The vacuolar-tubular continuum in living trichomes of chickpea (Cicer arietinum) provides a rapid means of solute delivery from base to tip

Summary A vacuolar continuum exists from base to tip in the secretory trichomes of chickpea (Cicer arietinum). This continuum is seen in living trichomes which have been labeled with Lucifer yellow CH and examined with confocal microscopy. It encompasses the large vacuole of the lower stalk cell, the vacuoles and tubules of the central stalk cell, the thin tubules of the upper stalk cell, and the tubules and vacuoles of the secretory head cells. The vacuolar-tubular system is structurally distinct within each cell, forming a gradient of large vacuoles in the lower stalk cell, thick tubules in the central stalk cell, and thin anastamozing tubules in the upper stalk cell. This membrane system appears to be continuous between trichome cells, as thin tubules emanate from plasmodesmata between stalk cells and between the upper stalk and lower head cell. In the upper stalk cell, the thin tubules of this continuum are streaming up and down the long axis of the cell at 0.67 m/s. The larger vacuolar-tubular system in the central and lower stalk cells is also slowly moving, with apparent peristalsis occurring in the central cell. The vacuolar-tubular system of the secretory head cells is completely labeled with Lucifer yellow when the dye has only partly diffused up the long walls of the trichome, indicating that the streaming tubular system delivers solute through the stalk cells to the secretory head cells faster than diffusion through the trichome walls. In the lower head cells, tubules emanate from the plasmodesmata connecting to the upper stalk cell, and these tubules are continuous with the head cell vacuoles. In addition, another layer of thin tubules forms along the edges of the secretory head cells, at the site of exocytotic secretion. We propose that the continuous vacuolar-tubular system in these trichomes functions to rapidly deliver solute from the base of the trichome to the secretory head cells. This system provides a pathway for the transport of secretory material.Dedicated to Prof. Dr. Dr. h.c. Eberhard Schnepf on the occasion of his retirement     

Developmental Ultrastructure of Glandular Trichomes of <Emphasis Type="Italic">Rosmarinus officinalis</Emphasis>: Secretory Cavity and Secretory Vesicle Formation

Glandular trichomes in the leaf lamina of Rosmarinus officinalis L. were examined by scanning and transmission electron microscopy. The leaves were characterized by an abundance of two types of glandular trichomes—small capitate and large peltate glandular trichomes. In addition to the glandular trichomes, numerous non-glandular trichomes were present on the abaxial surface of the leaf. These trichomes mainly predominated on the midrib, whereas glandular trichomes occurred on non-vein areas. At the initial phase of secretory cavity formation, hyaline areas were abundant in periclinal walls of head cells, while they were not observed in the anticlinal walls. The hyaline areas gradually increased in size, fusing with other areas throughout the wall. Loose wall material adjacent to hyaline areas was released from the head cell walls and migrated into the secretory cavities. As the secretory cavities continued to enlarge, the new vesicles emerging into the secretory cavities from the walls of head cells became surrounded with the surface of a typical membrane. They developed a round shape, but the contours of the vesicle surfaces appeared polygonal when tightly packed inside a cavity. These vesicles varied in size; small vesicles often possessed electron-dense contents, while large vesicles contained electron-light contents.     

Endocytosis in maize root cap cells

Summary Primary roots of maize seedlings have been treated with solutions of lanthanum and lead salts in an attempt to demonstrate endocytosis. Subsurface cells in the root cap reveal deposits of these heavy metals in coated pits in the plasma membrane and in coated vesicles. In addition lead deposits were observed in coated evaginations (pits) on large (secretory) vesicles present at the trans-pole of the Golgi apparatus and on small vacuoles. Lead was also found in the peripheral regions of individual cisternae throughout the dictyosomal stack. We interpret our results as providing evidence for coated pit/coated vesicle-mediated endocytosis and for the direct recycling of plasma membrane to the Golgi apparatus.     

Development and ultrastructure of glandular trichomes in<Emphasis Type="Italic">pelargonium x fragrans</Emphasis> ‘mabel grey’ (geraniaceae)

The glandular trichomes of leaves fromPelargonium xfragrans ‘Mabel Grey’ (Geraniaceae) were examined by light, scanning, and transmission electron microscopy. These trichomes had unicellular globular heads and stalks of different lengths and features. Two types were classified: Type I, with an elongated, large head and a short (100 μm), cylindrical stalk that was more apparent on the adaxial surface; and Type II, with a spherical, small head and a long (300μm), conical stalk that was more pronounced on the abaxial surface. The ultrastructure of secretory cells from both types was distinguished by a well-developed endoplasmic reticulum, mitochondria, plastids, dictyosomes, and numerous vacuoles that likely were involved in the storage and transport of lipophilic substances. Plasmodesmata were frequent on the walls of the secretory and stalked cells. Here, we discuss the implication of structural differentiation in these trichomes.     

Glandular trichomes of Ceratotheca triloba (Pedaliaceae): morphology, histochemistry and ultrastructure

This study was initiated to characterize the distribution, morphology, secretion mode, histochemistry and ultrastructure of the glandular trichomes of Ceratotheca triloba using light and electron microscopy. Its leaves bear two morphologically distinct glandular trichomes. The first type has long trichome with 8-12 basal cells of pedestal, 3-14 stalk cells, a neck cell and a head of four cells in one layer. The second type has short trichome comprising one or two basal epidermal cells, a unicellular or bicellular stalk and a multicellular head of two to eight cells. There is a marked circular area in the upper part of each head cell of the long trichome. This area is provided with micropores to exudate directly the secretory product onto the leaf surface by an eccrine pathway. The secretory product has copious amount of dark microbodies arising from plastids which are positive to Sudan tests and osmium tetroxide for unsaturated lipids. The secretion mode of short trichomes is granulocrine and involves two morphologically and histochemically distinct vesicle types: small Golgi-derived vesicles which are positive to Ruthenium Red test for mucilaginous polysaccharides; the second type is dark large microbodies similar to that of long trichomes with low quantity. These two types are stored in numerous peripheral vacuoles and discharge their contents accompanied by the formation of irregular invaginations of the plasmalemma inside the vacuoles via reverse pinocytosis. These two secretion modes of long and short trichomes are reported for the first time in the family Pedaliaceae. The long trichomes have more unsaturated lipids, while the short trichomes contain more mucilaginous polysaccharides.     

The essential oil secretory structures of Prostanthera ovalifolia (Lamiaceae)

The structure of the essential oil secretory tissues of Prostanthera ovalifolia R.Br was investigated using bright- and dark-field optical microscopy, and scanning and transmission electron microscopy. The leaves of P. ovalifolia have glandular trichomes of the peltate type common to many Lamiaceae species. The trichomes consist of a basal cell embedded in the epidermis, a stalk cell with heavily cutinized walls and a 16-celled secretory head, but they differ from those of many previously reported Lamiaceae species in their morphological form defined by the elevated cuticle. The sub-cuticular space contains a mixture of lipid and aqueous phases. Secretory cells have dense cytoplasm with many leucoplasts present. Volatile terpenoids are eliminated from the cytoplasm into the sub-cuticular space, the site of essential oil accumulation, via granulocrine secretion.     

THE HOST-PARASITE INTERFACE OF ALBUGO CANDIDA ON RAPHANUS SATIVUS

The fine structure of the intercellular hyphae of the obligate parasite Albugo candida infecting radish does not differ markedly from that described previously for cells of Peronospora manshurica. The stalked, capitate haustoria do not contain nuclei and are packed with mitochondria and lomasomes. The fungal plasma membrane and cell wall are continuous from the intercellular hypha throughout the haustorium except that there is no evidence of fungal cell wall around a portion of the haustorial stalk proximal to the haustorial head. Within the vacuolate host mesophyll cell, the haustorium is always surrounded by host plasma membrane and with at least a thin layer of host cytoplasm. The host cell wall invaginates at the point of haustorial penetration to form a short sheath around the region of penetration, but normally there is no host cell wall around the balance of the haustorium. About 1% of the haustoria observed were necrotic, and these were invariably walled-off completely from host cytoplasm by host cell wall. An amorphous, moderately electron-dense encapsulation lies between the haustorium proper and the host plasma membrane and extends into the penetration region between the sheath and the fungal cell wall. Invaded host cells contain more ribosomal-rich ground cytoplasm than uninfected cells. Glandular-like systems of tubules and connecting vesicles are often numerous in host cytoplasm in the vicinity of haustorial heads. These tubules open into the encapsulation, their limiting unit membranes being continuous with the host plasma membrane. We suggest that these represent a secretory mechanism of the host specifically induced by the parasite.     

ULTRASTRUCTURE AND DEVELOPMENT OF THE MICROSPORANGIUM OF PSEUDOTSUGA MENZIESII (MIRB.) FRANCO. I. DORMANT STAGES

The dormant (mid-November to mid-February) microsporangia of Pseudotsuga menziesii (Douglas-fir) contain pollen mother cells (PMC's) in diffuse diplotene, surrounded by 1–2 layers of tapetal cells and 3–4 layers of microsporangial wall cells. At the beginning of dormancy, PMC's are large and their walls are lysed. The cell walls contain a thick layer of loosely-arranged fibrils which are produced in large vesicles in the PMC cytoplasm and are secreted across the plasma membrane. PMC's contain several layers of rough ER. The inner tangential and the radial walls of the tapetal cells are lysed. During dormancy the PMC's form many new autophagic vacuoles, the chromatin consists of a network of fine threads comprised of medium-sized granules of uniform size and the nucleoli split. The outer tapetal wall is thick and becomes encrusted by an irregular lipid layer. The tapetal cytoplasm is similar to the PMC cytoplasm but is devoid of amyloplasts. The tapetal cytoplasm shows secretory activity at the beginning of dormancy and again near the end of dormancy. The later secretory activity results in the deposition of a spongy material, especially along the radial and inner walls of the tapetal cells. Tapetal cells contain 1–2 large nuclei which show prominent and irregular clumps of chromatin. Subcellular developmental changes occur in the dormant microsporangia of Pseudotsuga in much the same manner as has been reported for Pinus.     

The distribution of lead in duckweed (Lemna minor L.) root tip

While considerable information on lead distribution in the cells of terrestrial plants has been collected, little is known about lead localization in the cells of the aquatic plant. Lemna minor L. (duckweed) roots were examined using X-ray microanalysis. After 1-h treatment with lead, its concentration was the highest in small vacuoles. After 6 and 12 h, the lead content of cell walls gradually increased. The changes of lead level between vacuoles and cell walls may result from redistribution of this metal from symplast to cell walls or it may reflect increased apoplastic transport. Lead was not found in the ground cytoplasm of any variants of the experiments. This fact and presence of lead in small vesicles suggests that endocytosis may play the role in lead uptake in Lemna.     

Glandular scale development and essential oil secretion in Origanum dictamnus L.

Glandular scales of Origanum dictamnus L. originate from a single protodermal cell. They are composed of a 12-celled head and an unicellular stalk and foot. During the early stages of gland differentiation, the head cells possess a small number of plastids which contain globular inclusions. Similar inclusions are also observed in the plastids of the stalk and the foot cell. The lateral walls of the stalk cell progressively undergo cutinization which does not extend to the upper and lower periclinal walls. At the onset of secretion the electron density of the plasmalemma region lining the apical walls of the head cells remarkably increases. These walls are impregnated with an osmiophilic substance identical in appearance to the content of the subcuticular space. In a following stage of the secretory process osmiophilic droplets of various size arise in the cytoplasm of the secretory cells which undergoes simultaneously a reduction of its initial density. After secretion has been concluded the protoplast of the head cells becomes gradually degenerated. The chlorenchyma cells of the mesophyll possess numerous microbodies closely associated with various organelles. In the cytoplasm of these cells crystalloids occasionally occur.     

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.     

线纹香茶菜叶上腺毛发育的细胞学研究

为进行中药溪黄草基原植物的品种鉴定,采用光镜和电镜对线纹香茶菜(原变种)[Isodon lophanthoides var.lophanthoides]叶上腺毛的发育进行细胞学研究。结果表明,线纹香茶菜具有头状腺毛和盾状腺毛2种类型。头状腺毛无色透明,由1个基细胞、1个柄细胞和1或2个头部分泌细胞构成;盾状腺毛为红色,由1或2个基细胞、1个柄细胞和4~8个分泌细胞构成头部。2种腺毛均由原表皮细胞经两次平周分裂形成,后因柄细胞和头部细胞所处的分化状态不同而形成两类腺毛。2种腺毛超微结构表明,质体、高尔基体和粗面内质网为主要分泌物产生和运输的细胞器。当盾状腺毛成熟时,角质层下间隙充满了分泌物,其分泌物的性质很可能决定了线纹香茶菜腺毛的颜色。     

ULTRASTRUCTURE OF GLANDULAR TRICHOMES OF LEAVES OF NICOTIANA TABACUM L., cv XANTHI

Electron microscopy confirms previous light microscope observations that tobacco leaf trichomes are glandular and that there are two different types. Both the tall trichome (multicellular stalk, unicellular or multicellular head) and the short trichome (unicellular stalk; multicellular head) exhibit characteristics common to gland cells—a dense cytoplasm, numerous mitochondria, and little vacuolation. The tall trichome contains structurally well developed chloroplasts and an elaborate network of endoplasmic reticulum. The short trichome contains undifferentiated plastids and endoplasmic reticulum which parallels the nucleus and plasmalemma. Few dictyosomes are seen either in the short trichome or in the tall trichome. The short trichome appears to undergo structural changes concurrently with the appearance of secretory product within the cells. The most noticeable change is the formation of the extraplasmic space between the cell wall and the plasmalemma. Electron dense secretory product is observed between the plasmalemma and the cell wall and within the intercellular spaces.     

甘草腺毛的形态发生和组织化学研究

利用扫描电镜及薄切片技术对甘草的腺毛形态发生和发育过程进行了观察,并对腺毛发育过程中黄酮类成分积累进行了组织化学定位研究。结果表明：甘草腺毛为多细胞构成的盾状腺毛,有长柄和短柄2种类型;前者主要分布在花萼片上,而后者主要分布于叶片上。组化鉴定结果显示：腺毛中存在着黄酮类成分、其他亲脂类和非纤维素多糖类成分;在腺毛的发育过程中,黄酮类物质是随腺毛的发育成熟,在头部盘状结构的分泌细胞及角质层下腔中积累。研究结果对进一步探讨甘草叶中黄酮类成分的合成及其作用提供科学依据。     

DEVELOPMENT,STRUCTURE AND FUNCTION OF SECRETORY TRICHOMES IN PSYCHOTRIA BACTERIOPHILA (RUBIACEAE)

Mucilage-secreting dendroid trichomes develop from the adaxial epidermis of young stipules surrounding the shoot apex. Each trichome consists of a multicellular stalk from which radiate many branch cells. The trichome has no cuticle and the branch cell walls distally are loose cellulosic frameworks. Dictyosomes produce vesicles whose products are secreted through the plasma-lemma and cell wall. Enlarged portions of the ER are frequently associated with dictyosomes and may be part of the system for synthesis and transport of secretion products. Bacteria, which later occur in leaf nodules, are present in the mucilage surrounding trichomes and young leaves. The latter develop stomata through which the bacteria enter. As stipules and leaves grow out of the apical region, the secretory trichomes degenerate and are replaced by non-secretory ones.     

SECRETORY CAVITY DEVELOPMENT IN GLANDULAR TRICHOMES OF CANNABIS SATIVA L. (CANNABACEAE)

Development of the secretory cavity and formation of the subcuticular wall of glandular trichomes in Cannabis sativa L. was examined by transmission electron microscopy. The secretory cavity originated at the wall-cuticle interface in the peripheral wall of the discoid secretory cells. During the presecretory phase in development of the glandular trichome, the peripheral wall of the disc cells became laminated into a dense inner zone adjacent to the plasma membrane and a less dense outer zone subjacent to the cuticle. Loosening of wall matrix in the outer zone initiated a secretory cavity among fibrous wall materials. Membrane-bound hyaline areas, compressed in shape, arose in the wall matrix. They appeared first in the outer and subsequently in the inner zone of the wall. The membrane of the vesicles, and associated dense particles attached to the membrane, arose from the wall matrix. Hyaline areas, often with a conspicuous electron-dense content, were released into the secretory cavity where they formed rounded secretory vesicles. Fibrous wall material released from the surface of the disc cells became distributed throughout the secretory cavity among the numerous secretory vesicles. This wall material was incorporated into the developing subcuticular wall that increased five-fold in thickness during enlargement of the secretory cavity. The presence of a subcuticular wall in the cavity of Cannabis trichomes, as contrasted to the absence of this wall in described trichomes of other plants, supports a polyphyletic interpretation of the evolution of the secretory cavity in glandular trichomes among angiosperms.     

SECRETORY VESICLE FORMATION IN GLANDULAR TRICHOMES OF CANNABIS SATIVA (CANNABACEAE)

Formation of secretory vesicles in the noncellular secretory cavity of glandular trichomes of Cannabis saliva L. was examined by transmission electron microscopy. Two patterns of vesicle formation occurred during gland morphogenesis. 1) During initial phases of cavity formation small hyaline areas arose in the wall near the plasma membrane of the disc cell. Hyaline areas of elongated shape and different sizes were distributed throughout the wall and adjacent to the secretory cavity. Hyaline areas increased in size, some possibly fusing with others. These hyaline areas, possessing a membrane, moved into the cavity where they formed vesicles. As membraned vesicles they developed a more or less round shape and their contents became electron-dense. 2) During development of the secretory cavity and when abundant secretions were present in the disc cells, these secretions passed through the wall to accumulate as membraned vesicles of different sizes in the cavity. As secretions emerged from the wall, a membrane of wall origin delimited the secretory material from cavity contents. Vesicles released from the wall migrated in the secretory cavity and contacted the sheath where their contents permeated into the subcuticular wall as large or diffused quantities of secretions. In the subcuticular wall these secretions migrated to the wall–cuticle interface where they contributed to structural thickening of the cuticle. This study demonstrates that the secretory process in glands of Cannabis involves not only secretion of materials from the disc cell, but that the disc cell somehow packages these secretions into membraned vesicles outside the cell wall prior to deposition into the secretory cavity for subsequent structural development of the sheath.     

Ontogeny resolves gland classification in two caesalpinoid legumes

Robust glandular appendages are reported in legumes of the Caesalpinieae tribe. Most studies only attempt to describe the external morphology of these structures, without providing a distinction between glandular trichomes and emergences. This study employed ontogeny to resolve the terminology of these structures present in flowers of two tropical woody legumes of Caesalpinieae, Erythrostemon gilliesii and Poincianella pluviosa, through surface, anatomical and ultrastructural analyses. Flowers of both species exhibit branched and non-branched glandular trichomes since these structures originate from a single protodermal cell. Non-branched glandular trichomes occur on the inflorescence axis, pedicel, sepals and ovary; in P. pluviosa, they also occur in the unguicle of wings and standard, filaments, anthers and style. This type of trichome shows a non-secretory multiseriate stalk and a secretory multicellular head. Branched glandular trichomes, with similar morphology but exhibiting non-secretory branches, occur in the inflorescence axis, pedicel and sepals; in P. pluviosa, they also occur in the unguicle of wings. During the secretory phase, the trichome head cells have large nuclei, cytoplasm rich in vacuoles, oleoplasts, mitochondria, rough endoplasmic reticulum and free ribosomes. The content is released in the intercellular spaces of the head in a merocrinous mechanism and reaches the surface through cuticle rupture. We emphasized the importance of ontogenetic studies to clarify the terminology of secretory structures. This type of study should be performed in other caesalpinoids so that such robust glandular appendages can be correctly interpreted and used with phylogenetic value in the group.     

ULTRASTRUCTURE OF GLANDULAR OVARIAN TRICHOMES OF CYPRIPEDIUM CALCEOLUS AND C. REGINAE (ORCHIDACEAE)

Trichomes on the orchid ovary are a possible site of synthesis and secretion of the floral scent. Scanning electron microscopy of these trichomes shows a bulbous cell on a two-celled stalk. Thin sections of the tip cell revealed the morphology of an active, secretory cell with unusual coated vesicles in the extra-cellular deposition. Abundant smooth endoplasmic reticulum (ER) aggregated beneath the plasma membrane in the apical region of the cell and the limited dictyosomes in the cell suggest direct secretion by ER. Numerous lipid droplets are present in the apical area. Plastids, found only in the basal region of this cell, are more round in profile than typical chloroplasts and contain only a few unstacked thylakoids and a limited membranous reticulum. In addition to the normal plastid envelope, a double layer of membrane (probably ER) is tightly appressed to each dense, starch-free plastid. Highly specialized morphology and subcellular localization of organelles suggest the secretory nature of these trichomes.     

Structural investigation of the glandular trichomes of <Emphasis Type="Italic">Salvia argentea</Emphasis>

The morphology, anatomy and distribution of glandular trichomes on the aerial organs of Salvia argentea L. has been investigated. Two morphologically distinct types of glandular trichomes were determined. Capitate glandular trichomes forming a base 1–7 celled, a stalk 1–5 celled or no stalk and a head uni- or bicellular had various types. In capitate trichomes, the neck cell that has an important role especially for xeroformic plants, acting to prevent the backflow of secreted substance through the apoplast has been distinctively observed in the investigated species. The capitate trichomes were present abundantly on all aerial organs of S. argentea. Peltate glandular trichomes had a large secretory head forming 1–5, 8 central and 8–10, 12, 14 peripheral cells. Peltate trichomes are present on all aerial organs, except petiole, being the most abundant on calyx and corolla. Results were shown by tables and photographs.