Insights into a hydration regulating system in Cupressus pollen grains

Background and Aims

Hydration, rupture and exine opening due to the sudden and large expansion of intine are typical of taxoid-type pollen grains. A hemispheric outgrowth external to the exine was observed on Cupressus and Juniperus pollen grains before the intine swelling and exine release. However, the actual existence of this permanent or temporary structure and its precise role in pollen hydration is still being debated. The aim of this paper is to collect information on the actual presence of this peculiar outgrowth on the surface of the Cupressus pollen grain, its structure, composition and function.

Methods

Pollen grains of several Cupressus species were observed using various techniques and methodologies, under light and fluorescence microscopy, phase-contrast microscopy, confocal microscopy, scanning electron microscopy, and an environmental scanning electron microscope. Observations were also performed on other species with taxoid-type pollen grains.

Key Results

A temporary structure located just above the pore was observed on Cupressus pollen grains, as well as on other taxoid-type pollens. It is hemispheric, layered, and consists of polysaccharides and proteins. The latter are confined to its inner part. Its presence seems to regulate the entrance of water into the grains at the beginning of pollen hydration.

Conclusions

The presence of a temporary structure over the pore of taxoid-type pollen grains was confirmed and its structure was resolved using several stains and observation techniques. This structure plays a role in the first phases of pollen hydration.     

New insights into the pollen morphology of the genus Mutisia (Asteraceae, Mutisieae)

The pollen morphology from 67 collections representing 52 species of Mutisia was analyzed by means of light, scanning electron and transmission electron microscopy. Pollen of Mutisia is comparable to that of the more widespread type found in Mutisiinae. The pollen grains of the genus are characterized by the spheroidal-subprolate to prolate shape, large size, tricolporate aperture, with mesoaperture, exine Mutisia type, with sculpturing microechinate to rugulate or microechinate-rugulate. This basic pollen type is very variable in size, endoaperture shape, and exine thickness of the pollen grains. A new type of arrangement of columellae was observed in pollen of Mutisia section Mutisia (e.g., M. stuebelli, M. microphylla, and M. sodiroi). It is suggested that it might have harmomegathic significance. The pollen morphology and polymorphism are discussed with regard to functional mechanisms and possible evolutionary significance.     

Ultrastructure of the Secondary Egg Envelope of Cyprinodontidae of the Genus Epiplatys Gill, 1862 (Pisces,Teleostei)

Abstract The structure of the secondary egg envelope of seven species of Cyprinodontidae belonging to the genus Epiplatys was observed by transmission and scanning electron microscopy. The transverse structure of the secondary envelope examined by transmission electron microscopy is a constant feature in all the species studied and represents a good criterion for identification. In contrast, the surface structure of the secondary envelope when observed by scanning electron microscopy exhibits a great diversity of form. It is possible to distinguish each of the seven different species by the pattern of ornamentation, the width of the polygons and the size of the granules comprising them on the secondary egg envelope.     

POLLEN MORPHOLOGY IN THE GENUS ERYTHRONIUM (LILIACEAE) AND ITS SYSTEMATIC IMPLICATIONS

Pollen morphology was examined in 40 samples from 19 species in the genus Erythronium (Liliaceae) using scanning (SEM) and transmission electron microscopy (TEM). Pollen grains are monosulcate monads, except for a plant of E. oregonum which has dyad grains. North American and European species are characterized by reticulate exine sculpture composed of various degrees of wavy muri and variably-sized lumina. The most distinctive feature of exine sculpture in the genus is exhibited by the Asian species E. japonicum, which has a unique reticulate pattern composed of striate muri and a distinctive exine structure without columellae. The distinctness of E. japonicum pollen suggests that it has specialized in isolation from species in North America and Europe.     

A reevaluation of the fertilizin hypothesis of sperm agglutination and the description of a novel form of sperm adhesion

The classical isoagglutination of sea urchin sperm by egg jelly is not an agglutination of cells, as proposed by the fertilizin-antifertilizin hypothesis. Sperm motility is required to obtain the isoagglutination of Strongylocentrotus purpuratus sperm, and the sperm do not adhere to each other in the isoagglutination clusters, which cannot be fixed for microscopy and which disperse rapidly into individual cells when sperm motility is inhibited. These observations suggest that isoagglutination is the swarming of freely moving sperm to a common focus and is quite distinct from the agglutination of sperm by known crosslinking agents (antibodies or lectins).A previously unrecognized form of sperm agglutination is described which follows induction of an acrosome reaction by egg jelly, ammonia, or the ionophore A23187 in a suspension of sea urchin or sand dollar sperm. The sperm form rosettes of up to 100 cells in which the newly extended acrosomal processes adhere to each other. Rosettes can form containing sperm of different species, in which the acrosomal processes adhere without species preference.As observed by transmission electron microscopy, the acrosomal process of Lytechinus pictus sperm consists of an acrosomal tubule covered by a sheath of extracellular material. Rosette formation results from attachment between the extracellular materials of adjacent sperm.Less frequently, the acrosomal process of one sperm adheres to the midpiece of another by fusion of the acrosomal tubule and midpiece plasma membranes.     

Dissolution of Autographa californica nuclear polyhedrosis virus polyhedra by the digestive fluid of Trichoplusia ni (Lepidoptera:Noctuidae) larvae

The dissolution of polyhedra of Autographa californica nuclear polyhedrosis virus by digestive fluid collected from 5th stage Trichoplusia ni larvae was studied in vitro. Observations were made at timed intervals using phase contrast microscopy, and scanning and transmission electron microscopy. Dissolution occurred rapidly and in a detectable sequence. Under phase contrast, most polyhedra lost their refringence by 0.5 min. The polyhedra became rounded in appearance with small protuberances on the surface and Brownian movement was observed within. After 1 min, the envelope of most polyhedra had ruptured, releasing the enclosed virions. The protuberances were also observed under the scanning electron microscope after digestion for 0.5 min. Many shell fragments devoid of internal contents were seen after more lengthy digestion. Internal structural changes were revealed by electron microscopy. After 1 min of exposure, polyhedra were observed in all stages of dissolution. By 3 min, only virions, scattered about in heterogeneous material, could be distinguished.     

Re-description of Eubothrium vittevitellatus Mamaev, 1968 (Cestoda: Pseudophyllidea) from sand fish (Trichodon trichodon Tilesius) in Kamchatka Bay with an assessment of its distribution

Eubothrium vittevitellatus is re-described with particular attention being paid to scolex characters seen by scanning electron microscopy in material obtained from the intestines of the sand fish (Trichodon trichodon) from Kamchatka Bay. It is confirmed as a valid species distinguishable from others in the genus by the combined characters of scolex shape, muscle arrangement and position of vitelline follicles. Peculiarities in the distribution and specificity of the species of Eubothrium highlighted by E. vittevitellatus are discussed.     

Palynology and systematics of morinaceae

Pollen grains from all thirteen species of the three genera to be recognised in a forthcoming revision of the Morinaceae, Acanthocalyx, Cryptothladia and Morina, have been investigated by light and scanning electron microscopy. Fresh pollen of M. longifolia has also been studied by light, scanning electron and transmission electron microscopy. Three main pollen types are described and a key provided for their identification. Each pollen type occurs throughout a genus. Further division of two of these pollen types enables groups of species to be recognised. Functional aspects of the pollen are discussed, especially their unique pre-germinative processes. A cladistic analysis of pollen characters provides a hypothesis for their evalution and supports the classification proposed in the recent revision.     

Structure of a microbiol mat at Great Sippewissett Marsh, Cape Cod, Massachusetts

The microzination of phototrophic bacteria in a flat laminated microbiol mat at Great Sippewissett Salt Marsh on Cape Cod, Massachusetts, was studied using a combination of scanning and transmission electron microscopy, light microscopy and photosynthetic pigment analysis. Comparison of pigment content and ultrastructural information from electron microscopy of thin sections allowed us to determine the major groups of photosynthetic bacteria present. The approximately 1-cm-thick mat is located in sandy intertidal sediments of the marsh and comprised four to five distinctly colored layers. The uppermost brown layer contained Lyngbya, Nostoc, Phormidium (cyanobacteria) and Navicula (diatom) species. An intermediate bluish-green layer was dominated by Oscillatoria species. A central pink layer contained purple sulfur bacteria such as Amoebobacter, Thiocapsa, Chromatium and Thiocystis species, Below this was a distinctive orange layer, formed largely by one species of purple sulfur bacteria, Thiocapsa pfennigii. The lowermost and thinnest layer contained green sulfur bacteria of the genus Prosthecochloris, a very small prosthecate species with numerous knobby projections; this layer was not always present. Below this, where pigments were generally absent, were dark gray and black iron sulfide-rich sediments. Remnants of older decayed mats could be found deeper in the sediment. Extensive production of microbial extracellular polymers in all layers appeared to be responsible for attachment of cells to sand grains, for lamination of layers and for structural integrity of the mat as a whole. Below the layer of green sulfur bacteria, binding of sediment by microbial polymers ceased abruptly. Possibly in response to decreasing light penetration, the mean size of bacterial cells decreased in successively deeper layers. In the lowest layer where light penetration was very low, green sulfur bacteria with highly convoluted surfaces occurred. The increase in cell surface area-to-volume ratio may allow such organisms to survive at low light levels.     

Fine Structure of a Silica-Biomineralizing Testate Amoeba,Netzelia tuberculata1

The fine structure of the cytoplasm and the intracytoplasmic origin of siliceous granules and surrounding cement plaques used in constructing the shell wall of Netzelia tuberculata are described. These organisms construct their test from biogenic siliceous particles and sand grains or other foreign particles (including starch grains apparently from algal prey) coated with biogenic silica. The smooth surface texture of the grains, compared to those of other particle-gathering testate amoebae, can be expalained by the deposition of a thin surface layer of silica on the foreign particles incorporated into the wall.     

Pollen morphology in Asiatic species ofTrillium

Pollen grains of five species and two interspecific hybrids ofTrillium from eastern Asia have been examined with scanning electron and transmission electron microscopy. All species from eastern Asia, excludingT. govanianum, are characterized by inaperturate pollen and an unstratified and granulated exine structure. Pollen of the Himalayan species,T. govanianum, is, however, monocolpate and intectate. The palynological evidence suggests that the Asiatic species, excludingT. govanianum, are closely related to each other and toT. erectum in North America, andT. govanianum is independent of the other species in the genus.     

Magnetite biomineralization in termites

Experimental evidence exists for magnetoreception in termites, a major component of the soil macrofauna in many tropical countries. This preliminary study identifies, probably for the first time, the presence of biogenic ferrimagnets (magnetite?) in two species of termite (Nasutitermes exitiosus and Amitermes meridionalis), based on magnetic measurements of whole termite specimens and individual body sections, and analysis by electron microscopy of magnetically extracted grains. The magnetic measurements indicate the presence of very small concentrations of magnetic material, with more magnetic grains in the thorax and abdomen region compared with the head. Magnetic interaction, due to clustering of grains, is also identified by the measurements. Analysis of magnetic extracts by transmission electron microscopy identifies the presence of uniquely ultrafine (10 nm) and unidimensional grains of ferrimagnetic material, unequivocally distinct from any possible extraneous magnetite sources, such as ingested soil. Hence, this provides firm evidence for biogenic formation of this magnetic material by these two termite species. Such ultrafine grains would be superparamagnetic, i.e. incapable of carrying a permanent magnetic moment, unless they were sited in clusters of interacting grains, when some remanence-carrying ability, and hence magnetotaxis, would be possible.     

Lepidoderma cristatosporum, a new species of myxomycete from Australia

A new species of myxomycete, Lepidoderma cristatosporum, is described from Australia. This species is represented by material collected on subantarctic Macquarie Island. Photographs of fruiting bodies and morphological features as observed under light microscopy are provided, along with micrographs of spore ornamentation as observed by scanning electron microscopy. In addition, the new species is compared with other taxa belonging to the genera Lepidoderma and Diderma, especially with the type material of Lepidoderma crustaceum, a very similar species, and Diderma ochraceum and D. sauteri, two species also muscicolous, for which microphotographs are provided.     

Pollen morphology of selected species of the genera <Emphasis Type="Italic">Chrysodracon</Emphasis> and <Emphasis Type="Italic">Dracaena</Emphasis> (Asparagaceae,subfamily Nolinoideae) and its systematic implications

Pollen grains of 3 species from the genus Chrysodracon and 20 species from the genus Dracaena were examined by light, scanning electron and fluorescence microscopy. The basic shape of the pollen grains is subprolate and prolate, but prolate-spheroidal pollen grains may also be found. Pollen of Chrysodracon and Dracaeana is dispersed as monads, rarely as dyads. In terms of size, the pollen grains studied were classified as medium-sized and large. There are two different types of apertures: monosulcate and monoulcerate in Dracaena and monoulcerate in Chrysodracon. The surface of the non-apertural areas is psilate-perforate, irregularly folded, microreticulate and fossulate. Ornamentation of the apertural region is microreticulate, microreticulate-baculate, baculate, psilate-perforate, psilate-perforate-verrucate, granulate and irregularly folded. Irregular perforations are present, and the wall structure is tectate-columellate. Our results suggest that some species of Chrysodracon and Dracaena may be separated based on their pollen grain micromorphology on the distal region.     

SCANNING ELECTRON MICROSCOPY OF RHIZOSHEATHS OF ORYZOPSIS HYMENOIDES

Structural features and microorganisms associated with rhizosheaths (sand grain root sheaths) of Oryzopsis hymenoides were examined by scanning electron microscopy. Rhizosheath structure appears to depend primarily on the extent of root hair growth and the bonding between root hairs and sand grains. Several sources of bonding agents are suggested, but plant products may be the most important. Microorganisms, usually rod forms, were frequently observed in association with coatings, resembling mucilage, on root surfaces and root hairs. The fungus Olpidium and unusual bacterial forms resembling Ancalomicrobium and Hyphomicrobium were observed on or near root surfaces. Mycorrhizae were not observed nor could the presence of actinomycetes be attested to.     

Secretory products of the Malpighian tubules of Cicadellidae (Hemiptera,Membracoidea): an ultrastructural study

The middle segment of the Malpighian tubules (MT), specialized for secretion of proteins and lipids, was investigated by transmission electron microscopy in nymphs and adults of nine cicadellid species (Hemiptera, Cicadellidae). In addition, the external cuticle coated with secretory products of the MT was studied by scanning electron microscopy. The ultimate secretory product found in adult cicadellids, both in the MT and on the cuticle, were intricately structured particles known as brochosomes (BS). These showed significant differences in size, shape and internal structure among species studied. Common features of all BS were a bounding outer membrane and regular cell-like depressions on the surface. Nascent BS develop in numerous Golgi regions as secretory vesicles individually enclosed in larger vacuoles. Definitive structure of BS is acquired during the peculiar post-Golgian maturation. Two basic patterns of the secretion in the MT during ontogenesis were recognized. In Cicadella viridis (L.), Bathysmatophorus reuteri J. Shlb., Graphocraerus ventralis (Fall.) and Doratura impudica Horv. BS are produced and applied onto the cuticle in both adults and nymphs. In contrast, in young nymphs of Vilbasteana oculata (Ldb.), Populicerus nitidissimus (H.-S.), Oncopsis flavicollis (L.) and Ulopa reticulata (F.) the MT are involved in production of various secretions other than BS. The secretory cells in these species undergo a change switching to BS production in the last nymphal instar, so that the BS are applied onto the cuticle for the first time only in freshly molted adults. The secretory patterns differ among subfamilies. The observed diversity of products suggests that the protective water- or feces-repellent function proposed for BS cannot completely explain the adaptive significance of the secretory specialization of the MT in cicadellids.     

The structure of lerps: Carbohydrate,lipid, and protein components

Chemical analyses and studies by scanning electron microscopy were made of the lerps of Lasiopsylla rotundipennis and of Cardiaspina albitextura. Unlike the open, lace-like structure of the lerp of C. albitextura, the lerp of L. rotundipennis is a solid shell with a surface structure of repeated parallel arcs. Lerps of both species consist mainly of starch, but also contain protein and lipid. In addition, the lerp of L. rotundipennis is associated with proteinaceous spiral filaments secreted by glands on the ventral abdomen.     

Pollen Morphology of the Aceraceae

Pollen of 40 Acer taxa and one species of Dipteronia were examined by light, scanning and transmission electron microscopy. Pollen grains in both genera are tricolpate or tricolporate of prolate to nearly spheroidal shape. Based on sexine pattern, four major pollen types were recognized and include striate grains, rugulose grains, microreticulate grains, and granular grains. Although the family appears to be rather stenopalynous, several useful taxonomic variations occur.