Structure and Development of Plastids in Epidermal Cells of African Violet (Saintpaulia ionantha Wendl.) in Culture

The structure of plastids in epidermal cells of African violet(Saintpaulia ionantha Wendl.) ‘Marge Winters’ wasexamined using transmission electron microscopy before and afterplacement of leaf tissue in culture. The plastids from matureepidermal cells contained membrane-bound inclusion bodies andprolamellar bodies in various stages of development. Starchgrains and poorly developed granal stacks were observed in asmall number of plastids. After placement of the leaves on suitableculture medium, inclusion bodies decreased in size and the lamellarsystem became more organized. The plastids in the epidermaltissue are believed to be in an arrested state of developmentand are released from this state by placement on a medium inductiveto organogenesis. Saintpaulia ionantha Wendl., African violet, membrane-bound inclusion, tissue culture, plastid 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     

A Stereological Analysis of the Succulent Tissue 5Opuntia ficus-indica (L.) Mill.: I. DEVELOPMENT OF MUCILAGE CELLS

A correlated stereological and developmental analysis of thesucculent tissue of Opuntia ficus-indica was carried out. Thestereological parameters related to mucilage cells were describedas a function of their distance from the apical meristem. Polynomesof the second and third degree were found to describe the developmentalprocess. Three zones of development could be distinguished.The relation of the structure of the tissue to its physiologicalfunction and mucilage secretion is discussed.     

Aspects of the Differentiation of the Egg of the Moss Physcomitrium coorgense Broth

Oogenesis in Physcomitrium coorgense follows the course seenin lower archegoniates generally. However no evidence was foundof cytoplasmic autophagy, or, during maturation of the egg,of nucleo-cytoplasmic interaction of the kind reported in liverwortsand ferns. The internal lamellar system of the plastids dedifferentiatesalmost entirely, and there is a corresponding increase in thefrequency of osmiophilic droplets. Starch also disappears, andsimultaneously large quantities of mucilage appear in the cytoplasm.The mucilage is secreted into the venter of the archegoniumand envelopes the egg. The egg lacks a special osmiophilic membrane.     

A Histochemical Study of Nectaries of Hibiscus rosa-sinensis

Different histochemical and cytochemical methods were employedon nectaries of Hibiscus rosa-sinensis. Light microscopy revealedthe presence of oil and mucilage cells in the subglandular tissue.Electron microscopy showed intense activity of ATPase in thephloem subtending the nectary. When CaCl₂ or tannic acid areadded to the fixative, electron-dense globular deposits areencountered in close contact with the plasmalemma of the secretorycells. In this case the endoplasmic reticulum appears in alternatingelectron-dense areas. In young nectaries the application oftannic acid results in electron-opaque deposits at the cellplate of dividing cells. The prolonged incubation of nectariesin OsO₄ results in an obvious difference in staining betweennectary hairs and subglandular cells. Structures stained selectivelywith OsO₄ are the endoplasmic reticulum, nuclear envelope, plastids,and mitochondria. The cytochemical experiments support the viewthat in nectaries of Hibiscus rosa-sinensis, the pre-nectaroriginates from the phloem and it is symplastically carriedvia the plasmodesmata to the secretory cells of the hair fromwhere it is secreted. The principal element which is involvedboth in the pre-nectar transport and nectar secretion is theendoplasmic reticulum. Key words: Lipid staining, polysaccharides, tannic acid, calcium binding sites, ATPase activity, osmium impregnation     

Cortical microtubules mark the mucilage secretion domain of the plasma membrane in Arabidopsis seed coat cells

During their differentiation Arabidopsis thaliana seed coat cells undergo a brief but intense period of secretory activity that leads to dramatic morphological changes. Pectic mucilage is secreted to one domain of the plasma membrane and accumulates under the primary cell wall in a ring-shaped moat around an anticlinal cytoplasmic column. Using cryofixation/transmission electron microscopy and immunofluorescence, the cytoskeletal architecture of seed coat cells was explored, with emphasis on its organization, function and the large amount of pectin secretion at 7 days post-anthesis. The specific domain of the plasma membrane where mucilage secretion is targeted was lined by abundant cortical microtubules while the rest of the cortical cytoplasm contained few microtubules. Actin microfilaments, in contrast, were evenly distributed around the cell. Disruption of the microtubules in the temperature-sensitive mor1-1 mutant affected the eventual release of mucilage from mature seeds but did not appear to alter the targeted secretion of vesicles to the mucilage pocket, the shape of seed coat cells or their secondary cell wall deposition. The concentration of cortical microtubules at the site of high vesicle secretion in the seed coat may utilize the same mechanisms required for the formation of preprophase bands or the bands of microtubules associated with spiral secondary cell wall thickening during protoxylem development.     

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     

Subcellular Localization of Adenylate Cyclase in the Shoot Apices of Bryum argenteum Hedw

Adenylate cyclase activity has been detected in the shoot apicesof Bryum argenteum at the ultrastructural level, using adenylylimidodiphosphate as substrate. Heavy deposits of the reactionproduct were observed along the plasma membrane, tonoplast andthe membranous system of developing plastids. No clear stainingwas associated with other subcellular membranes. Mosses, adenylate cyclase, Bryum, cyclic AMP     

Ultrastructure of the Resin Ducts of Mangifera indica L. (Anacardiaceae). 3. Secretion of the Protein-polysaccharide Mucilage in the Fruit

Mango fruit ducts secrete a protein-carbohydrate mucilage inaddition to lipophilic material. This mucilage is secreted inspecial duct regions. Loops of ER elements seem to delimit cytoplasmicportions rich in ribosomes forming pseudo-vacuoles which eventuallybecome bound by a single membrane of ER origin. It is suggestedthat the protein is produced and accumulates in the pseudo-vacuoleswhich become storage bodies. Carbohydrates are added to thecontent of these bodies by Golgi vesicles. The cytoplasm becomesosmiophilic and contracts before disintegration, and the mucilagepasses into the space between plasmalemma and cell wall. Afterthe cell breaks down the mucilage is released into the ductcavity. Mangifera indica L., mango, Anacardiaceae, resin ducts, secretion, mucilage, ultrastructure     

Anthraquinones and β-polysaccharides content and distribution in Aloe plants grown under different light intensities

The curative and therapeutic effects of Aloe plants have mostly been ascribed to anthraquinones such as aloin, and to some characteristic β-polysaccharides. Although the actual concentration of these bioactives in Aloe plants has not yet been fully clarified, it was expected that plant species, age and growth conditions would play an important role. The aim of this work was to investigate the relationship between species, light intensity and the content of bioactives in Aloe arborescens Mill. and Aloe vera (L.) Burm.f.Aloin was determined by liquid chromatography tandem mass spectrometry: Its concentration was higher in the leaves of younger plants and there was more in A. vera than in A. arborescens. The content of β-polysaccharides was determined colorimetrically after binding with Congo Red dye. The results were not affected by plant age, and concentrations were higher in A. vera than in A. arborescens.Finally, even though the type of tunnel (and therefore light spectrum) under which plants were grown seemed to have no effect on the content of bioactives, the plants grown under reduced light intensities had significantly lower aloin and β-polysaccharides concentrations.     

Determination of aloenin,barbaloin and isobarbaloin in Aloe species by micellar electrokinetic chromatography

Aloenin, barbaloin and isobarbaloin in JP Aloe¹, Aloe barbadensis (Aloe vera) and Aloe arborescens Miller var. natalensis Berger (Aloe arborescens Miller) were determined by micellar electrokinetic chromatography (MEKC) with 50 mM sodium dodecyl sulfate. Aloenin, barbaloin and isobarbaloin were well separated by MEKC and as little as 5.5 pg/11 nl of the three compounds could be detected. The determination took around 14 min.     

Leaf Structural Peculiarities in Sarcopoterium spinosum, a Seasonally Dimorphic Subshrub

Extensive investigations on the anatomy of the two leaf typesin a seasonally dimorphic subshrub revealed interesting variationsbetween summer and winter leaves. Summer leaves of Sarcopoteriumspinosum possess a thick epidermis composed of tannin-containingcells and large amounts of mucilage secreted through the innerpericlinal walls towards the mesophyll. A thick cuticle is alsopresent on the surface of the leaf. In winter leaves the epidermalcells produce no mucilage while phenolics are accumulated ingranular form only. Besides these, some other variations betweensummer and winter leaves are also discussed in respect of theability of the plant to withstand the unfavourable Mediterraneanconditions. Seasonal dimorphism, leaf anatomy, Sarcopoterium spinosum     

Comparative account of nectary structure in Hexisea imbricata (Lindl.) Rchb.f. (Orchidaceae)

• Background and Aims Despite the number of orchid speciesthat are thought to be pollinated by hummingbirds, our knowledgeof the nectaries of these orchids is based solely on a singlespecies, Maxillaria coccinea (Jacq.) L.O. Williams ex Hodge.Nevertheless, it is predicted that such nectaries are likelyto be very diverse and the purpose of this paper is to comparethe nectary and the process of nectar secretion in Hexisea imbricata(Lindl.) Rchb.f. with that of Maxillaria coccinea so as to beginto characterize the nectaries of presumed ornithophilous Neotropicalorchids. • Methods Light microscopy, transmission electronmicroscopyand histochemistry were used to examine the histology and chemicalcomposition of nectary tissue and the process of nectar secretionin H. imbricata. • Key Results and Conclusions The nectary of H. imbricatahas a vascular supply, is bound by a single-layered epidermiswith few stomata and comprises two or three layers of subepidermalsecretory cells beneath which lie several layers of palisade-likeparenchymatous cells, some of which contain raphides or mucilage.The secretory cells are collenchymatous and their walls havenumerous pits with associated plasmodesmata. They contain thefull complement of organelles characteristic of secretory cellsas well as intravacuolar protein bodies but some of the secretoryepidermal cells, following secretion, collapse and their anticlinalwalls seem to fold. Nectar secretion is thought to be granulocrineand, following starch depletion, lipid droplets collect withinthe plastids. The nectar accumulates beneath the cuticle whichsubsequently forms swellings. Finally, nectar collects in thesaccate nectary spur formed by the fusion of the margins ofthe labellum and the base of the column-foot. Thus, althoughthe nectary of H. imbricata and M. coccinea have many featuresin common, they nevertheless display a number of important differences.     

Changes in Plastidic and Cytoplasmic Pyruvate Kinase Activity during Chloroplast Development of Pea in Blue and Red Light

Pyruvate kinase (PK) activity was demonstrated in the cytosolas well as in the plastids of pea leaves. Etioplasts and chloroplastscontained about 12% of the total activity. The presence of PKactivity in different cellular compartments and the pronounceddifferences in kinetic and regulatory properties indicate thatthese activities are due to isoenzymes. When etiolated pea leaves were illuminated with weak blue light,the plastidic PK activity increased immediately, reaching amaximum (about 21% of the total activity) after 24 h of illumination.Under red light, there was a lag period of about 4 h beforethe increase in isoenzyme activity. After 24 h of illumination,however, it reached the maximum found with blue light. In contrast,light quality had no appreciable effect on cytoplasmic PK andphosphoenolpyruvate carboxylase. Increases in NADP-dependent glyceraldehyde 3-phosphate dehydrogenaseactivity and in the soluble protein in the plastids were somewhathigher, whereas the increase in chlorophyll content was slightlylower under blue light than under red light. Blue light specificallyincreased the chlorophyll alb-ratio. These different responsesto the light quality during chloroplast development indicatethat more than one photoreceptor is involved in these processes. The results obtained for pea PK also are discussed in comparisonwith similar findings for the chlorophyll-free Chlorella mutantno. 20. (Received January 19, 1982; Accepted April 21, 1983)     

The Supramolecular Organization of Red Algal Vacuole Membrane Visualized by Freeze-fracture

The supramolecular organization of the vacuole membrane (orof the membranes of mucilage sacs) in 27 species of red algaeis studied in replicas of rapidly frozen and fractured cells.Intramembranous particle complexes composed of four particles('tetrads' with average diameters between 8·5 and 14·5have been observed in the protoplasmic fracture (PF) face butmost clearly and more frequently in the exoplasmic fracture(EF) face of the vacuole membrane of all red algae investigated.The tetrads lie individually within the vacuole membrane orform clusters in several species and are randomly distributed.In the species Ceramium diaphanum var. strictum and Laurenciaobtusa the intramembranous particle complexes ('tetrads') havebeen observed both in the EF and PF faces of the vacuole membrane;the 'membrane tetrads' at least as regards these two speciesseem to span both the outer and inner leaflets of the vacuolemembrane ('transmembrane particles'). The occurrence of particletetrads in the plasma membrane is probably due to exocytosiseither of the Golgi vesicles or of the mucilage sacs. Tetradfrequency in the EF face of the vacuole membranes of the investigatedred algae varies between 2 and 87 µm^-2, while that ofsingle particles varies between 102 and 695 µm^-2. ThePF face of the vacuole membrane is characterized by a higherparticle density than the EF face. The particle densities ofthe PF and EF faces of the plasma membrane for a given speciesare higher than those of the corresponding fracture faces ofthe vacuole membrane. Some members of Bangiophycidae bear smallerprotein particles (diameter between 8·5 and 10·5nm) in comparison with those of Florideophycidae (diameter between10·5 and 14·5 nm). It is suggested, based uponthe particle tetrads lying in depressions of the vacuole membraneand the origin of vacuoles (mucilage sacs) from ER, that theparticle tetrads originate from the ER or the Golgi complex.Since vacuoles (mucilage sacs) in red algae, along with theGolgi complex, are involved in the synthesis and export of cellsurface polysaccharides, it could be assumed that the 'membrane-tetrads'within the vacuole membrane represent a membrane-bound multienzymecomplex, participating in the synthesis of amorphous extracellularmatrix polysaccharides.Copyright 1993, 1999 Academic Press Red algae, freeze-fracture, vacuole membrane, mucilage sacs, membrane tetrads, supramolecular organization     

Serial Development of Foliar Gemmae in Tortula (Pottiales, Musci), an Ultrastructural Study

The development and liberation mechanism of foliar gemmae havebeen studied by electron microscopy in two mosses, Tortula latifoliaBruch and Tortula papillosa Wils. The gemmae develop on theadaxial surface of mature leaves from single initial cells onboth the lamina and costa in T. latifolia but only on the costain T. papillosa . Elongation of the initial cell is associatedwith the deposition of a highly extensible new wall whilst theold wall and cuticle in the apical dome rupture. The first divisionis transverse and separates a short basal cell embedded in thefoliar tissue and a distal cell, or gemma primordium, protrudingfrom the leaf surface. Subsequent divisions of the gemma primordiumgive rise to a six-to-eight-celled globose gemma with mucilaginousouter walls. During gemma development the basal cell producesa new wall and elongates again whilst the common wall with thegemma splits apart centripetally along the boundary betweenthe old and new wall in the basal cell; plasmodesmal connectionsare gradually severed and eventually the young gemma remainsconnected to the basal cell only by mucilage. After separationof the first-formed gemma, the basal cell may expand and producea second gemma by the same mechanism. The whole process maybe repeated several times resulting in the formation of a chainof gemmae stuck together by mucilage and which are liberatedonly when the leaves are fully hydrated. Accumulation of abundantlipid deposits in the gemmae after symplasmic isolation reflectsconsiderable photosynthetic autonomy. Abscission; bryophytes; cell wall formation; plasmodesmata; vegetative reproduction     

Leaf Development in Lolium temulentum: Formation of the Photosynthetic Apparatus in the Presence of the Porphyrin Synthesis Inhibitor Gabaculine

Gabaculine, a potent inhibitor of the biosynthesis of aminolaevulinicacid in plants, was supplied via the roots to seedlings of Loliumtemulentum and chloroplast development along the age gradientof the emergent leaf was followed. Exposure to the inhibitorprevented the development of an organized photosynthetic membranesystem and a noticeable accompanying feature was the appearanceof aggregates of osmiophilic globules even in young plastids.In untreated leaves these were only seen to any extent in chloroplastsundergoing senescence. Though chlorophyll formation was inhibitedby gabaculine, levels of carotenoid in treated tissue were somewhatelevated. However, there was a selective depletion ofß-carotenewhich, in situ, is closely associated with the photosyntheticreaction centre. Amounts of two plastid-localized tetrapyrrole-bindingproteins, light-harvesting chlorophyll protein of photosystem-2(LHCP-2) and cytochrome f, were determined. There was a closecorrespondence in inhibition between LHCP-2 and its prostheticgroup with the greatest decrease, compared to leaves of untreatedplants, being at the leaf base. In contrast, formation of theapoprotein and haem components of cytochrome f was apparentlynot so tightly coupled. Amounts of apoprotein were similar tothose of untreated controls, but haem was concentrated in theregion proximal to the base and declined along the age gradient,being absent from the leaf tip. Appearance of novel haem-peroxidaseactivities in the basal region of treated leaves was observed. Key words: Lolium temulentum, gabaculine, chlorophyll, LHCP-2, cytochrome f.     

Ultrastructure of Resin Ducts in Pinus halepensis Development, Possible Sites of Resin Synthesis, and Mode of its Elimination from the Protoplast

Development of the resin duct cavity, sites of resin synthesisin the epithelial cells and elimination of resin from the protoplastwere studied in roots of young Pinus halepensis seedlings. Itis suggested that the Golgi bodies are involved in dissolutionof the middle lamella in the region of the future duct cavityby secretion of lytic enzymes into the cell walls. In earlystages of duct development osmiophilic droplets were observedin plastids, periplastidal and cytoplasmic ER, Golgi vesicles,mitochondria, nuclear envelope and in the cytoplasm. In thelatter they were often observed to be surrounded by a membrane.Electron micrographs suggested that elimination of resin dropletsfrom the protoplast occurs by their becoming surrounded by plasmalemmainvaginations.