Mucilage Layer Research Articles

The marine lichen Lichina confinis (O. F. Müll.) C. Ag.: ultrastructure and localization of nitrogenase, glutamine synthetase, phycoerythrin and ribulose 1, 5‐bisphosphate carboxylase/oxygenase in the cyanobiont

SUMMARYThallus ultrastructure and the localization of proteins involved in photosynthesis, N2 fixation and ammonia assimilation was studied in the Lichina confinis (O. F. Müll) C. Ag.‐Calothrix symbiosis. The lichen thallus showed profuse branching. Within this, the cyanobiont was located in the cortical zone. Haustoria were frequently observed in contact with vegetative cells of the cyanobiont but not with heterocysts. An extensive mucilage layer containing numerous vesicles occurred around cyanobiont cells. Immunolabelling showed nitrogenase to be exclusively located in heterocysts of the cyanobiont and the free‐living Calothrix sp. Glutamine synthetase (GS) levels in the cyanobiont were found to be drastically decreased compared to the levels in free‐living (cultured) Calothrix sp. Such a decrease was more prominent in mature parts of the thallus than in the apical region. Rubisco was mostly located in carboxysomes of the vegetative cells of the cyanobiont. There were relatively low levels of Rubisco in the cytoplasm of vegetative cells, while heterocysts showed negligible levels. In free‐living (cultured) Calothrix sp., phycoerythrin (PE) was found to be located along the thylakoid membranes both in vegetative cells and heterocysts. Cyanobiont cells showed a similar pattern but the levels were relatively lower.

Taxonomic studies of marine Ascomycotina: ultrastructure of the asci, ascospores, and appendages of Savoryella species

The asci, ascospores, and appendages of Savoryella longispora, Savoryella paucispora, and Savoryella appendiculata were examined at the transmission electron microscope level. Asci of S. longispora and S. appendiculata have a well-developed apical apparatus that consists of a thickened electron-dense ring with a central pore. In S. appendiculata the pore is occluded by a plug of electron-lucent material. The ascus wall comprises an outer narrow electron-opaque layer and an inner electron-lucent layer that are continuous over the apical apparatus. Ascospore walls possess an inner electron-lucent mesosporium and an outer electron-opaque episporium. The episporium of the central cells of all three species is covered with a layer of fibrillar mucilage. Granular strand-like outgrowths of the ascospore wall are present on the polar cells of S. appendiculata and S. paucispora. In all three species the hyaline polar cells of the ascospore contain organelles and in S. appendiculata the polar cells are verrucose. Ascospore appendages are only found in S. appendiculata and these arise endogenously by outgrowth of the endosporium of the polar cell. The differences between the three species are not considered significant at the generic level and therefore all are assigned to the genus Savoryella. Key words: appendages, Ascomycotina, ascospores, marine, taxonomy, ultrastructure.

EFFECT OF NITROGEN STARVATION ON THE BIOCHEMISTRY OF PHORMIDIUM LAMINOSUM (CYANOPHYCEAE)1

ABSTRACTCells of the non‐N2‐fixing cyanobacterium Phormidium laminosum (Agardh) Gomont (strain OH‐1‐pCl1) showed doubling times of 24 h in media containing nitrate and 120 h in media without a nitrogen source. Nitrogen starvation resulted in a drastic decrease in the cellular content of chlorophyll, phycobiliproteins (phycocyanin and allophycocyanin), and other soluble proteins, although the total protein of cells was unchanged. N‐starved cells showed an exocellular layer of mucilage that rapidly increased with starvation time. The appearance of N deficiency symptoms was strongly dependent on culture conditions, and it was faster under the optimal conditions used for cell growth. The relative content of C and N of nitrate‐grown cells remained more or less constant during all growth phases (C/N ratio of ca. 5) but diminished at different rates in N‐starved cells. Cells subjected to N starvation for 48 h had a C/N ratio of more than 10. N starvation also resulted in the selective degradation of soluble poly‐peptides of masses lower than 20 kDa (which include those constituting phycobiliproteins), whereas the relative content of soluble polypeptides of greater size increased.

The application of cryo‐SEM techniques to the study of the symbiotic association in the Azolla leaf cavity

SUMMARYThe preparation of frozen‐hydrated samples for scanning electron microscopy to observe symbionts in Azolla is described and compared to the conventional method of chemical fixation followed by critical‐point drying. The frozen‐hydrated specimens preserve the structure of the associating symbionts and the liquid phase in the Azollaleaf cavity. The leaf cavity structure and the endosymbionts in the frozen‐hydrated specimens were intact and unharmed throughout the fixation. The cyanobiont cells were distributed along the envelope of the leaf cavity, and did not aggregate around the hair cells, as reported for chemical fixation specimens. The mucilage layer removed by the chemical fixation could be observed in the cryo‐fixation specimens, especially at the lower part of the cavity.

Immunogold-cytochemical labelling of ?-glucosidase in the white-rot fungus Coriolus versicolor

Immunogold cytochemical labelling of hyphal sections of Coriolus versicolor showed that β-glucosidase was localised in the extracellular mucilage, cell wall layers and cell interior in hyphae grown on glucose-rich malt extract medium whereas in hyphae grown with carboxymethylcellulose (CMC) as sole carbon source, most labelling was in the cell wall layers and cell interior. Little mucilage was visible around hyphae from these cultures. Hyphae from beechwood cultures showed gold labelling of β-glucosidase in mucilage and fungal cell walls with some intracellular labelling. Biochemical studies of enzyme activity showed that similar amounts of enzyme were detected in the growth medium when cultures were grown on CMC medium, in agitated liquid cultures or in stationary cultures. In agitated cultures grown on glucose-rich malt extract, the activity of β-glucosidase in the medium was 100 times less than that detected in stationary cultures on the same medium. However activity in the hyphae of stationary CMC-grown cultures was similar to that in hyphae from stationary glucose-rich cultures. These data confirm the patterns of gold labelling observed in hyphae from stationary cultures on glucose-rich malt extract when β-glucosidase was immobilised in the extracellular mucilage layer around the hyphae. In this paper we propose that a primary function of the extracellular mucilage produced by hyphae of C. versicolor in vivo is to serve as a matrix for immobilisation of β-glucosidase. Its substrate, cellobiose, which is released as a result of endo-and exoglucanase hydrolysis of cellulose, is absorbed and retained by the gel filtration properties of the mucilage, so encountering the immobilised β-glucosidase. Glucose produced by this reaction is retained within the mucilage matrix around the hyphae before intracellular absorption.

Meiosis, nuclear cyclosis, and auxospore formation inNavicula sensu stricto(Bacillariophyta)

The sexual reproduction of Navicula oblonga is described. Cells aggregate actively and lie side-by-side, touching each other as they enter meiotic prophase. In contrast to some other species traditionally included in Navicula, the gametangia do not subsequently separate and no copulation envelope is produced. Each gametangium forms two gametes, which may or may not become rearranged within the gametangium before its dehiscence. Navicula oblonga is morphologically and behaviourally isogamous. The newly formed auxospores become spherical and secrete a complex tripartite wall, containing a wide central layer of mucilage. This and a thin outer layer separate into two halves as the auxospore begins to expand, remaining as caps over the auxospore apices; a silicified perizonium is produced covering the remainder of the auxospore. Following meiosis, all four haploid nuclei survive in each gametangium, so that the gametes are binucleate; only after plasmogamy do the superfluous nuclei degenerate, the two surviving gametic nuclei fusing to form the diploid zygotic nucleus. The characteristics of reproduction in N. oblonga and other lineolate Navicula species (i.e. Navicula sensu stricto) are listed to provide a basis for future systematic work. During synapsis the chromosomes contract into a synizetic knot, visible in the living cell, which rotates around the interior of the much expanded ellipsoidal nucleus. This is the first report of nuclear cyclosis during diatom meiosis but its presence in dinoflagellates and mammalian spermatocytes suggests that it may be a universal feature of zygotene and early pachytene. Structural heterozygosity seems to be present in some N. oblonga.

Non-nodular endorhizospheric nitrogen fixation in wetland rice

Diazotrophic Alcaligenes faecalis strain A15 isolated from rice roots is associated with rice roots and resides in the mucilage layer. On examination by light and electron microscopy, about 10% of the bacteria that accumulated on the surface entered the root cells. Some bacteria were observed to penetrate the cell wall. By using a 10B α-track technique, the presence of bacteria inside the root was also demonstrated after the rice plants were inoculated with A. faecalis. This was further supported by results of an immunofluorescence study. Both single cells and protoplasts were isolated from rice root and its callus. Transmission and scanning electron microscopy showed that A. faecalis grew inside the root cell. Callus, developed from rice root cells inoculated with this bacterium, grew well in nitrogen-free culture medium, while it died within 30 days without inoculation. Nitrogen fixation in the callus was confirmed by 15N tracer methodology and the rate ranged from 18.5 to 35.5 μg N fixed/g dry weight callus per day.Key words: Alcaligenes faecalis, endorhizospheric nitrogen fixation, rice–bacteria symbiont.

The effects of immobilization on the biochemical, physiological and morphological features of Anabaena azollae

Anabaena azollae, a presumptive isolate from Azolla filiculoides, was immobilized in polyurethane foam, hydrophilic polyvinyl foam and alginate. When viewed by low-temperature scanning electron microscopy a thick mucilage layer covered the surface of both cells and matrix; this closely resembles the mode of attachment of the symbiont Anabaena in the Azolla leaf cavity. The heterocyst frequency of the immobilized A. azollae doubled relative to free-living cells and reached a level of 14-17%. Immobilization induced increases in both hydrogen production via nitrogenase or hydrogenase and in the rates and stabilization of acetylene reduction (N2-fixation). Ammonia production by immobilized cells with L-methionine-D,L-sulfoximine (MSX) is greater than that of freeliving cells. Immobilized cells without MSX were, however, able to excrete ammonium at lower rates thus emulating the characteristic of the symbiotic cyanobacteria (A. azollae) in the leaf cavity of Azolla.

Early infection events in the nodulation of the non-legume Parasponia andersonii by Bradyrhizobium

The non-legume Parasponia andersonii was found to have an infection zone close behind the growing tip of the tap root which is similar to that found in legume infections by Bradyrhizobium. An examination of spot inoculated sites in the infection zone showed that bacteria had colonized the root surface and begun to erode the mucilage layer of the primary cell wall of epidermal cells within 24 h of inoculation. Four days after inoculation swelling of the root beneath the area of surface erosion was visible and was followed by the rupturing of the overlying epidermal layer and the emergence of a mass of dividing cells by 6 days. The removal of the epidermis and the emergence of exposed cells provided a site through which bacteria could enter the root and colonize the cortex. The initial infection events of root hair curling and the formation of infection threads within root hairs found in legume and other non-legume associations were not observed in the invasion of P. andersonii. P. andersonii infection requires the initiation of cell division to form a ‘wound’ for intercellular invasion followed by the formation of infection threads from colonies within the root cortex.

Gypsum and halite associated with the cyanobacteriumEntophysalis

Abstract A study has been made on stalactite‐like structures formed by the cyanobacterium (blue‐green alga) En‐tophysalis major, growing on the roof of an undercut cliff facing the lagoon of Aldabra Atoll. The cyanobacterial cells grow in a rubbery, brown, gelatinous mucilage that contains some crystals; this mucilage surrounds a central region filled partly with gas and partly with further crystals. Halite is the predominant mineral in the mucilage, and gypsum the only mineral in the inner region. There is no evidence for a direct causal relationship between cyanobacterial metabolism and mineral crystallization, but the organic mucilage may have exerted an indirect physical control. A theory is suggested to explain the deposition of gypsum and halite, which depends on loss of water from the surface of the mucilage layer, and the layer as a whole acting as a semipermeable membrane. As the water volume decreases, gypsum will be deposited first, but subsequently, with increasing evaporation, there will be a mixture of gypsum and halite and finally halite only.

Cytological and histochemical characteristics of the axenic root surface of Alnus glutinosa

The aim of the present study was to investigate the Alnus root surface using seedlings grown axenically. This study has focused on root zones where infection by the symbiotic actinomycete Frankia takes place. The zones examined extend from the root cap to the emerging root hair zone. The root cap ensheaths the Alnus root apex and extends over the root surface as a layer of highly flattened cells closely appressed to the root epidermal cell wall. These cells contain phenolic compounds as demonstrated by various histochemical tests. They are externally bordered by a thin cell wall coated by a thin mucilage layer. The root cap is ruptured when underlying epidermal cells elongate, and cell remnants are still found in the emerging root hair zone. Young emerging root hairs are bordered externally by a cell wall covered by a thin mucilage layer which reacts positively to the tests used for the detection of polysaccharides, glycoproteins, and anionic sites. The characteristics of the Alnus root surface and the biological function of mucilage and phenols present at the root surface are discussed in relation to the infection process.

Ultrastructural study of the maize epidermal root surface. I. Preservation and extent of the mucilage layer

This study clarifies the relationships between the root mucilage and the epidermal cell-wall in axenically grown maize roots. Mucilage appears to overlay the epidermal cell-wall which has two distinct layers. This mucilage is well preserved after cationized ferritin fixation and PATAg staining. It extends all over the entire root epidermis.

ULTRASTRUCTURE OF GERMINATING CARPOSPORES OFPORPHYRA VARIEGATA(KJELLM.) HUS (BANGIALES, RHODOPHYTA)1

ABSTRACTThe fine structure of released, attached, and germinating carpospores ofPorphyra variegata(Kjellm.) Hus is described. Adhesive vesicles, formed during sporogenesis and discharged upon settling of the spore, produced a layer of adhesive mucilage around the spore and filled a deep imagination on the spore's ventral side. The mucilage layer was punctured by the emergence of a germ tube. Both spore and germ tube were lined by newly deposited cell wall. Germination was accompanied by vacuolation and starch mobilization. The morphological development of the sporeling was not noticeably influenced by the great variability of the timing, location, and orientation of septum formation. The attached carpospore possessed a plastid like that of gametophyte cells: stellate with one large central pyrenoid and no peripheral encircling thylakoids. Cells of mature vegetative cells of the conchocelis had plastids that were elongate and parietal and had multiple pyrenoids and encircling thylakoids. Most stages in the transition between the two forms of plastids occurred during carpospore germination.

Induction of dormancy during seed development by endogenous abscisic acid: studies on abscisic acid deficient genotypes of Arabidopsis thaliana (L.) Heynh.

Mutant lines of Arabidopsis thaliana (L.) Heynh., which are characterized by symptoms of withering and the absence of seed dormancy, showed much lower levels of endogenous abscisic acid (ABA) in developing seeds and fruits (siliquae) than the wild type. Reciprocal crosses of wild type and ABA-deficient mutants showed a dual origin of ABA in developing seeds. The genotype of the mother plant regulated a sharp rise in ABA content half-way seed development (maternal ABA). The genotype of the embryo and endosperm was responsible for a second ABA fraction (embryonic ABA), which reached much lower levels, but persisted for some time after the maximum in maternal ABA. The onset of dormancy correlated well with the presence of the embryonic ABA fraction and not with the maternal ABA. Dormancy developed in both the absence and presence of maternal ABA in the seeds. In this respect maternal ABA resembled exogenously applied ABA which did not induce dormancy in ABA-deficient seeds. However, both maternal and applied ABA stimulated the formation of a mucilage layer around the testa, which could be observed during imbibition of the mature seeds. In the mature state, ABA-deficient seeds germinated in the siliquae on the plant, but only when the atmosphere surrounding the plant was kept at high relative humidity. In younger stages germination in siliquae occurred after isolation from the plants and incubation on wet filter paper. Therefore, it seems that limited access to water is the primary trigger for the developmental arrest in these seeds.

Bioconcentration of a Hexachlorobiphenyl in Great Lakes Planktonic Algae

The bioconcentration of 2,4,5,2′,4′,5′-hexachlorobiphenyl (HCB) was examined in the Great Lakes algae Fragilaria crotonensis, Ankistrodesmus falcatus, and Microcystis sp. The bioconcentration factors varied from species to species, whether they were expressed in terms of cell number, dry weight, cellular carbon, or cellular lipid. The factors were in the range of 105–106 and increased with decreasing biomass. The existence of a mucilage layer in F. crotonensis was associated with a twofold increase in the bioconcentration factor. Surface adsorption appeared to contribute only slightly to the bioaccumulation of HCB. HCB desorbed from all species but at a much slower rate than its adsorption.Key words: bioconcentration, bioaccumulation, polychlorinated biphenyls, hexachlorobiphenyl, adsorption, desorption, algae

ELECTRON MICROBEAM ANALYSIS AND SCANNING ELECTRON MICROSCOPY OF SOIL-ROOT INTERFACES

ABSTRACT We conducted quantitative point count determinations of phosphorus, potassium, calcium, and magnesium by electron microbeam analysis and scanning electron microscopy of soil-root interfaces with soil-root samples from 30-day-old peanut and soybean plants, grown in Davidson and Cecil soil. Scanning electron micrographs showed undistorted cellular details of the plant roots embedded in the soil mass. Electron microbeam counts revealed that the soil contained lower concentrations of P, K, and Ca than the root tissue. The Mg concentration showed a tendency to be higher in the soil than in the roots. An ascending ion concentration gradient was noticed in the soil from 0.40 to 0.10 mm from the root surface. Nevertheless, a slight decrease in ion concentration was observed 0.05 mm from the root, which was attributed to the presence of a mucilage layer bridging the soil with the root surface. On the basis of a sharp break in element distribution with distance to the root, we estimated the soil rhizosphere to be 0.20 mm thick. Keeping this thin layer of soil saturated was thought to be more beneficial than keeping the bulk of soil saturated with nutrients. Specific accumulation zones of K and Ca were noted in root tissue. Highest concentrations of K and Ca were measured in cortex and epidermis, respectively. Lower levels of K, Ca, and Mg were detected in soybean than in peanut roots, indicating different nutrient requirements between plant species. The results of element counts by electron microbeam analysis in peanut and soybean roots were within ranges of concentrations measured by conventional methods with dry-ashing and atomic absorption spectrophotometry.

Origin of Ooids in Pleistocene Miami Limestone, Florida Keys: ABSTRACT

Scanning electron microscopy reveals that ooids in this marine unit are of biogenic origin in the sense that endolithic and epilithic algae, fungi?, and mucilage played primary roles in constructing laminae in the cortex of each ooid. Three end-member types of original laminae are recognized (1, 2, 3, below); each is made up of fundamental building blocks of aragonite crystals typically shaped like miniature batons. (1) Filaform (common): laminae composed of a network of calcified algal or possibly fungal filaments, or both. Batons in such laminae are typically less than 1 µ long and most are randomly oriented relative to the nucleus. The batons formed within a mucilaginous sheath surrounding the original algae or fungi. Filaments in such laminae could go through lif as epiliths or begin as epiliths that became endoliths which eventually became epiliths once again. (2) Spheroform (rare): laminae composed mainly of calcified spherical bodies of algal or fungal origin. (3) Sheet (common): pavement-like layers of batons that are typically 0.5 to 2.0 µ long and are oriented tangentially relative to the nucleus. Most batons in type (3) laminae originated in a layer of mucilage or mucous that did not surround algae or fungi, but which enveloped all or much of the surface of a developing ooid. Examples of typical sequences of laminae development are (1)-(1)-(1) etc, (3)-(3)-(3) etc, and (1)-(3)-(1)-(3) etc, possibly with a final type (2) lamina. Contrary to evidence from many modern marine aragonite ooids, filamentous algae was not a constructive fact r in the formation of all laminae in the cortex of all ooids in the Miami Limestone. End_of_Article - Last_Page 943------------

A histological and histochemical comparison of the mucilages on the root tips of several grasses

Young, axenically grown roots of grasses are covered by two types of mucilage. Gelatinous material originates from the root cap, and a firm, uniformly thick mucilage overlies the columnar epidermal cells. Histochemical properties of these mucilages are similar in corn, wheat, barley, oats, sorghum, and a Sudan grass – sorghum hybrid.The epidermal mucilage has a thin outer and a thicker inner layer distinct from the epidermal cell wall. Both mucilage layers are strongly autofluorescent, birefringent, and PAS positive. Reactions of the outer layer and cell wall indicate carboxyl groups. These are absent from the inner mucilage. Root cap mucilage has a inner region with histochemical properties resembling those of the inner epidermal mucilage. The outer portion of the root cap mucilage is not fluorescent, not birefringent, weakly PAS positive, and carboxylated.

SEED DORMANCY AS EXPLAINED BY THE ANATOMY OF EMBRYO ENVELOPES

ABSTRACT The effects of embryo envelopes dealt with here are: impermeability to water, impermeability to oxygen, and mechanical resistance to radicle protrusion. To prevent water penetration, one or more layers of the embryo envelopes, as well as all possible openings in it such as the hilum or chalaza of the seed coat, should be watertight. This layer usually consists of compactly arranged cells, with various hydrophobic compounds impregnated into the cellulose network of the walls and/or deposited upon them. Restriction of oxygen without hindrance of water penetration may be due to a long path through which the dissolved oxygen has to diffuse in water, to a continuous layer of mucilage covering the embryo, to oxygen-consuming compounds in the envelopes, and to selective permeability of living cells. Resistance to radicle penetration is caused by any type of mechanical tissue that has a higher mechanical restraining force than the growth potential of the embryo.

The fine structure of fertilization in the fern Marsilea vestita.

The ultrastructural details of fertilization in the fern Marsilea vestita, including gamete approach and fusion, the fate of the spermatozoid organelles and the development of a possible block to polyspermy are described. The spermatozoid approaches the egg through layers of mucilage that surround the megaspores. It moves down the neck of the archegonium into the cavity above the egg. In order to reach the egg, it must move through a small hole in the thick wall that lies across the top of the egg. The fusion of the plasma membranes of the gametes results in an outflow of egg cytoplasm into the clear space under the sperm plasma membrane, creating a fertilization cone. All the organelles of the fertilizing spermatozoid, including nucleus, mitochondrion, microtubule ribbon, multilayered structure, and flagellar band, with approximately 150 flagella, enter the egg cytoplasm. The nucleus enters as a condensed rod of chromatin with no nuclear envelope. The chromatin begins to disperse immediately and a new nuclear envelope is formed around the chromatin by egg endoplasmic reticulum. The mitochondrion and the microtubules of the ribbon and flagella are broken down, but the fates of the flagellar band and the multilayered structure have not been determined. After spermatozoid penetration, a new extracellular layer appears above the surface of the egg, beginning in the region of sperm penetration and spreading across the top of the egg. This layer may be important in preventing other spermatozoids from fusing with the egg.