘关系和演化趋势提供理论依据。     

Morphology and distribution of trichomes in Italian species ofTeucrium sect.Chamaedrys (Labiatae) — a taxonomical evaluation

Micromorphology and distribution of trichomes (both secretory and not) in different parts of plants of the five Italian species belonging toTeucrium sect.Chamaedrys have been studied. These characters neatly evidence the differences between the taxa considered; of particular interest are the observations concerning the dense coverage of peltate hairs on the abaxial face of the leaves ofT. flavum subsp.glaucum and the characters contributing to a better identification ofT. marum andT. subspinosum. The importance of the calyx indumentum as distinctive taxonomical character of the genusTeucrium is confirmed, stressing at the same time the necessity of completing the observations at micromorphological level.     

The foliar micromorphology of Solanum pseudocapsicum

Foliar micromorphology of Solanum pseudocapsicum was investigated by electron microscopical examination. The leaves are characterized by anisocytic stomata which are more abundant on the abaxial surfaces. The leaves have short multicellular glandular trichomes sparsely distributed over the entire leaf surfaces. Crystal deposits were also observed on the surfaces above the stomata. Energy dispersive X-ray spectroscopy-SEM showed that Al, K, Na and Si were the major constituents of the crystals analyzed. The presence of glandular trichomes in this plant could be the source of poisonous compounds that are characteristic of this species.     

Accumulation and turnover of 2-tridecanone in Tetranychus urticae and its consequences for resistance of wild and cultivated tomatoes

In this study we assessed the dynamic changes of 2-tridecanone in a herbivorous mite (Tetranychus urticae) on tomato (Lycopersicon esculentum, cv. Moneymaker), a plant with methyl ketones in the tetracellular tips of the glandular trichomes (Type VI). We showed that spider mites accumulate 2-tridecanone when foraging on cultivated tomato. Thus, the rate of mite–trichome contact multiplied by the amount of toxin per trichome tip exceeded the relative rate of toxin turnover multiplied by the amount of toxin per mite. The relative rate of toxin turnover was estimated to be 1.1 per day on cucumber, a plant without this toxin. The amount per trichome tip varied from 0.33 ng for middle-leaf trichomes to 1.26 ng for main-stem trichomes. Hence, to achieve a static level of 2-tridecanone equal to 8–17 ng per mite – representing the level we found in mites on middle leaves – the rate of mite–trichome contact should be 26–57 per day. Because methyl ketone apparently accumulates in the spider mites on tomato, the rate of mite–trichome contact is probably higher than that. We expect the accumulation of ketones to occur especially on the stems of cultivated tomato, since this is the area most densely occupied with glandular hairs and because here the hairs have higher levels of the methyl ketones.Using dose–response relationships assessed earlier (Chatzivasileiadis and Sabelis, 1997, 1998), we estimated that the number of mite–trichome contacts causing 50% mortality per day is equal to 88 on a tomato stem, whereas it equals 70 for another strain of spider mites collected from cucumber. On wild tomato, L. hirsutum f. glabratum (PI 134417), just one to two contacts would suffice to cause 50% mortality per day. We suggest that methyl ketones from glandular hairs on tomato are an important mortality factor for spider mites on wild tomato and probably also on cultivated tomato.     

Micromorphological and phytochemical characters ofTeucrium marum andT. subspinosum (Labiatae) from Sardinia and Balearic Islands

Micromorphology and distribution of trichomes in different plant parts ofTeucrium marum andTeucrium subspinosum from Sardinia and the Balearic Islands are described. The composition of volatile compounds in the same plants has also been studied. The occurrence in Sardinia of two differentT. marum entities is evidenced. One of them, growing in the NW. part of the island, is very similar toT. marum from Minorca.T. subspinosum from Sardinia and Majorca differ for the presence in the last one of short capitate hairs and for a higher ratio of dolichodial/teucrein. While the degree of variability of all the characters is very high, there is a good homogeneity between all the taxa, due to the presence of monoterpene cyclopentanoids not found until now in other species.     

新疆委陵菜属不同花柱组植物叶表皮微形态结构的研究

利用光学显微镜和扫描电子显微镜,观察了新疆委陵菜属5组不同花柱组10种4变种植物叶表皮的微形态特征,测量统计叶表皮毛的类型、表皮细胞的形状及大小、气孔器的分布及类型、气孔的形状、大小、密度及指数、气孔外拱盖形态及其纹饰等指标。结果显示:新疆委陵菜属10种4变种植物叶的下表皮均有气孔器的分布,形状为长椭圆形、椭圆形、宽椭圆形和近圆形;气孔器的类型多为无规则四细胞型、无规则型、围绕型和辐射型;表皮毛的类型为针状毛、带状柔毛和腺毛;表皮细胞的形状分为不规则形和多边形2种类型。研究表明,新疆委陵菜属植物表皮毛特征、叶片表皮细胞的形状、垂周壁式样、气孔器的形状类型、气孔密度指数及外围蜡质纹饰等存在差异,对属以下等级的划分有重要价值,可作为物种分类及鉴别的依据,同时也为本属一些分类群间的系统关系的探讨提供佐证。     

Glandular Trichomes on Alfalfa Impede Searching Behavior of the Potato Leafhopper Parasitoid

New cultivars of alfalfa, Medicago sativa L., have been released with glandular trichomes for resistance to potato leafhopper, Empoasca fabae (Harris). Yet, the impact of the glandular trichomes on the primary natural enemy of the leafhopper, Anagrus nigriventris Girault, is unknown. We compared the host searching behavior of the egg parasitoid on four alfalfa clones varying in trichome characters. Female wasps were videotaped on Ranger, a susceptible clone with relatively sparse trichomes, B14, a resistant clone with dense but nonglandular trichomes, and FG12 and FG18, two resistant clones with glandular trichomes. Although the number of leafhopper eggs per stem exposed to wasps did not significantly differ among the four clones, the frequency of foraging and total foraging time were less on the two clones with glandular trichomes than on the two clones with nonglandular trichomes. In addition, an analysis of covariance demonstrated that, although the number of ovipositional probes increased with egg density on a stem, the number of probes on stems with glandular trichomes was significantly less than that on stems without glandular trichomes. The allocation of time by wasps among drumming, probing, and grooming behaviors was similar among the clones. Wasps tended to fly off of clones with glandular trichomes more often than off of clones with nonglandular trichomes. This study suggests that cultivars with glandular trichomes may interfere with host searching by A. nigriventris.     

Glandular trichomes of Solanum berthaultii and its hybrids with potato deter oviposition and impair growth of potato tuber moth

Glandular trichomes on foliage of the wild potato species, Solanum berthaultii Hawkes, deter oviposition by the potato tuber moth (PTM), Phthorimaea operculella Zeller and negatively affect other important performance parameters. Oviposition deterring factors are localized in the glandular trichomes of S. berthaultii. When mechanically transferred to foliage of a susceptible potato cultivar, trichome contents reduced egg laying by 97%. Removal of glandular trichomes from S. berthaultii foliage using a combination of chemical and mechanical procedures increased oviposition rates ca. 210-fold. Removal of trichomes also led to increased mobility of larvae on the leaf surface, more leaf feeding, shorter larval development and larger pupae. The resistance conferred by glandular trichomes of S. berthaultii provides an important genetic trait potentially useful for management of PTM.     

The trichomes of pericarp in Juglans (Juglandaceae): scanning microscopy, fluorescent microscopy amd histochemistry

Four types of glandular and non-glandular trichomes of pericarp in four Juglans species (J. ailanthifolia, J. cordiformis, J. mandshurica and J. regia) from Juglandaceae were studied by scanning electron microscopy, fluorescent light microscopy and histochemistry. The capitate trichomes on short stalk, the capitate trichomes on long stalk and the peltate trichomes belong to glandular trichomes; the simple hairs concern to non-glandular trichomes. The investigated species differ one from another in dimensions and distribution oftrichomes as well as the chemical content and the mechanism of secretion. The fluorescent markers and histochemical tests show the presence of flavonoids, tannins and polyphenols in trichomes on short and long stalk. In peltate trichomes the flavonoids and tannins were found in lesser quantity and the polyphenols are absent. In simple hairs the phenolic substances have not been recognized. It has been come out with the suggestion about a functional role of each type of trichomes.     

Micromorphological and chemical characterisation of Stachys recta L. subsp. serpentini (Fiori) Arrigoni in comparison to Stachys recta L. subsp. recta (Lamiaceae)

Stachys recta L. is a very polymorphous species in which numerous subspecies were recognised. S. recta L. subsp. serpentini (Fiori) Arrigoni is a typical endemism growing on serpentine soils in northern Apennines and particularly in Tuscany (Italy). In order to contribute to a better knowledge of this plant and to its differentiation with respect to S. recta L. subsp. recta, the micromorphological characters (non-glandular and glandular trichomes) and the essential oil composition of the two subspecies were investigated. Micromorphological characters were studied using scanning and transmission electron microscopy, while light microscopy was used for histochemical observations. Essential oil analysis was carried out by gas chromatography and mass spectrometry.In the two examined taxa, the morphology and distribution of glandular and non-glandular trichomes, and the different essential oil composition, may be considered distinctive characters at subspecies level. This is consistent with the taxonomic classification considering S. recta subsp. serpentini a subordinate taxon of S. recta.     

Inhibition of Telenomus sphingis an egg parasitoid of Manduca spp. by trichome/2-tridecanone-based host plant resistance in tomato

The resistance of accession PI 134417 of the wild tomato Lycopersicon hirsutum f. glabratum C. H. Mull to Manduca sexta (L.) (Lepidoptera: Spingidae) and Leptinotarsa decemlineata (Say) (Coleoptera: Chrysomelidae) is conditioned by the high densities of 2-tridecanone-containing, glandular trichomes associated with the foliage. In laboratory experiments, rates of parasitism of M. sexta eggs by Telenomus sphingis (Ashmead) (Hymenoptera: Scelionidae) were lower among eggs on PI 134417 foliage than among eggs on foliage of the cultivated tomato L. esculentum Mill. (cv. Better Boy). The latter is characterized by a significantly lower density of type VI glandular trichomes than PI 134417 and an absence of 2-tridecanone. Parasitism by T. sphingis was also reduced among eggs on foliage of the F₁ hybrid between PI 134417 and L. esculentum. The hybrid foliage lacks 2-tridecanone but has a density of type VI glandular trichomes that is intermediate between those of PI 134417 and L. esculentum, indicating that elevated densities of type VI glandular trichomes adversely affect T. sphingis. This conclusion was further substantiated by the finding that there were no differences among plant lines in the levels of parasitism of M. sexta eggs when the eggs were on foliage that had been divested of glandular trichomes.In bioassays in which T. sphingis adults or immatures in host eggs were exposed to filter paper treated with 2-tridecanone at rates comparable to those associated with PI 134417 foliage, 2-tridecanone was acutely toxic and caused high levels of mortality. In addition, at high concentrations, 2-tridecanone vapors were repellent to T. sphingis adults. However, when exposed to PI 134417 foliage, few T. sphingis adults were killed.Parasitism of M. sexta eggs was unaffected when the eggs were deposited by moths reared as fifth instar larvae on diet containing 2-tridecanone and/or 2-undecanone at levels comparable to those associated with PI 134417 foliage.