Light and electron microscopical investigations on shell pores (caeca) of fissurellid limpets (Mollusca: Archaeogastropoda)

The organic content (caecum) of the shell pores of five species of fissurellid (key-hole) limpets was investigated by means of light and electron microscopy. Fissurellid caeca are unbranched, polycellular extensions of the mantle epithelium, which penetrate the whole shell and contact the periostracum via organic fibres called 'brush'. They are built up by two cell-types, which enclose a central lumen, and are formed concurrently with the shell itself. Because of fundamental structural and developmental differences, the superficially similar shell pores of bivalves (caeca) and polyplacophorans (aesthetes) are considered as analogous rather than homologous organs. Similarities are found with brachiopod caeca, probably owing to similar functions.     

Light and electron microscopical observations on the heterotrophic protist Thaumatomastix salina comb. nov. (syn. Chrysosphaerella salina) and its allies

The marine flagellates presently known as the chrysophytes Chrysosphaerella salina and C. tripus Takahashi & Hara have been refound and studied with light microscopy and whole mounts for electron microscopy. Based on material from Australia and Denmark (the latter from the type locality), C. salina is shown to be a colourless protist related to Reckertia sagittifera Conrad. It is characterized by a combination of flagellar features previously thought to be restricted to Reckertia , i.e. a short anterior flagellum which is scale-clad, and a longer, usually posterior but naked flagellum. The scales on the body are shown to be silicified. The new light microscopical studies have also shown considerable resemblance between C. salina, C. tripus and the genus Thaumatomastix Lauterborn. C. salina and C. tripus are therefore transferred to this genus together with Reckertia and the 2 marine species described since 1980 as belonging to Chrysosphaerella, C. triangulata Balonov and C. patelliformis Takahashi & Hara. Thaumatomastix bipartita sp.nov. is illustrated and described.
Chrysosphaerella appears to be a genus of photosynthetic, colony-forming chrysophytes restricted to freshwater habitats. Thaumatomastix is a genus of heterotrophic protists, usually solitary, which occurs in both marine and freshwater environments. The two genera show little, if any, phylogenetic relationship to each other.     

Regeneration of niger (Guizotia abyssinica Cass.) CV Sahyadri from seedling explants

Root, hypocotyl and cotyledonary explants of niger (Guizotia abyssinica Cass) CV. Sahyadri were aseptically cultured on Murashige and Skoog's basal medium (MS) containing BAP and kinetin. Multiple shoot regeneration was induced from hypocotyl and cotyledonary explants while root explants produced only callus on MS medium supplemented with BAP. BAP (1 mg l^-1) was optimum for shoot regeneration. Regenerated shoots were transferred to MS medium without auxins, with auxins and with increasing concentrations of sucrose for rooting. Complete plantlets were obtained in all cases; however, 0.5 mg l^-1 NAA was the best for induction of roots. Ninety-seven per cent of the plantlets survived and completed their life cycle when transferred to natural conditions.Abbreviations BAP 6-benzylamino purine - NAA -naphthaleneacetic acid - IAA indole-3-acetic acid - IBA indole-3-butyric acid     

Intracellular effects on Tetrahymena pyriformis following exposure to preimmune and immune fluids: Light and transmission electron microscopical observations

Nonimmune sera or ascites fluids induce the formation of large and small bodies in the ciliate Tetrahymena pyriformis as seen by light microscopy. Staining indicates that the large bodies are polysaccharide and the small ones lipid. The large bodies generally cannot be identified by transmission electron microscopy, while the small bodies appear to be lipid drops. Immune fluids agglutinate and immobilize the protozoa, which later become ensheathed within an exudate derived from these protozoa. As long as the ciliates remain agglutinated and ensheathed, the large bodies do not appear but do so when the animals leave the clumps and again are swimming freely. The present study is concerned with identifying the large bodies either as food vacuoles or as endocytic vacuoles formed by coalescing food vacuoles and pinocytic vacuoles or as new structures. The addition of latex particles to ciliates exposed to preimmune or immune fluids in the presence or absence of cytochalasin B, a drug which reportedly inhibits food vacuole formation, has not yet allowed the further identification of the large body structures.     

Light and electron microscope observations on Nephroselmis astigmatica sp. nov. (Prasinophyceae)

Nephroselmis astigmatica sp. nov. is described based on light and electron microscope observations of cultured material, originally collected and isolated from the Natal South Coast, Republic of South Africa. It is characterized by (1) large cell size, (2) absence of a stigma, (3) markedly differentiated anterior part of the cell, (4) possessing two types of flagellar scales in addition to hair scales, (5) possessing four types of body scales and (6) the presence of characteristic pit scales in the flagellar pit. Scale morphology was compared with previously described species, and the morphology of spiny (or stellate) body scales thought to be one of the most useful diagnostic characters in delineating species within the genus. The origin of pit scales is discussed and a similar origin for the third layer of flagellar scales of the type species, N. olivacea Stein is suggested. N. astigmatica shares many ultrastructural features with the type species, including the microtubular flagellar root system consisting of three different roots, one of which is multilayered. The validity of this root system as a generic character is suggested.     

Differential growth, physiological and biochemical responses of niger (Guizotia abyssinica Cass.) cultivars to water-deficit (drought) stress

The present study demonstrates the effect of polyethylene glycol-8000 (PEG) and percent field capacity (FC%)-induced water-deficit stress on growth, water status, productivity and various biochemical parameters in Guizotia abyssinica Cass. cultivars (IGP 76, GA 10, No. 71 and IGPN 2004) at seedling and maturity stages of the plant. Cultivar GA 10 showed higher, IGP 76 and No. 71 moderate, and IGPN 2004 least reduction in percent seed germination given PEG stress treatments (0, 10 and 20%). A similar pattern was observed for decreased growth and water content of the seedlings and plants of the cultivars exposed to both kinds of water-deficit stresses. The productivity (number of capitula per plant, number of seeds per capitula and 1,000-seed weight) and total chlorophyll content of cultivar IGPN 2004 was significantly higher in comparison to other cultivars given different FC% treatments (100, 80 and 60%). Significantly higher accumulation of proline, glycine betaine and total soluble sugars and lower damage to membrane lipids under increased water-deficit stress (i.e., at 80 and 60% FC) conditions in cultivar IGPN 2004 suggested its more tolerance capacity to water-deficit stress in comparison to other cultivars. Besides, antioxidant enzyme activities (superoxide dismutase, catalase, ascorbate peroxidase and guaiacol peroxidase) partially demonstrated variations in the tolerance of the cultivars to water-deficit stress. The results suggest that cultivar IGPN 2004 could be considered as more tolerant, and IGP 76 and No. 71 as moderately tolerant, whereas GA 10 was more sensitive to water-deficit stress.     

A scheme of rabbit spermateleosis based upon electron microscopical observations

Summary Rabbit spermateleosis is subdivided into ten stages (A to J) based upon fine structure. Spherical spermatids in stages A to D correspond to the Golgi phase and the cap phase of Leblond and Clermont (1952a). Elongating spermatids in stage E through the first half of stage H correspond to the acrosome phase, and maturating spermatids in the second half of stage H through stage J correspond to the maturation phase. The development of the different organelles during each stage is described and put into a scheme of normal rabbit spermateleosis that can be used as a reference in experimental investigations of ultrastructural changes.This work was supported by grants from Anslaget för främjande av ograduerade forskares vetenskapliga verksamhet vid Veterinärhögskolan.     

Scanning electron microscopical observations on the differentiating mesonephros of the chick embryo

Chick embryos were staged according to the method of Hamburger and Hamilton [1951] and fixed. Cross sections through the cephalic fourth of the mesonephric ridges were examined by scanning electron microscopy. The steps in glomerular differentiation could be observed with ease. The first foot processes to appear in podocytes arose directly from the basal surface of the cell body. In a second step, lateral branches appeared and gave off secondary or even tertiary branches that interdigitated with those from neighbouring podocytes, following a pattern that was very similar to the one previously described by other authors in metanephric nephrons. Endothelial pores appeared in the glomerular capillaries at very early stages of the glomerular differentiation. The differentiation of the epithelium of proximal tubules was characterized by the growth of apical microvilli and of finger-like evaginations from the lateral membranes. At stages 20 and 21, the most differentiated glomeruli had only basal foot processes; only after stage 25 did the first generation nephrons reach full maturity. Because during this period the mesonephros is known to produce urine, our results indicate that nephrons start to function before they have completed their differentiation.     

Light and electron microscopical immunocytochemistry of 5'-nucleotidase in rat cerebellum

5'-Nucleotidase in nervous tissue has so far not been localised at the ultrastructural level using immunocytochemical techniques. We have now applied monoclonal antibodies and a polyclonal antiserum raised against this ecto-enzyme and describe the distribution of 5'-nucleotidase antigenicity in rat cerebellum both at the light and electron microscopic levels. Within all cerebellar layers, 5'-nucleotidase immunoreactivity was found on plasma membranes of glial elements, i.e. Bergmann glial cell processes crossing the molecular layer, astrocytic end-feet around blood vessels and glial cell extensions surrounding single Purkinje cells. In the granular layer, 5'-nucleotidase immunoreactivity was present on glial membranes interposed between granule cells. Neuronal cells or processes were devoid of immunoreactivity. The immunocytochemical results were compared with conventional 5'-nucleotidase histochemistry. Both techniques showed the same ecto-localisation of the enzyme and favour the view of 5'-nucleotidase being predominantly situated at glial plasma membranes.     

In vitro plant regeneration from callus of niger (Guizotia abyssinica Cass.) cv. Sahyadri

Callus formation was achieved with root, hypocotyl, and cotyledon explants of niger (Guizotia abyssinica Cass.) cultivar Sahyadri on Murashige and Skoog medium containing 0.5 mg l^–1 β-indoleacetic acid + 1.5 mg l^–1 6-benzylaminopurine (BAP). Hypocotyl and cotyledon-derived calli when transferred onto a medium with 0.5 mg l^–1 BAP produced an average of 12–32 shoots/ callus culture. The callus retained its potential for shoot regeneration for more than 19 months. The shoots formed an extensive root system and were transferred to pots kept in a greenhouse, where the survival rate was 98%. The plantlets flowered in vitro if transfer to fresh medium or to soil was delayed by 40–50 days. All regenerants were diploid with 2n=30. Received: 13 March 1997 / Revision received: 17 May 1997 / Accepted: 5 July 1997     

Scanning electron microscopical observations on epidermal wound healing in the PlanarianDugesia tigrina

Summary Epidermal wound healing in regeneratingDugesia tigrina (Planaria) has been studied using scanning electron microscopy (SEM). The normal epidermal surface and its differentiations have been descrebed. Observations on living material reveal the highly dynamic state of the wound in invididual animals and its more or less continously changing size due to the state of activity of the animals. These observations show good agreement with the SEM studies, which allow a clear delineation of cellular details of the wound, the wound margins and the apposing epidermal regions. These details are described. The over-all picture of planarian wound healing that emerges is briefly as follows: Epithelization is characterized by absence of proliferation from the old intact epidermis. Variable contraction of smooth muscle cells reduces the wound size to a certain extent. Simultaneously with this and also during a longer period epidermal cells adjacent to the wound are extending and some become highly attenuated. These two processes together are only to a certain degree effective in wound closure because of a definite epidermal cell deficit which is reflected in the emergence of an epidermal wound edge reflecting the maximal contribution of these two processes to an attempt to close the wound. Complete epithelization is effected by the operation of a third mechanism: Recruitment of cell through flow of subjacent blastemal cells (including rhabdite-forming cells) along the wound border; these cells subsequently occupy a peripheral position in the wound. This process is supplemented by cell immigration and insertion into the adjacent old epidermis and in the wound cell sheet. Rhabdite-forming cells contribute predominantly to this process. Eventually integration between old epidermal cells and the newly recruited cells which differentiate into epidermal cells results in final epithelization. Complete wound healing is based on interactions between the epidermal cell system and the regenerating subepidermal membrane-connective tissue filament-muscle cell system.     

AFLP and RAPD analyses of genetic diversity of wild and/or weedy Guizotia (Asteraceae) from Ethiopia

Amplified fragment length polymorphism (AFLP) and random amplified polymorphic DNA (RAPD) markers were used to provide estimates of the comparative genetic variation within and among populations of various Guizotia taxa with the goal of conserving and utilizing their genetic diversity. The percentage of polymorphic loci (P(S)) ranged from 28.5%-90% (AFLP) and 85.6%-99.6% (RAPD). The overall gene diversity estimate () has shown slight variation among taxa ranging from 0.32-0.37 (AFLP) and from 0.22 to 0.28 (RAPD). The within population diversity of "Chelelu" and "Ketcha" was found to be unexpectedly high. Both parameters used to estimate population differentiation (G(ST) and F(ST)) revealed the highest population differentiation G. zavattarii in followed by G. arborescens. Genetic variation among populations within a taxon was highly significant for all the five taxa as revealed by AMOVA (P<0.0001). The need for immediate conservation activities for G. arborescens and G. zavattarii, and factors that contribute to the existing genetic variability and population genetic structures are discussed.     

Phylogenetics and taxonomic delimitation of the genus Guizotia (Asteraceae) based on sequences derived from various chloroplast DNA regions

Parsimony-based phylogenetic analyses of the genus Guizotia were undertaken based on DNA sequence data from the following chloroplast DNA (cpDNA) regions: trnT-trnL, trnL-trnF, trnY-rpoB, trnC-petN, psbM-trnD and rps16-trnQ intergenic spacers, trnL, rps16 and matK-5′trnK introns and matK gene. Out of the 26 primers used in this study, 14 were newly designed. The study was conducted to determine (1) the closest relative of Guizotia abyssinica, (2) the taxonomic status of some Guizotia taxa and (3) the subtribal placement of Guizotia in the tribe Heliantheae. The analyses of the sequence data showed that G. abyssinica, G. scabra ssp. scabra, G. scabra ssp. schimperi and G. villosa are phylogenetically closely related. However, G. scabra ssp. schimperi appeared as the most closely related taxon to G. abyssinica. Based on this phylogenetic analysis, we suggest that the two subspecies of G. scabra are better treated as separate species. The analysis also clearly demonstrated that “Chelelu” and “Ketcha” are distinct Guizotia species. The trnT-trnL and trnL-trnF intergenic spacer-based phylogenetic analysis of various subtribes of the tribe Heliantheae strongly supports the placement of the genus Guizotia within the subtribe Milleriinae.     

Light and electron microscopical immunocytochemical localization of pancreastatin-like immunoreactivity in porcine tissues

Pancreastatin is a 49 amino acid comprising peptide isolated from porcine pancreas that is derived by proteolytic processing from chromogranin A. Using an antibody against the synthetic C-terminal fragment pancreastatin (33-49), we examined the light and electron microscopical immunocytochemical localization of this peptide in porcine tissues. Pancreastatin-like immunoreactivity (PLI) was found in pancreatic somatostatin-, insulin- and glucagon cells in varying intensities; pancreatic polypeptide cells were always negative. At the electron microscopical (EM) level the immunoreactivity was confined to the electron dense core of the secretory granules in the case of somatostatin and insulin cells or to the less electron dense "halo" of the glucagon granules. In the antrum PLI positive cells represented gastrin (G), somatostatin (D) and enterochromaffin (EC) cells, in the duodenum in addition to EC- and G-cells a small number of PLI positive cells showed a positive immunoreaction for glucagon-like peptide (GLP) I and secretin in serial sections. Both norepinephrine and epinephrine containing cells of the adrenal medulla exhibited a strong reaction for PLI. In the pituitary several cell populations stained with varying intensities, including gonadotrophs and thyrotrophys. PLI is present in a distinct and characteristic subpopulation of neuroendocrine cells in various organs. The subcellular localization may indicate a function in the granular concentration, packaging and storage of peptides and amines in the brain-gut endocrine system.     

Light and electron microscopical immunocytochemical localization of pancreastatin-like immunoreactivity in porcine tissues

Summary Pancreastatin is a 49 amino acid comprising peptide isolated from porcine pancreas that is derived by proteolytic processing from chromogranin A. Using an antibody against the synthetic C-terminal fragment pancreastatin (33–49), we examined the light and electron microscopical immunocytochemical localization of this peptide in porcine tissues. Pancreastatin-like immunoreactivity (PLI) was found in pancreatic somatostatin-, insulin- and glucagon cells in varying intensities; pancreatic polypeptide cells were always negative. At the electron microscopical (EM) level the immunoreactivity was confined to the electron dense core of the secretory granules in the case of somatostatin and insulin cells or to the less electron dense halo of the glucagon granules. In the antrum PLI positive cells represented gastrin (G), somatostatin (D) and enterochromaffin (EC) cells, in the duodenum in addition to EC- and G-cells a small number of PLI positive cells showed a positive immunoreaction for glucagon-like peptide (GLP) I and secretin in serial sections. Both norepinephrine and epinephrine containing cells of the adrenal medulla exhibited a strong reaction for PLI. In the pituitary several cell populations stained with varying intensities, including gonadotrophs and thyrotrophs. PLI is present in a distinct and characteristic subpopulation of neuroendocrine cells in various organs. The subcellular localization may indicate a function in the granular concentration, packaging and storage of peptides and amines in the brain-gut endocrine system.