The Ultrastructure of Glandular Trichomes ofPhillyrea latifoliaL. (Oleaceae) Leaves

The anatomy and ultrastructure of glandular trichomes at differentdevelopmental stages were investigated inPhillyrea latifoliaL.leaves by transmission electron microscopy and histochemicaltechniques. The trichome consisted of a multicellular secretoryhead, a unicellular stalk and a collecting cell surrounded byepidermal cells and spongy mesophyll cells. There were numerousplasmodesmata across the cell walls of trichome cells, and especiallybetween the stalk cell and the collecting cell. The collectingcell and stalk cell contained few chloroplasts. Mitochondria,elements of the endoplasmic reticulum and small vacuoles wereabundant in the secretory cells. Crystals were present in thesecretory cells and the collecting cell, especially at the matureand senescent stages of trichome development. As the cuticle,which covered the secretory cells, did not show pores or perforations,it is proposed that secretion occurred by accumulation of productsin subcuticular spaces followed by diffusion through the cuticle.Callose accumulation was observed between the stalk cell andthe collecting cell of senescent trichomes, especially in salt-treatedplants. Trichome ontogeny was accelerated in salt-treated plants.Copyright1998 Annals of Botany Company Cuticle;Phillyrea latifolia; secretion; transmission electron microscopy; trichome development.     

Glandular Trichomes of Fagonia L. (Zygophyllaceae) Species: Structure, Development and Secreted Materials

The glandular trichomes ofFagoniaconsist of one secretory celland a multicellular stalk, which develops by division, elongationand elevation of epidermal cells. The latter become seperatedfrom the mesophyll and a subepidermal chamber is formed. Thelength of the stalk, which differs in the various species orvarieties is determined by the number of cell divisions and/or the extent of cell elongation. Although the basic morphologyand development of the trichomes of the species and varietiesexamined are similar, two types of mature trichomes can be distinguished:one occurs in the two examined varieties ofF. mollisand thesecond inF. glutinosaandF. arabica. The secretory cells of thesecond type possess a very thick wall and bear a porous cupuleon their top. Histochemical tests revealed that the sticky substancesecreted by the secretory cells contains mainly polysaccharidesand lipophilic compounds. The secreted material exhibits autofluorescence.InF. mollisvar.hispidachanges in the amount and shape of thefluorescent material inside the secretory cell, during the courseof development, have been observed. The contribution of theglandular trichomes inFagoniaspecies to survival in hot desertconditions is discussed. Fagonia; glandular trichomes; subepidermal chamber; secreted material; adaptation to desert conditions; stalk; fluorescence     

冬凌草腺毛的形态学及组织化学研究

利用光学显微镜对药用植物冬凌草地上部分腺毛的形态、分布和组织化学进行了研究。结果表明:(1)冬凌草的叶表皮有3种形态显著不同的毛,即非腺毛、盾状腺毛和头状腺毛;盾状腺毛和头状腺毛均具1个基细胞、1个柄细胞和头部;成熟的盾状腺毛的头部一般由4个分泌细胞组成,而头状腺毛头部由2个分泌细胞组成。(2)组织化学鉴定结果显示:2种腺毛中均含有黄酮类成分,盾状腺毛中还含有单萜、倍半萜等萜类成分;冬凌草甲素可能只存在于盾状腺毛中,但需要更直接的证据证明。研究认为,高密度的盾状腺毛可以作为筛选冬凌草高甲素含量品种的一项重要依据。     

The Ultrastructure of the Glandular Trichomes of Solanum tuberosum

The potato plant has two types of glandular trichomes whichwere investigated by electron microscopy. One type has a eight celled globular head on a neck cell anda stalk cell Each glandular cell has many rather large vacuoles,a large nucleus, many ribosomes and mitochondria, a few Golgibodies, and darkly coloured, often irregular plastids (chloroplasts).The plastids are mostly located near the axial cell wall borderinga large central intercellular space filled with secretion materialThe plastids are assumed to participate in the formation ofthe secretion material, which reacts positively to esterasetests. The outer wall is covered by a thin cuticle. The other type has a club-shaped multicellular head on a singlestalk cell. The cytoplasmic features in the cells are similarto those of the globular-headed trichome, except that they possesslarge central vacuoles and randomly distributed plastids. Centricendoplasmic reticulum has been observed in young cells. Intercellularspaces develop between the cells and into the outer wall, whichis thus split into two. Whereas the older glandular cells reactpositively to tests for esterase, the secretion material itselfis pectinaceous and reacts negatively. The outer wall is cutinizedand covered by a cuticle. Solanum tuberosum L., potato, glandular trichomes, ultrastructure     

Glandular Trichomes on the Leaves and Flowers of Plectranthus ornatus: Morphology, Distribution and Histochemistry

The types of glandular trichomes and their distribution on leavesand flowers of Plectranthus ornatus were investigated at differentstages of their development. Five morphological types of glandulartrichomes are described. Peltate trichomes, confined to theleaf abaxial surface, have, in vivo, an uncommon but characteristicorange to brownish colour. Capitate trichomes, uniformly distributedon both leaf surfaces, are divided into two types accordingto their structure and secretory processes. In long-stalkedcapitate trichomes, a heterogeneous secretion (a gumresin) isstored temporarily in a large subcuticular space, being releasedby cuticle rupture, whereas, in the short-stalked capitate trichomes,the secretion, mainly polysaccharidic, is probably exuded viamicropores. On the leaves, digitiform trichomes, which do notshow a clear distinction between the apical glandular cell andthe subsidiary cells, occur with a similar distribution to thecapitate trichomes. They do not develop a subcuticular space,and secrete small amounts of essential oils in association withpolysaccharides. The reproductive organs, particularly the calyxand corolla, exhibit, in addition to the reported trichomes,unusual conoidal trichomes with long unicellular conical heads.A large apical pore, formed by tip disruption, releases thesecretion (a gumresin) stored in a rostrum-like projection.On the stamens and carpels, digitiform, capitate and conoidaltrichomes are absent, but peltate trichomes are numerous. Theyoccur between the two anther lobes, on the basal portion ofthe style, and between the four lobes of the ovary. The resultspresented are compared with those of other studies on Lamiaceaeglandular trichomes. Copyright 1999 Annals of Botany Company Plectranthus ornatus Codd, Lamiaceae, glandular trichomes, morphology, histochemistry, essential oils and mucilage secretion.     

Foliar Nectaries and Glandular Trichomes in Catalpa (Bignoniaceae)

The Tertiary relic genus Catalpa, containing 11 Old and New World species, has multiple nectaries in the junctions of the major veins on the lower leaf surfaces. The generalized structure of the nectaries consists of a single, basal cell, and a single row of vertically oriented secretory cells. The nectaries are small, and contain no vascular tissue. Glandular and nonglandular trichomes are also present on the leaves. The glandular trichomes are structurally very similar to the nectaries, and probably are their precursors. Development of multiple nectaries in the lower leaf surface vein axils is considered to be an advanced strategy for attracting beneficial insects to control or minimize the effects of herbivorous insects. Chinese and American species of Catalpa are closely related, and have greater numbers of nectaries in more locations on the lower leaf surface than west Indian species. Herbivory pressures in the West Indies are postulated to be lower than on the continents, i.e. Asia and North America.     

Glandular Trichomes on Vegetative and Reproductive Organs of Leonotis leonurus (Lamiaceae)

The types of glandular trichomes, their ontogeny and patternof distribution on the vegetative and reproductive organs ofLeonotis leonurus at different stages of development, are studiedby light and scanning electron microscopy. Two morphologicallydistinct types of glandular trichomes (peltate and capitate)are described. Peltate trichomes, at the time of secretion,are characterized by a short stalk, which is connected witha large spherical head composed of eight cells in a single layer.Capitate trichomes can be divided into various types. Generally,they consist of a four-celled head supported by one or threestalk cells. The two kinds of trichomes differ in the secretionprocess. In the peltate trichomes, the secretory product seemsto remain accumulated in a subcuticular space, unless an externalfactor damages it. In the capitate trichomes, this product probablybecomes released through micropores. On the leaves peltate andcapitate trichomes are abundant, while on the flowers only thepeltate trichomes are numerous and the capitate are rare orabsent.Copyright 1995, 1999 Academic Press Leonotis leonurus R. Br., lion's ear, lion's tail, Lamiaceæ, glandular trichomes, morphology, ontogeny     

Ultrastructure of the Water-absorbing Trichomes of Pineapple (Ananas comosus, Bromeliaceae)

An ultrastructural study of dry and wet trichomes from the upperleaf surface of pineapple revealed that shield cells were normallydead and stalk cells were often living. In stalk cells of drytrichomes, polysaccharide material was present within vacuolesand a layered material was present between the plasma membraneand cell wall. In stalk cells of trichomes wet for 12 h vacuoleswere enlarged and appeared to contain little material. Layeredmaterial between the plasma membrane and cell wall was alsoabsent. In both wet and dry trichomes, numerous mitochondriawere present and plasmodesmata were observed connecting stalk,foot, and adjacent epidermal and mesophyll cells. It is suggestedthat the large numbers of mitochondria, which indicate highmetabolism, and the numerous plasmodesmata connecting the cells,provide indirect evidence for the function of the trichomesin uptake of dissolved nutrients. Ananas comosus (L.) Merr., pineapple, trichomes, ultrastructure, Bromeliaceae     

Development, Histochemistry and Ultrastructure of Gum-resin Ducts in Commiphora mukul Engl.

Gum-resin ducts are present in the primary and secondary phloemof Commiphora mukul Engl. The important gum-resin, known commerciallyas ‘guggul’, is secreted and collected in ductswhich develop schizogenously. The duct initials have dense cytoplasm,large nuclei, increased cytoplasmic RNA and proteins. The lumenof newly-formed ducts widens accompanied by anticlinal divisionsand subsequent tangential elongation of epithelial cells. Histochemicaltests reveal that the epithelial cells have apparently largeamounts of proteins, cytoplasmic RNA, and DNA in the nucleus.Lipid globules are also present in these cells. Epithelial cellwalls in contact with the duct are thin and of a loose fibrillarmesh. Microtubules, randomly oriented in the epithelial cellsare always parallel and adjacent to the wall. The cytoplasmis rich in ribosomes, endoplasmic reticulum, mitochondria, plastidsand vacuoles containing osmiophilic substances. At the peripheralregion of the duct, electron-transparent bodies containing densely-stainedmaterial are present close to the tangential wall.     

Accessory Pollen Adhesive from Glandular Trichomes on the Anthers of Leonurus sibiricus L. (Lamiaceae)

Abstract: Glandular trichomes (ca. 16 per anther) on the anthers of Leonurus sibiricus produce a secretion that, when touched, is liberated at once and becomes sticky when in contact with the air. With successive visitations of the pollinators (species of Bombus in naturalized populations) the number of secretion‐containing glands on each anther diminishes by mechanical rupture. On the pollinators, the secretion mixed with pollen was found adhered to the integument on the parts making contact with the anthers and stigma, mostly on the scape of the antennae. These trichomes are anatomically identical to the glandular scales common in the entire family and are formed by a multicellular cuticle‐bounded structure, with a foot and head. The secretion is accumulated as a milky emulsion under the cuticle, outside the primary cell wall, and is liberated by rupture of the cuticle. The composition possibly differs from what generally distinguishes these glandular trichomes, i.e. volatile oils that give these plants their particular smell. Such volatile compounds are generally assumed to have defensive or attractive functions, different from those observed in this study, which would be strictly mechanical.     

地黄叶和茎的解剖学及组织化学研究

采用解剖学和组织化学方法对地黄叶和茎的显微结构以及梓醇、多糖的分布进行观察研究,以明确梓醇和多糖在地黄叶和茎中的分布特征。结果显示:(1)地黄叶的上、下表皮均分布有腺毛和非腺毛,腺毛都属于头状腺毛,包括长柄和短柄的头状腺毛,两类腺毛的分泌物化学成分主要是黄酮和多糖;叶的上、下表皮上都分布有无规则型气孔,下表皮的气孔密度比上表皮的大,但气孔指数相差不大;栅栏组织由2～3层薄壁细胞构成,排列紧密,海绵组织薄壁细胞形状无规则,细胞间隙大。(2)组织化学研究表明,海绵组织中黄斑样的薄壁细胞是梓醇和多糖的贮存场所,这类薄壁细胞在叶片边缘的齿末端处最为集中,茎的皮层、韧皮部和木质部的薄壁细胞也都是梓醇和多糖的贮存场所。     

Development and Structure of Internal Glands and External Glandular Trichomes in Pogostemon cablin

Pogostemon cablin possesses two morphologically and ontogenetically different types of glandular trichomes, one type of bristle hair on the surfaces of leaves and stems and one type of internal gland inside the leaves and stems. The internal gland originates from elementary meristem and is associated with the biosynthesis of oils present inside the leaves and stems. However, there is little information on mechanism for the oil biosynthesis and secretion inside the leaves and stems. In this study, we identified three kinds of glandular trichome types and two kinds of internal gland in the Pogostemon cablin. The oil secretions from internal glands of stems and leaves contained lipids, flavones and terpenes. Our results indicated that endoplasmic reticulum and plastids and vacuoles are likely involved in the biosynthesis of oils in the internal glands and the synthesized oils are transported from endoplasmic reticulum to the cell wall via connecting endoplasmic reticulum membranes to the plasma membrane. And the comparative analysis of the development, distribution, histochemistry and ultrastructures of the internal and external glands in Pogostemon cablin leads us to propose that the internal gland may be a novel secretory structure which is different from external glands.     

龙葵腺毛发育的细胞学研究

利用光学显微镜、扫描电镜和透射电镜技术,观察了龙葵“四叶一心”期时叶片及茎表皮的腺毛的种类、分布,探究了不同类型腺毛的起源、生长、成熟、分泌、衰老等发育过程的细胞学特征;通过组织化学染色和荧光显微技术,观察了龙葵腺毛成分、分布,为龙葵的进一步开发利用提供参考。结果表明：（1）龙葵腺毛分为单细胞头腺毛和多细胞头腺毛两类,前者主要分布于茎表面和叶上下表皮,后者主要分布于茎表面的单细胞头腺毛之间、叶脉及叶边缘;（2）龙葵腺毛发育起始于表皮细胞突起,单细胞头腺毛行顶端生长,具1-4个柄细胞,四种类型;多细胞头腺毛可再分为一层、两层与三层多细胞头腺毛,另具三种特殊类型;（3）龙葵成熟腺毛具分泌能力,通过皮下空间的物质积累导致腺毛头细胞表面形成突起、包块、破口,最终释放分泌物;而头细胞与柄细胞随即皱缩、衰老。（4）超微结构显示,腺毛头细胞中内质网与高尔基体极为丰富,合成代谢及分泌活动活跃,产生大量包裹嗜锇物质的囊泡,囊泡与细胞壁融合,进而将嗜锇物质转移至细胞壁并积累,随后储存在角质层下的皮下空间直至分泌释放;（5）组织化学染色结果表明,腺毛含有萜类、生物碱、脂类、蛋白质、酚类和多糖。头细胞中主要含有萜类、生物碱、脂类、蛋白质、酚类和中性多糖;柄细胞中主要含有萜类、生物碱、脂类。     

Biochemical and Histochemical Localization of Monoterpene Biosynthesis in the Glandular Trichomes of Spearmint (Mentha spicata)

The primary monoterpene accumulated in the glandular trichomes of spearmint (Mentha spicata) is the ketone (−)-carvone which is formed by cyclization of the C₁₀ isoprenoid intermediate geranyl pyrophosphate to the olefin (−)-limonene, hydroxylation to (−)-trans-carveol and subsequent dehydrogenation. Selective extraction of the contents of the glandular trichomes indicated that essentially all of the cyclase and hydroxylase activities resided in these structures, whereas only about 30% of the carveol dehydrogenase was located here with the remainder located in the rest of the leaf. This distribution of carveol dehydrogenase activity was confirmed by histochemical methods. Electrophoretic analysis of the partially purified carveol dehydrogenase from extracts of both the glands and the leaves following gland removal indicated the presence of a unique carveol dehydrogenase species in the glandular trichomes, suggesting that the other dehydrogenase found throughout the leaf probably utilizes carveol only as an adventitious substrate. These results demonstrate that carvone biosynthesis takes place exclusively in the glandular trichomes in which this natural product accumulates.     

Characteristic Trichomes and Indumentum Specialization in African and European Parasitic Scrophulariaceae

Trichomes and their distribution patterns have been observed in the aerial parts of plants of the genera Striga, Buchnera, Rhamphicarpa, Euphrasia, Melampyrum and Rhinanthus, using both light (LM) and scanning electron microscopy (SEM). All trichomes belong to the multicellular, uniseriate category and can be classified as glandular and nonglandular types. On nearly all organs, the two types can be observed side by side. Apart from a large group of ubiquitous trichomes, some characteristic trichome types are reported; they are restricted either to chlorophyllous organs (foliage leaves, bracts, calyx and stem) or to the corolla. In some nonglandular trichomes mineral deposits have been found. Other morphological and anatomical trichome features are discussed with regard to their possible function.     

Cytochemistry and Ultrastructure of the Mucilage Secreting Trichomes of Nymphoides peltata (Menyanthaceae)

The young developing leaves in the buds of Nymphoides peltataare covered by a hyaline mucilage. The mucilage contains freesugars, polysaccharides and proteins. The most abundant monosaccharidesof the polysaccharide fraction are arabinose and galactose.Therefore, the major component of the mucilage is probably anarabinogalactan or arabinogalactan protein. The mucilage issecreted by glandular trichomes. It is suggested that both thepolysaccharide and the protein fraction of the mucilage aretransported to the plasmamembrane by vesicles of the Golgi apparatus(granulocrine secretion). Secretory proteins are probably synthesizedin the rough endoplasmic reticulum and transported to the Golgiapparatus via transition vesicles. Polysaccharides were localizedin Golgi vesicles by ultracytochemistry. After exocytosis thesecretion is accumulated between the cell wall and the cuticle;this leads to the formation of protrusions on the outer wallsof the glandular cells. Finally, the cuticle is ruptured andthe secretion is released. The biological function of the mucilageis not known. Possibly the mucilage is a lubricant or a protectionfrom desiccation. Nymphoides peltata (S.G. Gmel.) O. Ktz., trichomes, mucilage secretion, cytochemistry, ultrastructure     

Water Loss via the Glandular Trichomes of Chickpea (Cicer arietinum L.)

During late vegetative growth chickpea leaves and stems canbe covered with aqueous glandular droplets. If these dropletspersist at low humidities there may be substantial water lossvia the glandular trichomes Four solution culture experimentsin growth chambers tested for glandular water loss at differenthumidities. In the daytime, exudate persisted between relativehumidities of 55% and 95%, and the exudate water potential variedbetween - 2.0 M Pa and - 8.0 M Pa. Even by night, chickpea leaves,like wetted alfalfa leaves, were cooler than non-wetted alfalfaleaves or the ambient air. Daytime leaf temperatures were significantlyhigher in a mutant that produced fewer droplets than in itsnormal parent. It was concluded that water loss via the glandulartrichomes can be enough to lower leaf temperature by severaldegrees C within a wide range of atmospheric conditions. The exudate solutes, analysed to confirm the osmotic potentialmeasurements, were primarily malic, hydrochloric and oxalicacid. Without the strong acids a chickpea leaf, wet even ondry days, would be ripe for parasitic attack. Key words: Add exudate, leaf hairs, transpiration, leaf temperature     

Secondary Metabolites,Glandular Trichomes and Biological Activity of Sideritis montana L. subsp. montana from Central Italy

Sideritis montana subsp. montana is a small annual herb occurring in countries bordering the Mediterranean and Balkan regions. The secondary metabolism of this plant has not been fully explored so far. The aim of the present study was to understand the complex mixture of secondary metabolites and the type of secretory structures. The polar constituents were isolated by column chromatography from the ethanolic extract, and their structure was elucidated by NMR and MS. The essential oil was isolated by hydrodistillation and analysed by GC/MS. The plant indumentum was studied by light and scanning electron microscopy. To complete the work, the essential oil antioxidant activity and cytotoxicity on tumor cells were evaluated by DPPH, ABTS, FRAP, and MTT methods. Four different classes of secondary metabolites were isolated, namely flavonoids, caffeoylquinic derivatives, glycosidic hydroquinones and iridoids. The essential oil was mainly characterized by sesquiterpenene hydrocarbons. Peltate and long‐capitate hairs were the main sites where terpenes and polar constituents are produced. The secondary metabolites found in S. montana subsp. montana are of chemotaxonomic interest, some of them being typical of the genus Sideritis. The trichomes types observed partially differ from those described in other members of the genus Sideritis. The essential oil showed noteworthy inhibition on tumor cells.     

植物腺毛中防御物质的合成与调控及转运研究进展

植物毛状体来源于表皮细胞的延伸,是表皮细胞的特有结构。植物毛状体可分为腺毛和非腺毛,腺毛是具有分泌作用的毛状体,也是大量次生代谢产物的合成、储存以及释放的场所。植物腺毛常分泌不同类型的防御物质如萜类、氨基酸及苯丙烷类、酰基糖、脂肪类衍生物等,这些次生代谢物质能够保护植物免受生物和非生物胁迫,具有重要的防御作用。该文对近年来国内外有关植物腺毛的类型、防御物质的合成与调控等方面的研究进展进行综述,并重点对其合成途径、调控机理与转运机制的研究进展进行梳理,以期为防御物质的生物合成和遗传改良研究提供参考。     

Characterization of Secondary Metabolites,Biological Activity and Glandular Trichomes of Stachys tymphaea Hausskn. from the Monti Sibillini National Park (Central Apennines,Italy)

Stachys tymphaea (Lamiaceae) is a perennial herb growing in forest openings and dry meadows of central and southern Italy. It was investigated for the first time here, determining the content of secondary metabolites, the micromorphology of glandular trichomes, the histochemical localization of secretion, and the biological activity of the volatile oil, namely, the cytotoxic, antioxidant, and antimicrobial properties. The plant showed a peculiar molecular pattern, being rich of biophenolic compounds as flavonoids, phenylethanoid glycosides, and caffeoylquinic acid derivatives, but poor of iridoids, which are known as marker compounds of the genus Stachys. The essential oil was characterized by GC‐FID and GC/MS analyses, revealing a high percentage of sesquiterpene hydrocarbons (54.6%), with germacrene D (30.0%) and (E)‐β‐farnesene (12.4%) as the most abundant compounds, while other main components were representatives of the diterpenes (19.2%), represented mainly by (E)‐phytol (11.9%). This composition supported the taxonomic relationships in the genus Stachys, which comprises oil‐poor species producing essential oils rich in hydrocarbons, with germacrene D as one of the predominant components. The micromorphological study revealed three types of glandular hairs, i.e., Type A peltate trichomes, being the primary sites of essential oil biosynthesis, Type B short‐stalked trichomes, typical mucopolysaccharide producers, and Type C long capitate trichomes, secreting a complex mixture of both lipophilic and hydrophilic substances, with a major phenolic fraction. Moreover, the MTT assay revealed the potential of the volatile oil to inhibit A375, HCT116, and MDA‐MB 231 tumor cells lines (IC₅₀ values of 23.9–34.4 μg/ml).