DEVELOPMENT OF MUCILAGINOUS SURFACES IN EUGLENOIDS. II. FLAGELLATED,CREEPING AND PALMELLOID CELLS OF EUGLENA1

Critical-point dried (CPD) cells from clonal cultures of Euglena gracilis Klebs (Z strain), E. deses Ehrb., E. tripteris (Duj.) Klebs and E. myxocylindracea Bold & MacEntee were examined by scanning electron microscopy. Flagellated motile cells of E. gracilis are naked except for a few strands of mucilage on the posterior tip. Flagellated cells of E. tripteris have a permanent mucilage coating often of uneven distribution and usually not as well developed as that of nonflagellated creeping cells which have a distinctive mucilage. In E. deses the coating appears rough due to the aggregation of isolated groups of strands above the cell surface. In E. tripteris the coating appears smooth except for breaks near the articulation of the pellicular strips where the mucilage may rise above the surface to form waves. At high magnification this mucilage consists of a network of strands generally lying parallel to the cell surface; the strands become obscure in some specimens. In E. myxocylindracea elongated, mucilage-coated cells contract to form spheres which undergo further mucilage deposition producing the mucilage covering of palmellae. As palmellae mature, the mucilage surface becomes less porous and the individuality of most mucilage strands is lost.     

WILD GAMETOPHYTES OF PHANEROSORUS MAJOR (MATONIACEAE)

The gametophytes of Phanerosorus major collected from wild populations in Seram Island are described. Young gametophytes are slender, ribbon-like and uniformly one cell thick. They develop to old gametophytes with a broad thick cushion and coarsely ruffled wings. The gametophytes are monoecious and protandrous, although archegonia-bearing thalli occasionally become antheridia-bearing. Massive antheridia form on the ventral surface of young and old gametophytes while archegonia are borne on the cushion of old ones. Both young and old gametophytes reproduce vegetatively. The gametophytic characters are compared with those of Matonia. The life cycle of P. major is discussed with reference to its ecology.     

The role of COBRA‐LIKE 2 function,as part of the complex network of interacting pathways regulating Arabidopsis seed mucilage polysaccharide matrix organization

The production of hydrophilic mucilage along the course of seed coat epidermal cell differentiation is a common adaptation in angiosperms. Previous studies have identified COBRA‐LIKE 2 (COBL2), a member of the COBRA‐LIKE gene family, as a novel component required for crystalline cellulose deposition in seed coat epidermal cells. In recent years, Arabidopsis seed coat epidermal cells (SCEs), also called mucilage secretory cells, have emerged as a powerful model system for the study of plant cell wall components biosynthesis, secretion, assembly and de muro modification. Despite accumulating data, the molecular mechanism of COBL function remains largely unknown. In the current research, we utilized genetic interactions to study the role of COBL2 as part of the protein network required for seed mucilage production. Using correlative phenotyping of structural and biochemical characteristics, unique features of the cobl2 extruded mucilage are revealed, including: ‘unraveled’ ray morphology, loss of primary cell wall ‘pyramidal’ organization, reduced Ruthenium red staining intensity of the adherent mucilage layer, and increased levels of the monosaccharides arabinose and galactose. Examination of the cobl2cesa5 double mutant provides insight into the interface between COBL function and cellulose deposition. Additionally, genetic interactions between cobl2 and fei1fei2 as well as between each of these mutants to mucilage‐modified 2 (mum2) suggest that COBL2 functions independently of the FEI‐SOS pathway. Altogether, the presented data place COBL2 within the complex protein network required for cell wall deposition in the context of seed mucilage and introduce new methodology expending the seed mucilage phenotyping toolbox.     

ACTIVE GLIDING MOTILITY IN AN ARAPHID MARINE DIATOM,ARDISSONEA (FORMERLY SYNEDRA) CRYSTALLINA1

Active gliding movement over long distances was observed and filmed in the marine pennate diatom Ardissonea (Synedra) crystallina (Agardh) Kütz. Typical speeds measured ca. 1–2 μm-s^?1. Motion wax often smooth and steady; however, discontinuous jerky motions and rolling movements were common. Motion, was associated with secretion of twin or, less commonly, single straight trails of mucilage from one end of the cell. In a few instances, reversal in direction was related to cessation of mucilage secretion at one end and commencement at the other. Temporary cessation of movement due to an obstruction was accompanied by a build-up of mucilage at one end of the cell. Mucilage was apparently secreted at two specific sites at each end of the cell and was stained by alcian blue. Persistent trails were visible under scanning electron microscopy (SEM). SEM confirmed that cells had no raphes or labiate processes. The apparent site of secretion was a deep groove formed at the junction of the valve and valvocopula (first girdle band) at each end of the cell. Transmission electron microscopy confirmed the presence of mucilage vesicles in the cytoplasm, but these were not in any manner obviously related to secretion nor was any morphological structure associated with secretion. Cells often become epiphytic through secretion of a terminal stipe. Both stipe secretion and movement may involve the same structural differentiation of the frustule. These results demonstrate a previously unrecorded type of diatom motility. The mechanism, involves mucilage secretion and appears similar to that seen, for example, in some other algae such as the desmids (green algae).     

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.     

CELLULAR VOLUME AND TISSUE PARTITIONING IN CAPS OF PRIMARY ROOTS OF ZEA MAYS

Cellular and tissue volumes were measured in caps of primary roots of Zea mays. There is an 850% increase in cellular volume as cellular function changes from that of being meristematic (i.e., calyptrogen cells) to graviperception (i.e., columella cells), and a 22% increase in cellular volume during the functional transition from graviperception to the production and secretion of mucilage. Cellular volume does not change significantly after cells cease mucilage production and are sloughed from the cap. Root caps of Z. mays allocate 7.5% of their volume for regeneration, 14.9% for graviperception, 24.3% for the transition of function from graviperception to mucilage production and secretion, and 38.7% for the production and secretion of mucilage. The remaining 14.5% of the cap volume is comprised of cells being sloughed from the cap.     

Ethylene is a modulator of gibberellic acid-induced antheridiogenesis in <Emphasis Type="Italic">Anemia phyllitidis</Emphasis> gametophytes

In fern (Anemia phyllitidis) gametophytes cellulose in the walls of the antheridial zone cells which was organized in clusters and spots was transformed via dispersed form to fibrillar arrangement (layered in oblique and perpendicular array in relation to the transverse direction of cell expansion) during antheridiogenesis induced by gibberellic acid (GA₃) and/or enhanced by 1-aminocyclopropane-1-carboxylic acid (ACC). In the ACC-treated gametophytes, where antheridia were not induced, the cellulose was arranged in the same manner. Aminooxyacetic acid (AOA), which inhibits antheridiogenesis and development of fern gametophytes, produced in the cell walls both random and longitudinal type of organization of cellulose microfibrils, however, in the GA₃/AOA-treated plants the oblique type was also observed. The total numbers of cells with perpendicular and/or oblique type of cellulose microfibrils in the GA₃-, GA₃/ACC-and GA₃/AOA-treated gametophytes corresponded to the average number of antheridia formed. Moreover, it was found that the extracts from the gametophytes treated with GA₃ or with the mixture of GA₃ and ACC contained significantly less soluble sugars but more α-amylase-and endoglucanase-released sugars than the extracts from the gametophytes of the other series. Thin layer chromatography of the samples from the cell wall extracts hydrolyzed by endoglucanase contained xylose and cellobiose which suggested that these sugars built the xyloglucans, hemicellulose polymers responsible for tethering of walls of fern gametophyte cells like in higher plants.     

HAPLOID PARTHENOGENETIC SPOROPHYTES OF LAMINARIA JAPONICA (PHAEOPHYCEAE)1

Parthenogenetic sporophytes were obtained from three strains of Laminaria japonica Areschoug. These sporophytes grew to maturity in the sea, producine spores that all grew into female gametophytes. These female gametophytes gave rise to another generation of parthenogenetic sporophytes during the next year, so that by the year 1990 parthenogenetic sporophytes had been cultivated for 12, 9, and 7 generations, respectively, for the three strains. When female gametophytes from parthenogenetic sporophytes were combined with normal male gametophytes, normal sporophytes that reproduced and gave rise to both female and male gametophytes were obtained. The parthenogenetic sporophytes were shorter and narrower than the normal sporophytes of the same strain. Chromosome counts on mature sporophytes showed that normal sporophytes (from fertilized eggs) were diploid (2n = approximately 40) and that the spores they produced were haploid (n = approximately 20), while nuclei from both somatic and sporangial cells in parthenogenetic sporophytes were haploid. All gametophytes were haploid. Young sporophytes derived from cultures with both female and male gametophytes were diploid, while young, sporophytes obtained from female gametophytes from parthenogenetic sporophytes had haploid, diploid, or polyploidy chromosome numbers. Polyploidy was associated with abnormal cell shapes. The presence of haploid parthenogenetic sporophytes should be use in breeding kelp strains with useful characteristics, since the sporophyte phenotype is expressed from a haploid genotype which can be more readily selected.     

Comparative development of heavily asymmetric-cordate gametophytes of <Emphasis Type="Italic">Anemia phyllitidis</Emphasis> (Anemiaceae) focusing on meristem behavior

Development of heavily asymmetric cordate gametophytes of Anemia phyllitidis (Anemiaceae), one of the schizaeoid ferns, was examined using a sequential observation technique; epi-illuminated light micrographs of the same growing gametophytes were taken approximately every 24 h. The apical cell-like wedge-shaped cell was produced once from the terminal cell of a germ filament, but it stopped dividing soon after production of one or two derivative cells. Without a functional apical cell, the gametophyte developed by intercalary growth until the early stage of wing formation, and then the multicellular (pluricellular) meristem arose from the lower lateral side of the gametophyte. This was in sharp contrast to the observation that the multicellular meristem forms in place of the apical cell in typical cordate gametophytes. Loss of the functional apical cell probably caused a site-shift in the multicellular meristem of the Anemia phyllitidis gametophyte during evolution from apical to lateral. The results suggest that apical cell-based and multicellular meristems are primarily independent of each other. The multicellular meristem produced cells equally in the distal and proximal directions to form wings in both directions but proximally produced cells divided much less frequently. As a result, a heavily asymmetric gametophyte was formed.     

GAMETOPHYTES AND YOUNG SPOROPHYTES OF OPHIOGLOSSUM CROTALOPHOROIDES WALT.

The lens-shaped, dorsiventral gametophytes of Ophioglossum crotalophoroides are superficially different from the cylindrical gametophytes of other species of Ophioglossum. However, they have the same features as other Ophioglossum gametophytes (fundamentally axial organization, radially symmetrical apical meristem, radial distribution of gametangia) except that the cylindrical axis is reduced in length. Young sporophyte development is unique in the genus: all primary organs clearly arise from the embryo and develop simultaneously. The length of the life cycle of O. crotalophoroicles is considerably shorter than that of some other species in the Ophioglossaceae. A timetable for gametophyte and young sporophyte development is postulated. Spores germinate soon after they are released in the spring, and mature gametophytes develop by the next growing season. Fertilization occurs approximately one year after spore dispersal, and after two years, the photosynthetic first leaf of the young sporophyte emerges.     

GROWTH PATTERNS AND MOTILITY OF SPIROGYRA SP. AND CLOSTERIUM ACEROSUM1,2

Spirogyra and Closterium exhibit active motility. This motility is associated with the secretion of pectic mucilage from the cells. The gliding of these cells is not directed toward light but photosynthesis is the energy source for it. The secretion of mucilage causes older Closterium cultures to become thick gelatinous clusters. Spirogyra filaments when undisturbed grow to form thick multistranded rings. This growth pattern might result from the tendency of the filaments to rotate on their long axis.     

Fucose in the surface deposits of axenic and field grown roots ofZea mays L.

Summary The location of materials containing terminal fucose residues on the surface of axenic and field grown roots of corn has been determined.Binding patterns of FITC-labelled,Lotus purpureus Moench lectin indicate the presence of the fucose residues in the cell walls and mucilage of the peripheral region of the root cap. During development, fucose residues also appear in the outer periclinal walls and overlying mucilage of columnar epidermal cells. Surface material rich in these residues persists between the mature root hairs but is not found on their surface. Fucose-rich mucilage is present on the exposed surface of aerial roots and at the point where they enter the soil. No lectin binding residues are indicated elsewhere in the roots.     

ULTRASTRUCTURE OF TETRASPOROGENESIS IN PALMARIA PALMATA (RHODOPHYTA)1

The tetrasporangial initial in Palmaria palmata (L.) O. Kuntze (formerly Rhodymenia palmata (L.) Greville) arises from a cortex cell which enlarges and deposits a protein-rich wall layer. This cell undergoes mitosis to form a tetrasporocyte and a stalk cell. Synaptonemal complexes are formed in the sporocyte nucleus while in the cytoplasm floridean starch is deposited in association with ER or with particles presumed to be ribosomes. Microbody-like structures become numerous between the nuclear envelope and perinuclear ER, and clusters of non-membranous, spherical structures also are associated with the nucleus. Chromatin condensation is reversed following pachytene and a prolonged diffuse stage ensues, when dictyosomes and ER produce vesicles which deposit mucilage rich in sulfated and acidic polysaccharides around the tetrasporocyte. A conspicuous lenticular thickening of the mucilage sheath develops at the apical end of the sporangium. Dictyosomes are frequently associated with mitochondria which may be associated with chloroplasts. Following nuclear divisions the tetrasporocyte is cleaved into four spores by sequentially initiated, but simultaneously completed periclinal and anticlinal furrows. When mucilage deposition ceases, the dictyosomes begin to produce vesicles with glycoprotein-rich contents. These vesicles are abundant in released tetraspores, and they probably contain adhesive material aiding in the attachment of the liberated spores.     

Mucilage secretion: an adaptive mechanism to reduce seed removal by soil erosion?

Diaspores of many plant species inhabiting open vegetation in semi‐arid environments secrete mucilage after wetting (myxospermy) that glues the diaspores to the ground and prevents movement when the mucilage dries. In the present study, we test whether mucilage secretion can be considered as a selective response to soil erosion in plant species inhabiting semi‐arid environments. We relate the amount and type of mucilage secretion by seeds of Helianthemum violaceum and Fumana ericifolia (Cistaceae) to the number of raindrop impacts needed to remove these seeds after gluing them with their own mucilage to the ground and also the time that these seeds resist water run‐off without detaching. We also compare the amount of seed mucilage production by plants growing in habitats without erosion and plants affected by severe erosion by fitting mixed effect models. Our results show an important phenotypic variation in the amount of mucilage secretion in both species, although it is suggested that the effect of mucilage secretion in the rate of seed removal by erosion is species‐ and mechanism‐dependent. For F. ericifolia, the amount of mucilage secreted by the seeds is directly proportional to their resistance to raindrop impacts and is positively related to the intensity of the erosive processes that the plants experience. Nevertheless, all the seeds resist the force of run‐off during 60 min, irrespective of the amount of mucilage they produce. In H. violaceum, mucilage secretion per se, and not the amount of mucilage produced by the seeds, has an effect on the rate of seed removal by erosive processes. Furthermore, cellulosic fibrils were found only in the mucilage of F. ericifolia but not in H. violaceum. Overall, our results only partially support the hypothesis that a selective response to soil erosion exists. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 241–251.     

Mucilage secretion and the movements of blue-green algae

Summary Recent discoveries of ultrastructures which might be involved in the gliding movements of blue-green algae have been reviewed, and in the light of these discoveries the role of mucilage secretion in movement has been reconsidered. The formation and behaviour of mucilage rings in filaments ofAnabaena cylindrica is described. The behaviour of the mucilage rings indicates that each cell has an autonomous gliding mechanism which is capable of immediate reversal, and that the gliding mechanism is probably located over the whole surface, rather than at the ends, of the cells. It follows that if mucilage secretion is the cause of movement it must take place over the whole surface of the cell: but if the ends of the cell are the sites of mucilage secretion, as seems likely, then gliding movement must be performed by some other process.A rather remarkable clumping phenomenon is described which takes place in dense suspensions ofAnabaena. It results from the gliding movements of randomly orientated filaments made mutually adhesive by the mucilage which surrounds them.     

OBSERVATIONS ON THE LIFE HISTORY OF PAPENFUSSIELLA CALLITRICHA (PHAEOPHYCEAE,CHORDARIALES) IN CULTURE1

Papenfussiella callitricha (Rosenv.) Kylin from eastern Canada was studied in culture. Zoids from unilocular sporangia develop into microscopic, filamentous, dioecious gametophytes which produce isogametes in filament cells and few-chambered plurilocular gametangia. Unfused gametes germinate to reproduce the gametophytes. Fusion takes place between a settled (“female”) and a motile (“male”) gamete. The zygote gives rise to a filamentous plethysmothallus that reproduces asexually by zoids formed in thallus cells and in few-chambered plurilocular zoidangia. Erect macrothalli are produced on the plethysmothallus, beginning with the formation of upright filaments. Later on, these filaments become the terminal assimilators of the macrothalli. Further assimilatory filaments, rhizoids, and unilocular sporangia are produced in a branching region at the base of the terminal assimilator. Zoids from unilocular sporangia formed in culture germinate to reestablish the gametophyte phase. Chromosome counts yielded n = 19 ± 3 for the gametophytes, and 32 ± 6 for the sporophyte, both plethysmothallus and macrothallus.     

ULTRASTRUCTURE OF CARPOSPOROPHYTE DEVELOPMENT IN THE RED ALGA GLOIOSIPHONIA VERTICILLARIS (CRYPTONEMIALES,GLOIOSIPHONIACEAE)

The ultrastructure of carposporophyte development is described for the red alga Gloiosiphonia verticillaris Farl. The auxiliary cell produces gonimoblast initials, which divide to produce two types of gonimoblast cells—the nondividing vacuolate cells and terminal generative gonimoblast cells. The generative gonimoblast cells form clusters of carpospore initials, which eventually differentiate into carpospores. After gonimoblast filaments are formed, the auxiliary cell undergoes autolysis, causing degeneration of septal plugs between the auxiliary cell and adjacent cells, thus forming a fusion cell. Since this cell lacks starch and appears degenerate throughout carposporophyte development, a nutritive function cannot be ascribed to the fusion cell. Carpospore differentiation is simple and proceeds through three developmental stages. Young carpospores structurally resemble gonimoblast cells, because they contain undeveloped plastids, large quantities of floridean starch, and are surrounded by extensive mucilage instead of a distinct wall. In addition, dictyosomes form and begin to produce vesicles with fibrous contents representing carpospore wall material. During the intermediate stage, dictyosomes continue to produce vesicles that contribute additional carpospore wall material, thereby compressing the mucilage and creating a darker-staining layer outside the carpospore wall. Plastids form internal thylakoids by invaginations of the inner membrane of the peripheral thylakoid. The endoplasmic reticulum forms large granular vacuoles that appear to be degraded during subsequent stages of development. Mature carpospores form cored vesicles. They also contain mature chloroplasts, large amounts of floridean starch, and occasionally granular vacuoles. During this stage, interconnecting carpospore-carpospore and carpospore-gonimoblast cell septal plugs begin to undergo degeneration. This process may be mediated by tubular structures.     

ROLE OF GOLGI APPARATUS IN MUCILAGE PRODUCTION AND CYST FORMATION IN EUGLENA GRACILIS (EUGLENOPHYCEAE)1

Dark grown cells of Euglena gracilis Klebs (strain Z Pringsheim) encyst when placed in minus nitrogen media for 48–72 h in the dark. The number of cisternae per dictyosome decreases from 10–20 to 6–12 during encystment. Cisternae dilate and fill with mucilage within 12–18 h after induction. The material is secreted into the reservoir and deposited onto the cell surface. The encysting cells rotate as they develop resulting in the deposition of a thick mucilaginous layer over the cell surface. The secretion product has been identified as polysaccharide with the periodic acid-silver methenamine reaction. Mucilage has not been observed in the endoplasmic reticulum adjacent to the pellicle. The product present in the dictyosornes and on the cell surface react identically to the silver reagent.     

THE COMPLEX POLYSACCHARIDES OF THE RAPHID DIATOM PINNULARIA VIRIDIS (BACILLARIOPHYCEAE)1

A combination of carbohydrate analysis and atomic force microscopy (AFM) was used to characterize the polysaccharides of the pennate diatom, Pinnularia viridis (Nitzsch) Ehrenberg. Polymeric substances were fractionated into those in the spent culture medium (SCM) and those sequentially extracted from the cells with water at 45° C (WW), NaHCO₃ containing EDTA at 95° C (HB), and 1 M NaOH containing NaBH₄ at 95° C. Carbohydrate, protein, and sulfate were detected in all the fractions, but their relative proportions differed significantly. Nineteen sugars were identified, including pentoses, hexoses, 6‐deoxyhexoses, O‐methylated sugars, aminohexoses, and traces of uronic acids. To some extent, the same constituent monosaccharides and a proportion of the linkage patterns occurred in all four fractions, indicating the fractions contained a spectrum of highly heterogeneous but structurally related polysaccharides. Several carbohydrates were enriched in specific fractions. A soluble, partially substituted, 3‐linked galactan was slightly enriched in the SCM. The WW fraction was highly enriched in 3‐linked glucan, presumably derived from chrysolaminaran. Chemical and AFM data for the WW and HB fractions indicated that compositional differences were associated with substantial changes in the morphology and properties of the cell surface mucilage. Soluble polymers relatively enriched in fucose conferred a degree of softness and compressibility to the mucilage, whereas most of the mucilage comprised firmer more gelatinous polymers comparatively enriched in rhamnose. The frustule residue dissolved during extraction with NaOH, and a partially substituted 3‐linked mannan, together with relatively large amounts of protein, was obtained.     

Some features of secretory systems in plants

Synopsis Recent work on secretion in plants is reviewed, with emphasis on the anatomy and physiology of root cap cells in higher plants, the stalked glands ofDrosera capensis, and the secretory mechanism ofDionaea muscipula. Cells of the root cap of higher plants switch from a geo-perceptive role to one of mucilage secretion at maturation. Features of this process, the role of the Golgi and the pathway for mucilage distribution are reviewed. In contrast, the stalked glands of the leaves ofDrosera capensis are much longer lived and have a complex anatomy. The mechanisms for mucilage secretion, protein absorption and the role of the cell membranes in the internal secretion of the protein are described, using data from X-ray microscopv. The secretion of fluid and protein byDionaea is stimulated by various nitrogen-containing compounds. Uric acid, often excreted by captured insects, is particularly effective in this respect.