Studies on Differentiation of Laticifers through Light and Electron Microscopy in Calotropis gigantea (Linn.) R.Br.

The distribution, cytological organization and differentiationof non-articulated laticifers in the primary and mature tissuesof Calotropis gigantea (Linn.) R.Br., were studied by the useof optical and electron microscopy. Laticifers occur in thecortex, vascular bundle and pith of the plant axis. At the earliestdetectable stage a laticifer is a cell which undergoes rapidelongation and nuclear division. This results in a multinucleateelongated cell which undergoes further increase in length withgradual degeneration of the cytoplasm. At the electron microscopiclevel the presumptive laticifer cell shows increasing vacuolationwhich forms a large central vacuole. Simultaneously the cytoplasmicorganelles undergo degeneration by autophagic processes. Laternumerous vesicles can be observed in the large central vacuole,the remaining cytoplasm being pushed to a thin layer. Maturelaticifers show three types of spherical structures of whichthe highly electron dense globules are the latex particles. Calotropis gigantea (Linn.), R.Br., laticifers, ultrastructure, differentiation     

LATICIFER ULTRASTRUCTURE AND DIFFERENTIATION IN SEEDLINGS OF PAPAVER BRACTEATUM LINDL., POPULATION ARYA II (PAPAVERACEAE)

Laticifers of Papaver bracteatum Lindl., population Arya II, seedlings were examined by electron microscopy. Laticifers were first differentiated in procambium of the radicle associated with phloem about 72 hr after seeds were sown. Proliferation of membrane-bound vesicles of apparent endoplasmic reticulum origin distinguished laticifers from adjacent cells. Vesicles developed electron-dense caps from the internal condensation of small particles. Laticifer initials possessed the usual complement of organelles that became obscured in mature cells by the large, closely packed vesicles. Plastids contained an electron-dense, membrane-bound inclusion, but never developed lamellae or starch grains. Articulation and anastomoses between laticifer elements resulted from gradual removal of wall materials by both cells on opposite sides of the common walls at a perforation site. Differentiation of the laticifer initials and the micromorphology of the protoplast of P. bracteatum is similar to that reported for P. somniferum.     

Developmental Features of Cell Wall Formation in Sieve Elements of the Grass Aegilops comosa var. thessalica

In differentiating sieve elements of Aegilops comosa var. thessalicadictyosomes are abundant and they produce numerous smooth vesicles.Coated vesicles seem to bud from smooth ones. Since both kindsof vesicles appear both in the cytoplasm and in associationwith the plasmalemma, it is proposed that they move to and fusewith the plasmalemma transferring products for cell wall synthesis.During differentiation sub-plasmalemmal microtubules are initiallyscarce and randomly oriented but soon afterwards they becomenumerous and transversely oriented to the long axis. Cellulosemicrofibrils in the cell wall appear to run parallel to themicrotubules and the latter may regulate microfibril orientation. Root protophloem sieve elements develop wave-like wall thickenings,which are, during development, overlaid by microtubules perpendicularto the long axis. Just after maturation these thickenings progressivelybecome smooth and finally the walls appear uniform in thickness.The wave-like wall thickenings may function as stored wall material,utilized in later stages of development when wall material willbe needed and its synthesis will be impossible because of theabsence of a synthesizing mechanism in the highly degraded protoplastsof mature sieve elements. It is suggested that in this way thethickenings may enable root protophloem sieve elements to growand keep pace with the active clongation of the surroundingcells. Aegilops comosa var. thessalica, sieve elements. cell wall, microtubules, dictyosomes, coated vesicles, wave-like thickenings     

Developmental regulation of benzylisoquinoline alkaloid biosynthesis in opium poppy plants and tissue cultures

Summary Opium poppy (Papaver somniferum L.) contains a number of pharmaceutically important alkaloids of the benzylisoquinoline type including morphine, codeine, papaverine, and sanguinarine. Although these alkaloids accumulate to high concentrations in various organs of the intact plant, only the phytoalexin sanguinarine has been found at significant levels in opium poppy cell cultures. Moreover, even sanguinarine biosynthesis is not constitutive in poppy cell suspension cultures, but is typically induced only after treatment with a funga-derived elicitor. The absence of appreciable quantities of alkaloids in dedifferentiated opium poppy cell cultures suggests that benzylisoquinoline alkaloid biosynthesis is developmentally regulated and requires the differentiation of specific tissues. In the 40 yr since opium poppy tissues were first culturedin vitro, a number of reports on the redifferentiation of roots and buds from callus have appeared. A requirement for the presence of specialized laticifer cells has been suggested before certain alkaloids, such as morphine and codeine, can accumulate. Laticifers represent a complex internal secretory system in about 15 plant families and appear to have multiple evolutionary origins. Opium poppy laticifers differentiate from procambial cells and undergo articulation and anastomosis to form a continuous network of elements associated with the phloem throughout much of the intact plant. Latex is the combined cytoplasm of fused laticifer vessels, and contains numerous large alkaloid vesicles in which latex-associated poppy alkaloids are sequestered. The formation of alkaloid vesicles, the subcellular compartmentation of alkaloid biosynthesis, and the tissue-specific localization and control of these processes are important unresolved problems in plant cell biology. Alkaloid biosynthesis in opium poppy is an excellent model system to investigate the developmental regulation and cell biology of complex metabolic pathways, and the relationship between metabolic regulation and cell-type specific differentiation. In this review, we summarize the literature on the roles of cellular differentiation and plant development in alkaloid biosynthesis in opium poppy plants and tissue cultures.     

Ultrastructure and Development of the Laticifers of Ficus carica L

Laticifers of Ficus caricaL. are of the branched, non-articulatedtype. They occur in the cortex and pith of the plant axis andpenetrate leaves and inflorescences. Observations were madeon laticifers located in shoot apices. Growing regions of laticifers undergo a sequence of ultrastructuralchanges. These are: (a) a pronounced increase in the vacuolarspace which divides the cytoplasm into separated masses; (b)a development of numerous vesicular structures in the cytoplasm.The vesicular structures are released into the vacuolar space.The whole process is accompanied by disintegration of cytoplasm.Apparently isolated masses of cytoplasm occur in the luminaof laticifer tips in sections taken from dormant apices. Itis assumed that these masses have a role in the initiation ofnew laticifer regions in the next growing season. Ficus caricaL., laticifers, ultrastructure, development differentiation     

Observations on the Internal Structure of the Spermatozoid of Dictyota

The spermatozoid of Dictyota is shown to be structurally morelike a vegetative zoospore than was the case in Fucus. The mitochondria,golgi, overall shape of the nucleus, nuclear membrane, fat bodies,and miscellaneous vesicles are as in a zoospore; there is, however,a vestigial chromatophore without an eyespot and the ciliaryapparatus is specialized. In spite of the single flagellum thereare two basal bodies inside the cell, one of which is apparentlyvestigial, ending blindy in the cytoplasm; both the a similarinternal structure with nine fibres in the wall. A fibrous ‘root’,possibly homologous with the ‘proboscis’ of Fucus,arises near the outer side of the functional basal body; itis a band of about eight fibres passing through the cell withouttouching the nucleus but closely pressed to the inner facesof at least two mitochondria before ending in an unknown mannerat the cell surface. The internal structure of the flagellumis normal but the fact that the median strand is marked by arowspines has been used to demonstrate is a conclusive way thefacts of bilateral symmetry in the whole organ; Dictyota agreesexactly with Fucus and a previous error based on incompleteinformation has been corrected. The process of unwinding ofthe flagellum from the surface of the body after liberationfrom the antheridium is described and used to illustrate someunexpected properties of the surface membrane.     

The Ultrastructure of the Alkaloidal Vesicles of Papaver somniferum latex

Papaver somniferum latex contains abundant small vesicles. Theirultrastructure was studied in tissue sections from adult plantsand in sections of sequential fractions of centrifuged latex.The vesicles were found to exist in two forms, the first witha smooth but progressively granulated outer membrane and thesecond, probably derived from the first, with adherent ‘cap-like’structures which in the heavier centrifuged fractions possesseda zonally-ordered interior. These vesicle fractions were active in synthesizing morphineand the name ‘alkaloidal vesicle’ is proposed forthem. Papaver somniferum latex also contains an organelle whichwas found to resemble a complex organelle present in the latexof Hevea brasiliensis. Its function is not yet known.     

IDENTIFICATION OF LATICIFERS IN EMBRYOIDS DERIVED FROM CALLUS AND SUSPENSION CULTURES OF ASCLEPIAS SPECIES (ASCLEPIADACEAE)

Laticifers were identified in frozen sections of embryoids from callus and suspension cultures of Asclepias syriaca (common milkweed) by an indirect fluorescent antibody technique. Sections were treated with the IgG fraction of rabbit anti-latex antiserum, produced with field-collected A. syriaca latex as a source of antigens, and with fluorescein-conjugated IgG fraction goat anti-rabbit IgG. Laticifers were identified by their fluorescence in embryoids dissected from 3–4-month-old callus cultures and in embryoids from 2-month-old suspension cultures. Laticifers are not present in early globular embryoids of A. syriaca but embryoids similar in shape to late globular stage zygotic embryos possess branching laticifers typical of zygotic material. Sections on control slides, treated with whole serum or IgG fraction from whole serum, both from an uninjected rabbit, contained no fluorescent cells. No laticifers were detected with the fluorescent antibody assay in A. tuberosa embryoids.     

Polysaccharide Secretion by the Watermelon Stigma

Secretion of the galactose-containing polysaccharide componentof the watermelon stigma exudate was studied using electronmicroscopy cytochemistry and autoradiography. Polysaccharidelocalization using the thiosemicarbazide–silver proteinatemethod stained the Golgi apparatus and secretory vesicles, thecell wall, wall thickenings and extracellular secretion. Thesame result was obtained at anthesis and at 18 h prior to anthesis,which coincides with the period of maximum secretion. Labellingof stigmas in vivo with D-(1-³H) galactose at 20 h prior toanthesis resulted in different labelling patterns after 2 h(18 h prior to anthesis) and 20 h (anthesis). At 18 h priorto anthesis label was present in the Golgi apparatus and secretoryvesicles, the cell wall and wall thickenings. By anthesis labelhad accumulated in the extracellular secretion in addition tothe Golgi apparatus, secretory vesicles, cell wall and wallthickenings. The results suggest that the polysaccharide componentof the stigma exudate is produced in the Golgi apparatus andsecreted via the cell wall and wall thickenings. Citrullus lanatus Thumb., Matsum and Nakai, watermelon, autoradiography, stigma, secretion, cytochemistry, polysaccharide     

Ion Fluxes to the Vacuole of Nitella translucens

The time course of the appearance in the vacuole of Nitellatranslucens and of Tolypella intricata of tracer from the outsidesolution has been studied over short periods of uptake. Thereare two components of chloride transfer to the vacuole, a fastcomponent linear with time and a second component at longertimes whose behaviour is reasonably well described in termsof a single rate constant for exchange; a constant fractionof the total entry is in the fast component and the apparentrate constant for the second component is proportional to theinflux. In Nitella the path of rapid transfer involves chlorideand sodium, and may also involve a small but variable amountof potassium, but in Tolypella potassium has a significant componentof rapid transfer; these correspond to the cations for whichchloride-linked components of cation influx have been shownby another worker. Over both parts of the time course the level of activity inthe cytoplasm specifies, not the rate of transfer to the vacuoleas would be expected, but the rate as a fraction of the influx;the processes of influx to the cell and transfer to the vacuoleare intimately linked. It is difficult to explain the results in terms of static membranesand fixed compartments. An explanation in terms of the sequence,entry of salt by pino-cytotic vesicles at the plasmalemma, fusionof these vesicles with the endoplasmic reticulum after someloss of tracer to the surrounding cytoplasm, and transfer tothe vacuole in minivacuoles formed from the endoplasmic reticulum,is consistent with the time course found. A model of this kind,involving transport by a dynamic membrane system, seems necessaryto explain the results.     

The Ultrastructure of Tetrasporogenesis in the Marine Red Alga Chondria tenuissima (Good, et Woodw.) (Ceramiales, Rhodomelaceae)

Tetraspore development has been studied in Chondria tenuissimausing light and electron microscopy. The transformation of tetrasporangialmother cells into mature tetrasporangia involves a series ofstructural changes, especially of dictyosomes and of the nucleus.The youngest stage of tetrasporogenesis consists of a uninucleatetetraspore mother cell with synaptonemal complexes present duringearly prophase of meiosis I. Mitochondria are aggregated aroundthe nucleus, dictyosome activity is low, and proplastids occurin the peripheral cytoplasm. The cleavage furrows are initiatedalmost concomitantly with commencement of meiosis. When thecleavage furrows are initiated, spherical bodies bounded bytwo membranes are found within the cytoplasm; they develop intovacuoles with fibrillar contents (fv₁), which increase in sizeduring tetraspore development by fusing with each other andwith Golgi vesicles. The Golgi vesicles and the vacuoles withfibrillar contents (fv₁) contribute material to the developingtetraspore wall. During the middle stage of tetraspore formationthe vacuoles with fibrillar contents (fv₁) are dominant, dictyosomeactivity increases, as well as the number of plastids and mitochondria;starch formation also increases. Stacked cisternae of the endoplasmicreticulum are found within the peripheral part of the nucleus.The same nuclear structures are also observed in tetrasporangiaof the marine red alga Gastroclonium clavalum. The final stageis characterized by the disappearance of vacuoles with fibrillarcontents (fv₁) and of the stacked ER within the nucleus, presenceof straight, large dictyosomes which produce cored vesicles,an abundance of starch grains and by the formation of fullydeveloped chlorqplasts. The cored vesicles contain Thiéry-positivematerial and contribute to the formation of vacuoles with fibrouscontents (fv₂) as they are dominant in the tetraspores beforetheir liberation. Rhodophlyla, Chondria, tetrasporogenesis, ultrastructure, Golgi apparatus     

A Fine Structural Analysis of Auxin-induced Elongation of Cucumber Hypocotyls, and the Effects of Calcium Antagonists and Ionophores

The fine structure of epidermal cells, particularly in relationto dictyosomes, has been examined in different regions of dark-growncucumber hypocotyls and in response to auxin treatment, usingboth dot overlay and image analysis techniques. The most noticeablechange in cell structure along the hypocotyls is the increasein vacuolar volume. The volume fraction occupied by dictyosomesand secretory vesicles also increased, whereas that for mitochondriaremained relatively constant. During auxin treatment, the volumefraction for dictyosomes showed an increase after 30 min followedby a fall, whereas that occupied by secretory vesicles fellsteadily over 90 min. The number of cisternae per dictyosomeshowed some increase after 2 h of auxin treatment, althoughthe increase in dictyosomal material with cell expansion waslargely accounted for by an increase in the number of dictyosomes. Auxin-stimulated elongation growth of the hypocotyls was inhibitedby a range of calcium antagonists, chelators and ionophores.The most marked inhibitions were observed with calcium chloride,the chelator chlortetracycline and the ionophores verapamil,nigericin and monensin. Linear transducer experiments showedthat these compounds generally caused an immediate reductionin the rate of growth. Fine structural observations carriedout on epidermal cells showed the most obvious effects withmonensin and nigericin which caused dictyosomes and secretoryvesicles to swell. EGTA and LaCl₃ caused secretory vesiclesto accumulate around dictyosomes, while the ionophore A23187had little effect. The results suggest that the concentration of Ca²⁺ in the cytoplasmmay be critical for cell elongation. Compounds which chelateCa²⁺ appear to be more effective inhibitors of growth in theinitial acid-induced phase, whereas those which affect ionicgradients are more disruptive in the second phase.Copyright1993, 1999 Academic Press Calcium, Cucumis sativus hypocotyle, dictyosomes, elongation growth, indoleacetic acid, stereology     

Opaline gland ultrastructure in Aplysia californica (Gastropoda: Anaspidea)

Secretions released from the ink and opaline glands of Aplysiacalifornica protect this shell-less mollusc from predators inseveral ways; the most recently discovered, phagomimicry, stimulatesthe feeding behaviours of the predator, distracting it fromthe sea hare. The structure of the ink gland has been reported,but little is known about the opaline gland. This paper comparesthe structure of the opaline gland of A. californica with thatof its ink gland, as well as two additional vesicle types foundin the epidermis. The opaline gland consists of single largecells, the vesicle cells, each with an enlarged nucleus, themaximum size of both exceeding that of respective structuresin the ink gland. Opaline vesicles, like ink vesicles, are enclosedby an external layer of muscle. Opaline vesicles, unlike inkvesicles, are not immersed in additional cells, but are freewithin the haemolymph and are, therefore, the probable sitefor the synthesis of their protein contents. The necks of individualopaline vesicles are fused into a central canal, but short necksconnecting each vesicle to the central canal remain; these arefilled with epithelial cells, but lack a muscular release valvelike that in the long necks of ink vesicles. Mucous cells containcircular arrays and are structurally distinct from opaline vesicles;mucous cells, though enlarged, are smaller than opaline or inkvesicle cells; they lack an external layer of muscle and a multicellularneck and, therefore, more closely match another vesicle typein the skin of A. californica, the white vesicle, which is involvedwith excess calcium excretion. (Received 22 September 2006; accepted 20 March 2007)     

New Ideas on Amphibian Immunity: The Lymph Gland: A Generator of both T and B Cells

Anuran amphibian larvae of the genus Rana possess three majorlymphoid organs: the thymus, the lymph gland, and the spleen.Other accumulations of lymphocytes are present in the kidney,liver, and intestine. The thymus develops lymphocytes firstfollowed by peripheral differentiation of other lymphoid centers.Since bone marrow is absent in larvae, there must be an alternativesource of stem cells that differentiate into T cells under thymicinfluence or B cells under the influence of some other organ(s).We are concerned with the source of B cells after bullfrog larvaebecome immunologically mature. Such an organ should possessstem cells, and, to qualify further, it should play a majorrole in antibody synthesis. The lymph gland seems to fulfillthis requirement. Contrary to our expectations, lymph glandscan restore not only antibody synthesis but also transplantationimmunity in a significant number of larvae. Thus, the lymphgland may house stem cells that can differentiate into B cellsand T cells.     

Mucilage Cells, Calcium Oxalate Crystals and Soluble Calcium in Opuntia ficus-indica

The subcellular location of soluble calcium in parenchymatousand mucilage cells of Opuntia ficus-indica was determined histochemically.Soluble calcium was observed in crystal chambers containingcalcium oxalate on the membrane of the vesicles. Calcium wasalso present in the plasmalemma, in plasmodesmata, in cell walls,in mitochondria and in the vacuoles. Especially marked was thepresence of soluble calcium in vesicles free or fused with theplasmalemma. Little free calcium was observed in other cellcompartments. In the calcium economy of tissues the location of soluble calciumand the transport of calcium to and from mucilage cells to parenchymatouscells and calcium oxalate idioblasts will play a role. Chelationof calcium by mucilage or oxalate, which depends on pH, ionicstrength, etc., will be important in this respect. Opuntia ficus-indica, calcium oxalate, mucilage cells, transport of calcium     

Structure and Function in the Grass Ligule: the Endomembrane System of the Adaxial Epidermis of the Membranous Ligule of Lolium temulentum L. (Poaceae)

The endomembrane system of the adaxial epidermal cells of themembranous ligule of the grass Lolium temulentum L. has beenstudied by conventional transmission electron microscopy, andby using zinc iodide-osmium tetroxide impregnation with examinationof thick sections at 100 kV. The components of the endomembranesystem are the nuclear membranes, rough endoplasmic reticulum(present in both cisternal and tubular forms), dictyosomes,dictyosome-derived vesicles, coated vesicles, plasma membraneand tonoplast. Direct continuity between tubular endoplasmicreticulum and the cis face of dictyosomes is demonstrated andthe applicability of the endomembrane concept to this putativesecretory tissue is discussed. The presence of vesicle-likeprofiles apparently within the outer tangential walls is reported.Copyright1995, 1999 Academic Press Ligule, Lolium temulentum L., darnel, grasses, Poaceae, Gramineae, endomembrane concept, ultrastructure, zinc-iodide-osmium tetroxide impregnation     

Excitatory Transmission in Insect Neuromuscular Systems

Many, but not all, visceral muscles in insects are innervatedby neurosecretory axons. The neurosecretory junctions with theheart muscle of the American cockroach, Periplaneta americana,show ultrastructural and electrophysiological evidence of chemicallytransmitting synapses, and cytochemical evidence for the presenceof monoamines. Electron microscopy of nerve terminals showsthat synaptic vesicles may be formed directly from electron-dense"neurosecretory" granules Neurotomy of motor axons to skeletal muscles in insects leadsto aggregation and clumping of synaptic vesicles after 48 hours.Treatment of in vitro nerve-muscle preparations with variousrespiratory poisons caused aggregation similar to that developedin neurotomized animals. This suggested that vesicle aggregationin both cases may have resulted from a decrease in availableadenosine triphosphate in the nerve terminal with subsequentalteration in the normal charge density which supports a repulsiveforce between the vesicles.     

Laticifers in stamens of Papaver somniferum L

Summary Articulated anastomosing laticifers were identified at both light and electron microscopic levels in the stamens of Papaver somniferum L. They were observed associated with the phloem forming a continuous system from the filament into the anther of the stamen. Laticifers, which were comparable in structure to laticifers found elsewhere in the plant, possessed numerous vesicles of different sizes within the protoplast.     

On the Occurrence of Spiny Vesicles in the Phloem of Salix

Many parenchyma cells in the primary phloem of young shootsof Salix contain spiny vesicles similar to those reported byNewcomb and others. They may occur singly or clustered, usuallyintermingled with other cell components. A lightly-stainingfibrous-granular background substance is generally found intheir vicinity. In most cells this substance is evenly dispersedin the cytoplasm; less frequently, a presumably similar substanceshowing a tendency to form compact clumps occurs in the vicinityof the spiny vesicles. These clumps occasionally show a tubularorganization, suggesting P-protein. The spiny vesicles are alsofound in association with well developed P-protein bodies insome cells. However, the question as to whether spiny vesiclesare connected with the formation of P-protein is left open.