GLANDULAR CUTICLE FORMATION IN CANNABIS (CANNABACEAE)

Formation of the cuticle from components of the secretory cavity and subcuticular wall was studied by transmission electron microscopy of glandular trichomes of Cannabis prepared by high pressure cryofixation-cryosubstitution. Secretory vesicles in the secretory cavity resembled those localized in the subcuticular wall as well as the vesicle-related material associated with the irregular inner surface of the cuticle and appeared to provide precursors for thickening of the cuticle. Some contiguous vesicles in the secretory cavity and subcuticular wall lacked a surface feature at their point of contact, supporting an interpretation of vesicle fusion. Fibrillar matrix from the secretory cavity contributed fibrillar matrix to the subcuticular wall, and persisted as residual fibrillar matrix associated with secretory materials coalesced to the thickened inner surface of the cuticle. Elongated fibrils arranged in uniformly spaced parallel pairs contributed to the organization of fibrillar matrix in the subcuticular wall. Striae were evident in the outer portion of the cuticle, and appeared to represent sites of degraded residual fibrillar matrix associated with secretory materials coalesced to the inner cuticular surface. This study supports an interpretation that contents of secretory vesicles from the secretory cavity contribute to formation of glandular cuticle.     

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.     

CUTICLE DEVELOPMENT ON GLANDULAR TRICHOMES OF CANNABIS SATIVA (CANNABACEAE)

The dermal sheath of glandular trichomes of Cannabis sativa L., consisting of cuticle and a subcuticular wall, was examined by transmission electron microscopy. Cuticle thickened selectively on the outer wall of disc cells of each trichome prior to formation of the secretory cavity, whereas thickening was less evident on the dermal cells of the bract. Membraned secretory vesicles that differ in size and appearance in the secretory cavity were the source of precursors for synthesis of cuticle. Vesicle contents, released following the degradation of the vesicle membrane upon contact with the subcuticular wall, contributed to both structured and amorphous phases of cuticle development. The structured phase was represented by deposition and thickening of cuticle at the subcuticular wall-cuticle interface to form a thickened cuticle. In the amorphous phase precursors permeated the cuticle in a liquid state, as shown by fusion of cuticles and wax layers between contiguous glands, and may have contributed to growth in surface area of the expanding sheath. Disc cells are interpreted to control growth of secretory cavity by secretion of membraned vesicles into the cavity. The thickened cuticle, which increased eightfold in thickness during enlargement of the gland, provided structural strength for the extensive surface area of the dermal sheath. The gland of Cannabis in which vesicle contents contribute to the growth in thickness and surface area of the cuticle of the sheath is interpreted to represent a phylogenetically derived state as contrasted to secretory glands possessing only cuticle and lacking a complement of secretory vesicles.     

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.     

Cytochemical localization of cellulase in glandular trichomes ofcannabis (cannabaceae)

Cellulase reaction product was localized cytochemically at the ultrastructural level in the cell wall of disc cells, the secretory cavity and in the subcuticular wall of glands inCannabis. Cellulase reaction product was evident in the less dense region of the disc cell wall prior to secretory cavity formation. Reactivity in this region was associated with separation of an outer zone, forming the subcuticular wall, from the inner wall zone adjacent to the plasma membrane of the disc cells. Reaction product was associated with the disc cell wall and fibrillar matrix extending from it into the secretory cavity. Reactivity remained evident over the subcuticular wall throughout enlargement of the secretory cavity. Reaction product also was present over fibrillar matrix in the secretory cavity associated with both the inner wall and the subcuticular wall. The distribution of cellulase reaction product supports an interpretation that cellulase is involved in formation of the secretory cavity and subsequent redistribution of wall products to form the subcuticular wall during development of the secretory cavity.     

Secretory vesicle formation in the secretory cavity of glandular trichomes of Cannabis sativa L. (Cannabaceae)

The disc cell wall facing the secretory cavity in lipophilic glands of Cannabis was studied for origin and distribution of hyaline areas, secretory vesicles, fibrillar matrix and particulate material. Secretions evident as light areas in the disc cell cytoplasm pass through modified regions in the plasma membrane and appear as hyaline areas in the cell wall. Hyaline areas, surrounded with a filamentous outline, accumulate near the wall surface facing the secretory cavity where they fuse to form enlarged hyaline areas. Fibrillar matrix is related to and may originate from the dense outer layer of the plasma membrane. This matrix becomes distributed throughout the wall material and contributes in part to the composition of the surface feature of secretory vesicles. Thickening of the cell wall is associated with secretions from the disc cells that facilitates movement of hyaline areas, fibrillar matrix and other possible secretions through the wall to form secretory vesicles and intervesicular materials in the secretory cavity. The outer wall of disc cells in aggregate forms the basilar wall surface of the secretory cavity which facilitates the organization of secretory vesicles that fill the secretory cavity.     

Foliar secretory trichomes of Ocimum obovatum (Lamiaceae): micromorphological structure and histochemistry

This study characterises the micromorphology, ultrastructure and main chemical constituents of the foliar glandular trichomes of Ocimum obovatum using light and electron microscopy and a variety of histochemical tests. Two types of glandular trichomes occur on the leaves: large peltate and small capitate. The head of each peltate trichome is made up of four broad head cells in one layer. The head of each capitate trichome is composed of two broad head cells in one layer (type I) or a single oval head cell (type II, rare). In peltate heads, secretory materials are gradually transported to the subcuticular space via fracture in the four sutures at the connecting walls of the head cells. Release to the head periphery occurs through opposite fracture in the four sutures in the head cuticle. In type I capitate trichomes, release of the secretions to the subcuticular space occurs via a pore between the two head cells, and release to the head periphery occurs through the opposite pore in the head cuticle. In type II capitate trichomes, the secreted material is released from the head cell through a ruptured particular squared area at the central part of the head cuticle. These secretion modes are reported for the first time in the family Lamiaceae. Histochemical tests showed that the secretory materials in the glandular trichomes are mainly essential oils, lipophilic substances and polysaccharides. Large peltate trichomes contain a large quantity of these substances than the small capitate trichomes. Ultrastructural evidence suggests that the plastids produce numerous lipid droplets, and the numerous polysaccharide small vesicles are derived from Golgi bodies.     

Early Development of the Secretory Cavity of Peltate Glands in Humulus lupulus L. (Cannabaceae)

Early development of the secretory cavity of chemically fixed peltate glands in Humulus lupulus L. showed secretions with different densities, light, gray and dark, in the cytoplasm of disc cells and in the periplasmic space adjacent to the developing secretory cavity. Secretions were detected in the disc cell wall and subsequently in the developing secretory cavity under the subcuticular wall of the sheath. Light and gray secretions in the cavity possessed a membrane-like surface feature. Secretions were in contact with the irregular inner surface of the cuticle. Secretions contributed to the thickening of the cuticle, whereas the membrane-like surface feature contributed to a network of Cannabis striae distributed throughout the cuticle. This study supports an early development and organization of the secretory cavity in H. lupulus, parallel to those in Cannabis, and may represent common features for lipophilic glands in angiosperms.     

Capitate glandular trichomes of Helianthus annuus (Asteraceae): ultrastructure and cytological development

Previous studies have shown that capitate glandular trichomes (CGT) of the common sunflower, Helianthus annuus, produce sesquiterpene lactones (STL) and flavonoids, which are sequestered and accumulated between the apical cuticle and the wall of the tip cells. To explore the cellular structures required and putatively involved in the STL biosynthesis and secretion, the present study was focused on the development of CGT and the comparison of the ultrastructure of its different cell types. Gradual maturation of flowers in the capitulum of the sunflower provided the possibility to study the simultaneous differentiation from the primordial to the secretory stage of CGT located by light microscopy (bright field, differential interference contrast and fluorescence) as well as transmission electron microscopy. It was shown that the CGT of sunflower anthers had a biseriate structure with up to 14 cell pairs. In mature trichomes, the apical cells called secretory cells were covered entirely by a large cuticle globe, which enclosed the resinous terpenoids and was specialised in thickness and structure. The secretory cells lacked chloroplasts and contained mainly smooth endoplasmic reticulum (sER). Conspicuous cell wall protuberances and an accumulation of mitochondria nearby occurred in the horizontally oriented cell walls. The cytological differences between stalk cells and secretory cells indicate a different function. The dominance of sER suggests its involvement in STL biosynthesis and cell wall protuberances enlarge the surface of the plasmamembrane of secretory cells and may be involved in the secretion processes of STL into the subcuticular space.     

The fine structure of the tarsal glands of the honeybee Apis mellifera L. (Hymenoptera)

Summary Tarsal glands are located in the 6th tarsomere of adult honeybee queens, workers and drones. Their structural features are not cast or sex specific. The glandular epithelium is lined by a thin endocuticular layer. A cuticular pocket is formed from a postimaginal delamination of the cuticle secreted by the glandular epithelium. The apical plasma membrane of the glandular cells shows numerous cristae and microvilli lining large crypts that communicate with the subcuticular space. Pinocytotic vesicles, multivesicular bodies and residual dense bodies are present in the apical part of the glandular cells. The RER is well developed in perinuclear and basal parts of the glandular cells, but the Golgi apparatus is a discrete organelle without secretory granules. No exocytotic secretory structures were observed. To reach the glandular pocket, the non-proteinaceous secretory product must pass across the subcuticular space, the cuticular intima, the space between the intima and the cuticular wall, and the cuticular wall of the glandular pocket.     

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.     

Anatomical studies of the secretory structures: Glandular trichomes and ducts, in Grindelia pulchella Dunal (Astereae, Asteraceae)

The ultrastructure of the glandular trichomes and secretory ducts of Grindelia pulchella was studied. Plastids, mitochondria and endoplasmic reticulum are involved in the secretory process of both, trichomes and ducts. A special tissue with “transfer cells” is associated with the duct epithelial cells. The secretion is produced in the transfer cells and then is transferred to the duct epithelial cells where it accumulates in the vacuoles. The occurrence of cavities within the cell walls of the trichome cells and duct epithelial cells is described. The secretion is accumulated between the cell wall and the cuticle of these cells. When the cuticle is broken the secretion is released. We conclude that granulocrine secretion operates in this species.     

ULTRASTRUCTURAL DEVELOPMENT OF CAPITATE GLANDULAR HAIRS OF CANNABIS SATIVA L. (CANNABACEAE)

The capitate-sessile and capitate-stalked glands of the glandular secretory system in Cannabis, which are interpreted as lipophilic type glandular hairs, were studied from floral bracts of pistillate plants. These glands develop a flattened multicellular disc of secretory cells, which with the extruded secretory product forms the gland head and the auxiliary cells which support the gland head. The secretory product accumulates beneath a sheath derived from separation of the outer wall surface of the cellular disc. The ultrastructure of secretory cells in pre-secretory stages is characterized by a dense ground plasm, transitory lipid bodies and fibrillar material, and well developed endoplasmic reticulum. Dictyosomes and dictyosome-derived secretory vesicles are present, but never abundant. Secretory stages of gland development are characterized by abundant mitochondria and leucoplasts and by a large vacuolar system. Production of the secretory product is associated with plastids which increase in number and structural complexity. The plastids develop a paracrystalline body which nearly fills the mature plastid. Material interpreted as a secretion appears at the surface of plastids, migrates, and accumulates along the cell surface adjoining the secretory cavity. Extrusion of the material into the secretory cavity occurs directly through the plasma membrane-cell wall barrier.     

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.     

Structure and histochemistry of the extrafloral nectary ofAcacia terminalis (Salisb.) MacBride (Leguminosae,Mimosoideae)

Summary The extrafloral nectary ofAcacia terminalis is of the flat type and is located on the adaxial surface of the petiole of the bipinnate leaf. The secretory area is restricted to the base of the trough and no gaps or pores were detected by staining with vital dyes. Between the vascular bundles beneath the nectary and the surface cuticle there were three cell types. The cells of the flanking zone adjacent to the vascular bundles did not appear to be producing secretion whereas the cells of the glandular and secretory zones were secreting. The cells of the glandular zone were elongated whereas those of the surface secretory zone were spherical. Both had endoplasmic reticulum and Golgi bodies with secretory vesicles which were observed in close association with the plasmalemma. Secretion accumulated in the intercellular spaces of the glandular zone cells and forced the cells of the secretory zone apart. Symplastic contact was maintained in all cell types by plasmodesmata which were often associated with endoplasmic reticulum. Secretion accumulated beneath the cuticle which was distended but remained intact on the surface of the secretion.     

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     

Ultrastructure of posterior sternal glands of Macrotermes annandalei (Silvestri): new members of the sexual glandular set found in termites (Insecta)

In female alates of Macrotermes annandalei, two types of abdominal glands are involved in the secretion of sex pheromone. Tergal glands are found at the anterior margin of tergites 6-10 and posterior sternal glands (PSGs) are located at the anterior margin of sternites 6-7. The cytological features of both types of glands are quite similar. The fine structural organization of PSGs is studied more precisely and described for the first time. The glandular cuticle is pitted with narrow apertures corresponding to the openings of numerous subcuticular pouches. Several Class 3 glandular units open in each pouch. One canal cell and one secretory cell make an individual glandular unit. The canal cell is enlarged apically and is connected with the other canal cells to form a common pouch. Based on the structural features found in these glands, we propose a common secretory process for PSGs and tergal glands. During the physiological maturation of alates inside the nest, secretory vesicles amass in the cytoplasm of secretory cells, while large intercellular spaces collapse the cuticular pouches. At the time of dispersal flight, pouches are filled with the content of secretory vesicles while intercellular spaces are sharply reduced. After calling behavior, no secretion remains in the glands and pouches collapse again, while secretory cells are drastically reduced in size. The structure and the secretory processes of PSGs and tergal glands are compared to those of abdominal sexual glands known in termites.     

Glandular trichomes of Humulus lupulus var. Brewer's Gold: Ontogeny and histochemical characterization of the secretion

Leaves of Humulus lupulus possess two types of glandular trichomes: - peltate (lupulin) and bulbous.
Peltate trichomes are formed from a protodermal cell by two anticlinal divisions in perpendicular planes, followed by two periclinal ones that give rise to the initials of the head cells, the basal and the stalk cells. Head cells divide successively in radial and irregular planes. Fully developed peltate trichomes are built of a glandular head consisting of 30 to 72 cells, four stalk cells and four basal cells.
Bulbous trichomes are also formed from a protodermal cell by an anticlinal division followed by two periclinal ones that produce the initials of the glandular head cells, and the basal and stalk cells. Fully developed bulbous trichomes consist of four (occasionally eight) head glandular cells, two stalk cells and two basal cells.
The density of peltate trichomes decreases with the expansion of the leaves.
Both peltate and bulbous trichomes secrete essential oils. Peltate trichomes are the preferential site for the synthesis of bitter resins. Tannic acids could not be detected histochemically either in peltate or in bulbous trichomes. Both types of trichomes produce secretion that accumulates in the subcuticular space, being released, in the case of bulbous trichomes, by rupture of the cuticle.     

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