The Development, Structure and Function of Dendroid Colleters in Psychotria kirkii Hiern (Rubiaceae)

The dendroid colleters of the leaf nodulated Rubiaceous shrubPsychotria kirkii Hiern. have been studied with respect to theirdevelopment, structure and function. The colleters, which arisefrom the adaxial surface of stipules of apical and lateral shoots,secrete a protein/carbohydrate mucilaginous substance in whichis maintained a colony of leaf nodule bacteria. The colletersare multicellular and multiseriate, consisting of a two to fourcell thick stalk from which radiate up to 70 elongate secretorybranch cells. Cuticle envelops both stalk and branch cells inearly developmental stages and as secretory activity increasesthis cuticle is largely lost in two different ways. The majorpart is forced off the branch cell surface through the passageof a largely carbohydrate component of the mucilage which surroundsthe colleters: a second method of cuticle loss involves thepassage from the cell of small electron-translucent bodies whichbecome coated with cuticle as they exit the cell. The mucilagein which the bacterial cells are found provides a vehicle wherebythe bacteria are able to enter the leaves, thus leading to theinitiation of leaf nodules. Psychotria kirkii Hiern., secretory dendroid colleters, symbiosis, ultrastructure, trichome development     

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     

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.     

The Structure and Cytochemistry of the Pistil of Sternbergia lutea (Amaryllidaceae)

Studies were carried out on structural and cytochemical aspectsof the pistil of Sternbergia lutea (L.) KerGawl. The stigmais of the wet papillate type; the papillae are unicellular andare arranged densely around the rim of a funnel-shaped stigma.The stigma exudate is limited and is confined to the bases ofthe papillae and the inner lining of the stigma. The papillaeare smooth in the distal part and are covered with intact cuticle-pelliclelining. The cuticle is disrupted at places towards the baseof the papillae releasing the exudate. The exudate is rich inpectins and other polysaccharides but poor in proteins and lipids.The papillae show dense cytoplasmic profiles with extensiveendoplasmic reticulum (ER), abundant mitochondria, polyribosomesand active dictyosomes. The style is hollow. The stylar cavityis surrounded by two to four layers of glandular cells. In theyoung pistil the canal is lined with a continuous cuticle, butin the mature pistil the cuticle becomes disrupted and the canalis filled with the secretion produced by the cells of the surroundingglandular tissue. Ultrastructurally, the cells of the glandulartissue are very similar to the stigmatic papillae. The innertangential wall of the cells bordering the canal is uniformlythicker than other walls. The secretion in the stylar canal,as well as the intercellular spaces of the glandular tissue,stain intensely for pectins and polysaccharides but poorly forproteins and lipids. Pollen tubes grow through the stylar canal.Structural and cytochemical details of the pistil of Sternbergiaare compared with other hollow-styled systems. Pistil, Sternbergia lutea (L.) Ker-Gawl., stigma and style, structure and cytochemistry     

Histochemistry and Senescence of Colleters of Allamanda cathartica (Apocynaceae)

Allamanda have colleters on the adaxial bases of petiole, bractsand bracteoles. Each colleter is finger shaped, differentiatedinto a long head on a short stalk. Vasculature to the colleteris absent but branched laticifers are present among the centralcells. Secretion of the colleter contains glucose and rhamnose.The major elements present in the exudate are Na, Fe and Zn.Starch, protein and lipids were identified, with lipids themajor component. Petiolar colleters are persistent and becomestiff due to the lignification occurring in the walls of epithelialand central cells. Because of over-lignification in the centralcells, the cell lumen is highly reduced. Allamanda, colleter, laticifer, secretion, senescence     

The Cuticle, Epidermis and Stomatal Ontogeny of Casuarina equisetifolia Forst

The cuticle, epidermis and stomatal ontogeny of Casuarina equisetifoliaForst. is described. The cuticle shows well marked impressionsof the epidermal cells and stomata. The epidermis of leaf andstem shows transversely oriented, tetracytic, mesoperigenousstomata with two lateral mesogene subsidiaries and two polarperigene neighbouring cells. Although the epidermal structureof Casuarina shows a good deal of resemblance with that of theBennettitales, it may not indicate any phylogenetic relationshipssince there are important differences in the structure and reproductionof the plants of these two groups.     

Ontogenesis secretion and senescence of Tocoyena bullata (Vell.) Mart. (Rubiacaeae) colleters

Colleters are secretory structure present on many families including Rubiaceae. Particular characteristics have been described about colleters secretory cells, however senescence process are still under debate. Tocoyena bullata (Vell.) Mart. (Rubiaceae) shoot apex were collected at Jardim Botânico do Rio de Janeiro, RJ/Brazil. Stipules were separated and fragments were fixed in 2.5% glutaraldehyde and 4.0% formaldehyde in 0.05 m sodium cacodylate buffer, pH 7.2, post fixed in 1.0% osmium tetroxide in the same buffer, dehydrated in acetone, critical‐point‐drying, sputtered coated and observed. For light microscopy fragments were fixed and dehydrated, infiltrated with historesin and stained with 1% toluidine blue. For transmission electron microscopy, the samples were infiltrated with Epoxi resin. Colleters are present on stipule adaxial surface. On the beginning of development, these structures are recognized as small projections. Later on, colleters differentiated and secrete by cuticle rupture. The colleters senescence occurs in a concomitant and indissoluble way of programmed cell death. Ultrastructural analyses during the process strongly suggest the senescence is based on a non‐autolitic programmed cell death. T. bullata colleters, present at stipule abaxial surface are cylindrical secretory structures. Colleters secretory cells originated as stipule projections; differentiate; secrete and senesce by programmed cell death. The secretion and the cell dead occurs in a concomitantly and indissoluble way.     

A Biochemical and Cytochemical Study of the Cuticle-associated Peroxidases in Lupinus

A biochemical and cytochemical study of peroxidases (EC 1.11.1.7 [EC] )associated with the outermost cell layers of Lupinus albus hypocotylshas been performed. Cytochemical investigations showed thatin the epidermis of lupin hypocotyls, peroxidatic activitiescould be detected mainly at the level of the endoplasmic reticulum,Golgi apparatus, ground substance of the cytoplasm, intercellularspaces between adjacent epidermal cells, and in the cuticlelayer. No peroxidatic reactions were seen at the level of eitherthe radial or the tangential walls. The cuticle peroxidaticreaction was due to two acidic isoperoxidases, also found incell walls of vascular tissues, and was further characterizedthrough a study of its catalytic activities. These studies showedthat cuticle-associated peroxidases were able to oxidize genistein,but unable to oxidize ascorbic acid. These results suggest thatextracellular peroxidases associated with the outermost celllayers of lupin hypocotyls are involved more in the metabolismof isoflavones of the cuticle layer than in the growth responsesof the whole organ. Epidermal cell, cuticle, peroxidase cytochemistry, genistein oxidation, Lupinus albus     

Cytochemical and Morphological Evidence for the Involvement of the Plasma Membrane and Plastids in Mucilage Secretion in Aloe arborescens

Most of the volume of Aloe arborescens leaves (volumetric density= 0.68±0.08) is occupied by a mucilage tissue. The mucilagesof Aloe species are glucomannans of great medical and pharmaceuticalimportance. An electron microscopical and histochemical studywas carried out, following the development of the tissue andsecretion processes. In contrast to other reports on polysaccharide secretion inplants, no observable activity was found in the Golgi apparatus.In the young stages of leaf development, positive histochemicalstaining for polysaccharides and structural changes were foundmainly in the plastids. In the mature leaves the mucilage cellsremain alive and intact and secretory activity appears to becentered in the plasma membrane. Aloe arborescens, cytochemistry, mucilage, plasma membrane, plastids, secretion     

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     

The Involvement of Glucose-6-Phosphatase in Mucilage Secretion by Root Cap Cells of Zea mays

In order to determine the involvement of glucose-6-phosphatasein mucilage secretion by root cap cells, we have cytochemicallylocalized the enzyme in columella and peripheral cells of rootcaps of Zea mays. Glucose-6-phosphatase is associated with theplasmalemma and cell wall of columella cells. As columella cellsdifferentiate into peripheral cells and begin to produce andsecrete mucilage, glucose-6-phosphatase staining intensifiesand becomes associated with the mucilage and, to a lesser extent,the cell wall. Cells being sloughed from the cap are characterizedby glucose-6-phosphatase staining being associated with thevacuole and plasmalemma. These changes in enzyme localizationduring cellular differentiation in root caps suggest that glucose-6-phosphataseis involved in the production and/or secretion of mucilage byperipheral cells of Z. mays. Zea mays, corn, glucose-6-phosphatase, columella cell, peripheral cell, mucilage, secretion, cytochemistry     

The Structure and Cytochemistry of the Stigma-style Complex ofCorylus avellanaL. 'Tonda Gentile delle Langhe' (Corylaceae)

Structural and cytochemical aspects of the stigma-style complexofCorylus avellanawere studied. In cross section the stigmaticstyle consists of papillae, one or two layers of sub-epidermalcells and a central transmitting tissue. The papillae coverthe style for about 80% of its length, are unicellular and arecoated with a cuticle-pellicle. During development, the cellwalls of the papillae increase in thickness and between them,below the cuticle, lipid bodies are observed. The sub-epidermalcells are similar in cell content to the papillae. The centraltransmitting tissue consists of highly vacuolated cells andthe intercellular spaces are filled with a proteic and polysaccharidicsubstance. Both the transverse and longitudinal walls containplasmodesmata.Copyright 1998 Annals of Botany Company cytochemistry, stigma and style, ultrastructure,Corylus avellana     

Ultrastructure and Radiolabelling of Leaf Cuticles from Ivy (Hedera helixL.) Plantsin vitroand duringex vitroAcclimatization

Cuticle ultrastructure and radiolabelling of isolated cuticlesafter incorporation of [¹⁴C] acetate in foliar discs were investigatedwith ivy plants grownin vitrothenex vitro. Results show an increasein thickness, mass and wax content, between young and expandedleaves, for bothin vitroandex vitrocuticles. The cuticle ofinvitrounexpanded leaves was very thin and only constituted alamellate zone. The ultrastructure ofin vitroyoung and expandedleaf cuticles showed characteristics similar toin situcuticles.The thickness of the lamellate zone remained fairly constantand represented 33% of the cuticle thickness in young leaves,but only 11.4% in expanded leaves. The number of lamellar unitsdecreased from 14 to nine between these two growth stages. Themain difference between young leaves developedin vitroorex vitrowasa thinner lamellate zone forex vitrocuticles. However, theselatter cuticles had an intermediary zone between the lamellateand reticulate zones. The cuticle thickness of expanded leaveswas greater forin vitrocuticles suggesting a temporary decreasein cuticle biosynthesis after transfer of the plant fromin vitrotoexvitro.Results from cuticle radiolabelling show higher radioactivityincorporation in cuticles isolated from leaves developedex vitrocomparedtoin vitro. This radiolabelling was particularly marked forexvitroyoung leaf cuticles and depended on the duration of theexvitrogrowth period revealing a progressive activation of cuticlebiosynthesis in response to new environmental conditions. Hedera helix; ivy leaf cuticle; in vitroplants; electron microscopy; radiolabelling; isolated cuticles     

Colleters in Bathysa cuspidata (Rubiaceae): Development,ultrastructure and chemical composition of the secretion

This paper describes the development of colleters of Bathysa cuspidata, Rubiaceae, considering anatomical, histochemical and ultrastructural aspects and going from first differentiation stages until senescence. Further, the chemical composition of the secretion is investigated. The samples were prepared according to the usual techniques for light microscopy and scanning and transmission electron microscopy. Electrophoresis and thin layer chromatography (TLC) were used to confirm the results obtained in the histochemical tests. The colleters occur at the ventral surface of the stipules which protect the leaf primordia as well as the shoot meristem. The origin of the colleters is mixed, involving protoderm and ground meristem. The Bathysa colleters are of the standard type or are bifurcated; this latter type is documented here for the first time for Rubiaceae. Colleter secretion is a mucilage rich in protein, as determined by histochemical tests and confirmed by chemical analysis. Phenolic compounds and terpenes were detected only in the colleters themselves, but not in the secretion. The epithelial cells present conspicuous nuclei and nucleoli and the cytoplasm is rich in dictyosomes, endoplasmic reticulum, mitochondria, vesicles and small vacuoles with a fibrillar content. The accumulation of phenolic compounds and terpenes, the formation of a large central vacuole, the increase of the intercellular and subcuticular spaces occupied by the secretion and, finally, the darkening and the wilting of the colleters characterize the senescence of these structures. The secretion process of the colleters of B. cuspidata suggests a process of programmed cell death.     

Neurosecretion and Molting in Some Parasitic Nematodes

The adult female of Ascaris lumbricoides possesses a numberof nerve cells containing material which stains with paraldehyde-fuchsin.Among others, most of the primary sensory cells in the lipsare fuchsinophilic. Ascaris does not survive outside its host,so that it is impossible to ascribe a function to these cells. Phocanema decipiens possesses similar cells in the dorsal andventral ganglia which exhibit a cycle of secretion correlatedwith the burst of cytological activity which accompanies thedeposition of the new cuticle. Ligation experiments have demonstratedthat a new cuticle can be deposited in the absence of theseneurosecretory cells. Our most recent experiments suggest thatthe neurosecretory cells may control the release of leucineaminopeptidase in the excretory gland, a substance which isthought to be responsible for ecdysis.     

Leaf colleters in Tontelea micrantha (Celastraceae,Salacioideae): Ecological,morphological and structural aspects

The colleter secretion can be useful to protect plants of Cerrado (Brazilian savanna) biome during the long and pronounced dry season. This study describes the presence of colleters in Tontelea micrantha and represents the first record of these structures in Celastraceae. To investigate colleter structure and their secretory processes, young leaves were collected, fixed, and processed according to conventional techniques for light, and electron microscopy. Colleters were observed at the marginal teeth on the leaf. They produce mucilaginous secretions that spread over the leaf surface. After secretory phase, colleters abscise. The secretory epithelium is uniseriate and composed of elongated cells whose dense cytoplasm is rich in organelles. The ultrastructure of the secretory cells is compatible with the pectin-rich secretion. Observations of the young leaves surface revealed the presence of superficial hydrophilic secretion films that appeared to have the function of maintaining the water status of those organs.     

Labellar anatomy and secretion in Bulbophyllum Thouars (Orchidaceae: Bulbophyllinae) sect. Racemosae Benth. & Hook. f.

Background and Aims

Floral secretions are common in Bulbophyllum Thouars, and the labella of a number of Asian species are said to produce secretions rich in lipids that act as food rewards for insect pollinators. Although some of these reports are based on simple histochemical tests, a much greater number are anecdotal and, hitherto, neither the ultrastructure of the labellum nor the secretory process has been investigated in detail. Furthermore, sophisticated histochemical approaches have generally not been applied. Here, both the labellar structure and the secretory process are investigated for four species of Asian Bulbophyllum sect. Racemosae Benth. & Hook. f., namely Bulbophyllum careyanum (Hook.) Spreng., B. morphologorum Kraenzl., B. orientale Seidenf. and B. wangkaense Seidenf., and compared with those of unequivocal lipid-secreting orchids.

Methods

Labellar, secretory tissue was investigated using light microscopy, scanning electron microscopy, transmission electron microscopy and histochemistry.

Key Results

The adaxial median longitudinal groove of the labellum contained secretory tissue comprising palisade-like epidermal cells, similar to those of certain lipid-secreting Oncidiinae Benth. However, these cells and their secretions gave positive results mainly for protein and mucilage, and their organelle complement was consistent with that of cells involved in protein and mucilage synthesis. Sub-cuticular accumulation of secretion resulted in cuticular distension and blistering. The sub-epidermal layer of isodiametric parenchyma contained starch and, like the epidermal cells, ultrastructure consistent with mucilage synthesis. Lipids were mainly confined to the cuticle, and hardly any intracellular lipid droplets were observed.

Conclusions

It is proposed that mucilage is produced by dictyosomes present in the palisade-like epidermal cells. Mucilage precursors may also be produced by these same organelles in sub-epidermal cells and are thought to pass along the symplast via plasmodesmata into the adjoining palisade-like secretory cells, which contain abundant arrays of rough endoplasmic reticulum. Here, they become chemically modified and form a protein-rich, mucilaginous secretion that, following vesicle-mediated transport across the cytoplasm, traverses the cell wall and accumulates in blisters formed from the distended cuticle. Rupture of these blisters releases the secretion onto the labellar surface. However, in certain species, there is some evidence that the secretion may traverse the cuticle via cuticular pores, and micro-channels may permit the passage of fragrance. Hydrolysis of sub-epidermal starch probably generates the carbohydrate and, together with mitochondria, much of the energy required for the secretory process. This anatomical organization resembles that found in certain lipid-secreting, Neotropical species of Bulbophyllum and Oncidiinae, but since the chemical composition of their secretions is different, and these taxa occur on a separate continent and have different insect pollinators, parallelism of floral anatomy is likely.     

Elaiophore diversity in three contrasting members of Oncidiinae (Orchidaceae)

The elaiophores of Trichocentrum cavendishianum (Bateman) M.W. Chase & N.H. Williams, Oncidium loefgrenii Cogn., and Gomesa recurva R. Br. display considerable morphological and anatomical diversity. Oil secretion by flowers of T. cavendishianum and O. loefgrenii can be related to the presence of saddle-like, labellar elaiophores and the labellar callus, respectively, whereas, in G. recurva , although oil is present, no obvious structure appears to be involved in its secretion. In the first two species, the secretory tissue consists of palisade-like cells, whereas, in G. recurva , these cells are oval. Many Oncidiinae are thought to mimic members of the Malpighiaceae, and the elaiophores of that family also contain palisade-like cells that may indicate evolutionary convergence. As oils accumulate below the elaiophore cuticle, that of T. cavendishianum becomes distended, whereas that of the other two species does not. Full discharge of oil from the elaiophores of T. cavendishianum probably occurs only after the cuticle is ruptured by a visiting insect, and this may contribute towards pollinator selection.  © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 155 , 135–148.     

Epidermal Structure and Ontogeny of Stomata in Vegetative and Reproductive Organs of Ephedra and Gnetum

The epidermal structure and development of stomata in vegetativeand reproductive organs of Ephedra foliata and Gnetum ula isdescribed. The epidermal cells are polygonal, isodiametric,or elongated with thick or thin straight, arched, or slightlysinuous anticlinal walls. The cuticle is thin or thick. Papilla-likeunicellular outgrowths are present in Ephedra foliata. The maturestomata are orientated parallel to the longitudinal axes orirregularly. The mature stomata are anomocytic, paracytic, witha single subsidiary cell, cyclocytic, and actinocytic. Arresteddevelopment, contiguous stomata, and stomata with aborted guardcells have been observed. The ontogeny of stomata on differentorgans of these two plants is typically haplocheilic or perigenousbut the stomatal apparatus varies from organ to organ.     

Pollen-Stigma Interaction in the Leguminosae: the Organization of the Stigma in Trifolium pratense L.

The intact stigma of Trifolium pratense possesses a smooth receptivesurface fringed by a few ranks of brush hairs. This surfaceis ensheathed by a thin (75–100 nm) but highly impermeablecuticle, which encloses four to five ranks of secretory cellsimmersed in their secretory products. Experimental single-grainpollinations show that pollen cannot become hydrated or germinateon the intact surface. The cuticle is ruptured when the floweris tripped; the secretion is released, and captured pollen-selfor cross-can then germinate. As in other papilionoid Leguminosae,this mechanism provides a guard against premature selling. Thesecretory cells are elongated; they remain in communicationthrough persistent pit-fields as the intercellular spaces fillwith secretion product. The secretion forms a lipid-rich emulsion,with a mucilaginous aqueous phase which reacts cytochemicallyfor protein and carbohydrate and has esterase activity. Duringthe early development of the stigma head, the cells possessa fine-structure appropriate to their secretory function, withabundant ribosomal and smooth endoplasmic reticulum, stratifiedor in the form of ramifying and anastomosing tubules, numerousmitochondria and a well developed Golgi system. Lipid globuli,partly invested in endoplasmic reticulum, are abundant in theyoung cells, but there is as yet no indication of how the lipidis transferred to the intercellular spaces during the secretoryperiod. As the stigma matures, the secretory cells become moribund. Leguminosae, Trifolium pratenseL., pollen-stigma interaction, self-incompatibility, autofertility, stigma secretory system, lipid secretion, cuticle permeability