Fine structure of the host-fungus interface in orchid mycorrhiza

Summary Electron microscopy of protocorms of Dactylorhiza purpurella infected with a symbiotic Rhizoctonia sp. showed that the intracellular hyphae examined did not penetrate the plasmalemma of the host cell. Walls of hyphae within cells bore many hemispherical protuberances over which the host plasmalemma was closely pressed. we estimate that these protuberances would increase the area of contact between hyphae and host plasmalemma by about 15%. They were not found on hyphae growing on agar. Except for these protuberances, and some vesicles or tubules which invaginated the fungus plasmalemma, no other structures were seen which could be suggested to be adaptations to transport across the living fungus-host interface.     

Multinucleate transfer cells induced in coleus roots by the root-knot nematode,Meloidogyne arenaria

Summary The occurrence and position of wall protuberances in giant cells induced in coleus roots by the root-knot nematodeMeloidogyne arenaria is described, and the structure and function of giant cells is compared with that of syncytia induced by cyst-nematodes.Extensive protuberance development occurs on walls of giant cells adjacent to xylem vessels. Protuberances are less well developed next to sieve elements, and almost absent next to parenchyma cells. On walls between giant cells they occur on both sides or only one side. The formation of protuberances indicates that giant cells are multinucleate transfer cells. The position of protuberances marks the wall area where solutes enter the cell. Solutes are obtained from xylem and phloem elements, and the position of protuberances at the junction between giant cells and vascular elements indicates an extensive flow of solutes along cell walls. The observations support the hypothesis that wall protuberances form as a result of selective solute flow across the plasmalemma.No cell wall dissolution was observed, although wall gaps may occur between giant cells as a result of breakage during rapid cell expansion.     

Fine structures on the surface of nuptial pads of male hylid and rhacophorid frogs

Nuptial pads, secondary sexual characteristics of male frogs, develop on the first digit of the hand of Hyla japonica in the family Hylidae and of Rhacophorus schlegelii in the family Rhacophoridae, and on both the first and second digits of the rhacophorids Buergeria buergeri and B. japonica. By scanning electron microscopy (SEM), it was seen that numerous mounds covered the surface of the pads. Mounds were similarly hemispherical in R. schlegelii and B. buergeri and flat in B. japonica. The mounds of H. japonica were irregular in shape and size and some of them stood in rows. Fine columnar protuberances were present all over the surfaces of the mounds in this species. Numerous peg-like protuberances projected radially upward from the top of the mounds in B. buergeri and B. japonica. Irregular-shaped, leaf-like protuberances bearing knobby or rod-shaped apical protrusions were present on the top of the mounds in R. schlegelii. In pads observed by transmission electron microscopy, the outermost epithelial monolayer of the mounds was generally thick, especially at the top, compared to that of the rest of the skin. Epidermal cells in this layer were well keratinized, devoid of organelles, and contained closely packed, fine filaments within a dense matrix. Apical accessory protuberances projecting from the outermost cells were also packed with dense filamentous materials, showing rigid comb-like structures. © 1994 Wiley-Liss, Inc.     

Somatic meiosis in the life history of Bonnemaisonia asparagoides and Bonnemaisonia clavata (Bonnemaisoniales,Rhodophyta) from the Iberian peninsula

Carpospores isolated from Bonnemaisonia asparagoides and Bonnemaisonia clavata (Bonnemaisoniaceae, Rhodophyta) and grown in culture developed into their respective ‘Hymenoclonium’ prostrate phases. In both species, young gametophytes were initiated directly on the prostrate phase from tetrasporangia-like protuberances. Comparison of the relative fluorescence area (rfa) of nuclear DNA over the sequence of life-history stages indicated that the lowest ploidy levels (1–2C) occurred in the gametophytes, whereas the lowest ploidy levels in the prostrate phases were 2–4C. Rfa data demonstrated that meiosis occurred in the tetrasporangia-like protuberances where 1C values were recorded. The present observations establish that B. asparagoides and B. clavata have a heteromorphic diplohaplontic life history, which involves a haploid gametophyte produced directly on a diploid prostate phase after somatic meiosis. We conclude that the life history of these taxa corresponds to the Lemanea-type. This indicates that the life history of several Bonnemaisoniales with a ‘Hymenoclonium’ phase but lacking tetrasporangia requires re-investigation.     

Scanning electron microscopy of ascospores of Debaryomyces and Saccharomyces

Ascospores from species of Debaryomyces and the Torulaspora-group of Saccharomyces were examined by scanning electron microscopy. Ornamentation on ascospores of D. hansenii varied from short to long interconnected ridges or broad based, elongated conical protuberances. A spiral ridge system was detected on the ascospores of D. marama, but wart-like protuberances occurred on those of D. cantarellii, D. castellii, D. coudertii, D. formicarius, D. phaffii, D. vanriji and D. yarrowii. Ascospores of D. halotolerans did not have protuberances and the species appears to be identical with Pichia farinosa. Wart-like protuberances also were found on ascospores of S. delbrueckii, S. microellipsodes, S. rosei, S. inconspicuus, S. fermentati, S. montanus and S. vafer, but the ascospore surface of S. pretoriensis was covered by fine ridges. Short tapered ridges covered the ascospores of S. kloeckerianus.     

Ultrastructure of chloroplast protuberances in rice leaves preserved by high-pressure freezing

High-pressure freezing and freeze substitution were used to prepare leaves of rice (Oryza sativa L.) for ultrastructural analysis. Under these preparative conditions, plastid-derived stroma-containing protuberances were preserved and described with the electron microscope for the first time. Similar protuberances were observed previously only in living cells examined with the light microscope. Infoldings of the chloroplast inner envelope were a prominent ultrastructural feature of protuberances. Infoldings were also observed in the main body of the chloroplasts and sometimes appeared contiguous with thylakoid membranes. Protuberances also contained infoldings in the form of bifurcated tubules. Apparent interconnection between protuberances of adjacent plastids was observed only in one instance. A distinct gradient in the staining density of thylakoid lumina appeared to be a function of grana position and orientation relative to the cell wall. Immunocytochemistry was used to determine that the stroma within protuberances contained 1,5-bisphosphate carboxylase/oxygenase enzyme. Received: 21 December 1998 / Accepted: 29 January 1999     

Organization of the spinnerets and spigots in the orb web spider,Argiope bruennichi (Araneae: Araneidae)

Although the basic taxonomic characteristics usually remain unchanged, some spinning apparatuses undergo consistent adaptive variations. As the presence of additional protuberances known as nubbins and tartipores have caused disagreements regarding some Araneidae spiders, more detailed definitions on the cuticular structures have recently been proposed. Reflecting this definition, microstructural organization of silk spinning apparatuses in the orb web spider Argiope bruennichi were reconsidered using field emission scanning electron microscopy. Among the seven kinds of functional spigots in females, it was revealed that two types (major ampullates and pyrifoms) are located on anterior spinnerets and another five types are distributed on median (minor ampullates, tubuliforms and aciniforms) or posterior (tubuliforms, flagelliforms, aggregates and aciniforms) spinnerets, respectively. In addition to functional spigots, cuticular remnants of the nubbins and the tartipores were found on the spinning fields, but the number of tartipores on each spinneret varied among individuals based on maturity. Nevertheless, three kinds of cuticular protuberances of ampullate silk glands were clearly visible at both the anterior and median spinnerets.     

In vitro studies on the anatomy and morphology of bud regeneration in melon cotyledons

Summary The anatomy and morphology of bud regeneration were investigated in melon (Cucumis melo L.) cv. Galia, which regenerates in vitro only by direct organogenesis from the cotyledon explant. Explants were cut from the cotyledon proximal to the apex from 3-d-old in vitro seedlings. After 3 d on Murashige and Skoog medium with N⁶-benzyladenine, cell division can be observed in the epidermal layer on the adaxial side in the center of the explant, near the most proximal (wounded) cut edge. Over the next week, the area of the meristem increases laterally. Additional cell layers are added to the meristematic area by cell division in the epidermis. In places the epidermis remains active in cell division. Alongside those active areas there are zones where the epidermis has become inactive, although the subepidermal layers continue to divide. In transverse section, the explant now has small protuberances on the adaxial surface. After 10 d on cytokinin-containing medium, the first signs of development are visible on the adaxial surface adjacent to the proximal cut edge. The protuberances observed after 10 d are neither primordia nor buds, although some meristematic bulges are observed. The first regenerated shoot buds are observed histologically after 15 d, by which time the surface has many protuberances and some small leaves. The first shoot is found by histology after 22 d. By this time the surface is covered with protrusions and leaves, mostly without accompanying buds. The leaves may be produced from the protrusions initially visible after 10 d.     

Intercellular protuberances in the ground tissue ofCocos nucifera L.

Summary Prolific filamentous intercellular protuberances have been observed in the intercellular spaces of the ground parenchyma tissue in the stems ofCocos nucifera. They are visually similar to some intercellular material reported in several other plant tissues but their chemical composition is unknown. Tests for lignin, cellulose, callose, suberin and waxes have proved negative and those for pectin inconclusive. The amount of intercellular material is closely related to the thickness of the parenchyma cell wall and the protuberances appear to be produced continuously by an active cytoplasm.     

Ultrastructure of the sporangiospore of Piptocephalis unispora (Mucorales)

Sporangiospore structure in Piptocephalis unispora Benjamin was studied using light microscopy, freeze-etching, scanning and transmission electron microscopy, and compared with that of other members of the Mucorales. A merosporangial wall, plasmalemmal invaginations, and wall protuberances were demonstrated in sections and their possible significance discussed.     

Formation and reversion ofSchizosaccharomyces pombe cells with apical protoplast protuberances

Lytic enzymes from the hepatopancreas ofHelix pomatia do not induce a uniform digestion of the cell wall ofSchizosaccharomyces pombe over the entire cell surface. Perforations are formed in the growth zones through which a protoplast can locally protrude. Conditions were found under which the frequency of formation of apical protoplast protuberances is higher than 90% cells with such protuberances can reverse to normally multiplying cells. Translated by J. Spížek     

Meiosis,basidiospore development and post-meiotic mitosis in the basidiomycete,Phallus impudicus

The meiotic spindles of Phallus impudicus had a similar ultrastructure to those seen in other basidiomycetes. After meiosis the basidal apex differentiated to form a number of broadly based protuberances which subsequently developed into basidiospores (up to 9 per basidium). The nuclei then underwent a post-meiotic mitosis within the cytoplasm of each basidiospore. After this mitosis one nucleus remained in the basidiospore and a complete septum developed at the base. The significance of this arrangement of meiosis, spore production and post-meiotic mitosis is discussed with respect to the taxonomy and life cycle of this unusual basidiomycete.     

Transferzellen im Xylem derValerianaceae

Stems, incl. rhizomes, and roots of 42 species ofValerianaceae were investigated in order to reveal the occurrence, structure and distribution of xylem transfer cells. Within nodes and internodes their frequency, distribution and gradients of development are similar to other families. — Within the secondary xylem of some species transfer cells can develop from cambial derivates, inValeriana tuberosa andPatrinia villosa even from pith cells. Within the turnip ofV. tuberosa transfer cells are very frequent and well developed. Here, after degradation of the cell-wall ingrowths they can be redifferentiated into storage cells which usually contain starch grains (Hüllenstärkekörner). In the transitional zone between stem and root of some predominantly herbaceous taxa transfer cells are often very frequent and form large protuberances before they degrade and lignify. SEM observations inValeriana decussata show that the cell-wall ingrowths are degradated at the beginning of lignification with the exception of brush-like protuberances remaining in the half-bordered pit-pairs. During the subsequent process of lignification the simple pits of a wall adjacent to a vessel can be transformed into corresponding pit-pairs. In this case the residues of the protuberances within the pit chamber can be transformed into incrustations similar to the vestures of bordered pits described byBailey (1933). Structural similarities between the brush-like protuberances in the half-bordered pits of theValeriana transfer cells and the ingrowths found inLauraceae (Castro 1982, 1985) are evident. Supposedly, all the cambial derivatives inValerianaceae can develop protuberances at least within their pits. Thus, it appears possible to interpret the vestures of the bordered pits as rudimentary protuberances, and to suggest that they have a specific function in the selective transport of solutes.

---

Transferzellen im Xylem derValerianaceae

     

The ultrastructure of the salt gland of Spartina foliosa

Summary The salt gland in Spartina foliosa is composed of two cells, a large basal cell and a smaller, dome-shaped cap cell which is located on a neck-like protrusion of the basal cell. There is no cuticular layer separating the salt gland from the mesophyll tissue. The basal cell has dense cytoplasm which contains numerous mitochondria, rod-like wall protuberances, and infoldings of the plasmalemma which extend into the basal cell and partition the basal cell cytoplasm. The protuberances originate on the wall between the basal and the cap cells and are isolated from the basal-cell cytoplasm by the infoldings of the plasmalemma. While the cap cell has no partitioning membrane system or wall protuberances, it resembles the basal cell by having dense cytoplasm and numerous mitochondria.The basal cell seems to be designed for efficient movement of ions toward the cap cell. The long, dead-end extracellular channels in the basal cell of Spartina appear comparable to surface specializations seen in the secreting epithelium of animal cells which carry out solute-linked water transport. The number of mitochondria and their close association with the plasmalemma extensions suggest that they have an important role in the transfer of ions through the basal cell.The accumulated ions would move into the extracellular spaces along an osomotic gradient where the accompanying passive flow of water would move the ions into the cap-cell wall and from there the solution would pass out through the pores in the cuticle.     

Architecture of the cell wall of a green alga,Oocystis apiculata

Summary The cell wall of a green alga,Oocystis apiculata, was visualized by electron microscopy after preparation of samples by rapid-freezing and deep-etching techniques. The extracellular spaces clearly showed a random network of dense fibrils of approximately 6.4 nm in diameter. The cell wall was composed of three distinct layers: an outer layer with a smooth appearance and many protuberances on its outermost surface; a middle layer with criss-crossed cellulose microfibrils of approximately 15–17 nm in diameter; and an inner layer with many pores between anastomosing fibers of 8–10 nm in diameter. Both the outer and the inner layer seemed to be composed of amorphous material. Cross-bridges of approximately 4.2 nm in diameter were visualized between adjacent microfibrils by the same techniques. The cross-bridges were easily distinguished from cellulose microfibrils by differences in their dimensions.     

The surface microstructure of marine and terrestrial isopoda (Crustacea,Peracarida)

Summary The microstructure of the surface of thirteen marine littoral and two terrestrial isopods was investigated by scanning electron microscopy. A great diversity of surface ornamentation is present, including non-sensory microscales, pits, tubercles, and ridges, and sensory tricorns, pit organs, pores, papillae and setae. Microscales are common features of the integument surface; their shape and size are highly variable. Tricorns were not observed on the marine littoral isopods. Several hitherto undescribed structures were observed including spade-like projections from the tergite surface of Oniscus asellus, hair-like filaments associated with the microscales of Jaera and ridged conical protuberances on Edotea triloba and E. montosa. The possible function of certain surface microstructures is discussed.     

Ultrastructural features of the salt gland of Tamarix aphylla L.

Summary The salt gland in Tamarix is a complex of eight cells composed of two inner, vacuolate, collecting cells and six outer, densely cytoplasmic, secretory cells. The secretory cells are completely enclosed by a cuticular layer except along part of the walls between the collecting cells and the inner secretory cell. This non-cuticularized wall region is termed the transfusion are (Ruhland, 1915) and numerous plasmodesmata connect the inner secretory cells with the collecting cells in this area. Plasmodesmata also connect the collecting cells with the adjacent mesophyll cells.There are numerous mitochondria in the secretory cells and in different glands they show wide variation in form. In some glands wall protuberances extend into the secretory cells forming a labyrinth-like structure; however, in other glands the protuberances are not extensively developed. Numerous small vacuoles are found in some glands and these generally are distributed around the periphery of the secretory cells in association with the wall protuberances. Further, an unusual structure or interfacial apparatus is located along the anticlinal walls of the inner secretory cells. The general structure of the gland including the cuticular encasement, connecting plasmodesmata, interfacial apparatus, and variations in mitochondria, vacuoles, and wall structures are discussed in relation to general glandular function.     

Morphological plasticity associated with environmental hypoxia in characiform fishes from neotropical floodplain lakes

The ability to develop reversible dermal extensions on the lower jaw in some South American characiform fishes has been proposed as a way to optimize the performance of aquatic surface respiration (ASR) during hypoxic conditions. These structures are formed by edema of the hypodermal tissues and can develop in a large proportion of individuals inhabiting a lake within a few hours following daily changes in dissolved oxygen. Our study report the development of dermal lip protuberances in eleven species of characiform fishes associated with periods of strong environmental hypoxia in floodplain lakes of Salado River, Argentina. Protuberances occurred in different basic forms in fishes with divergent head morphology (genera Astyanax, Ctenobrycon, Aphyocharax, Brycon, Mylossoma, Triportheus, Oligosarcus and Acestrorhynchus). The discovery of dermal projections on the anterior border of maxillary bone extends the known range of structures affected by lip protuberances. Dermal structures began to develop simultaneously in both jaws below dissolved oxygen (DO) concentrations of 1.20–1.75 mgl⁻¹ and rose in a steep manner as oxygen level decreased. The degree of morphological plasticity differed among traits and species. The shape of response of morphology to DO was similar to that previously reported on ASR, providing additional evidence about the functional link between these traits. Our results suggests that dermal lip protuberances are widely spread among characiform fishes, affecting several mouth structures. The different types of protuberances would make up for the limitations imposed by body size and mouth shape and position on the performance of ASR in fishes with divergent morphology.     

New branched Porolithon species (Corallinales,Rhodophyta) from the Great Barrier Reef,Coral Sea,and Lord Howe Island

Porolithon is one of the most ecologically important genera of tropical and subtropical crustose (non-geniculate) coralline algae growing abundantly along the shallow margins of coral reefs and functioning to cement reef frameworks. Thalli of branched, fruticose Porolithon specimens from the Indo-Pacific Ocean traditionally have been called P. gardineri, while massive, columnar forms have been called P. craspedium. Sequence comparisons of the rbcL gene both from type specimens of P. gardineri and P. craspedium and from field-collected specimens demonstrate that neither species is present in east Australia and instead resolve into four unique genetic lineages. Porolithon howensis sp. nov. forms columnar protuberances and loosely attached margins and occurs predominantly at Lord Howe Island; P. lobulatum sp. nov. has fruticose to clavate forms and free margins that are lobed and occurs in the Coral Sea and on the Great Barrier Reef (GBR); P. parvulum sp. nov. has short (<2 cm), unbranched protuberances and attached margins and is restricted to the central and southern GBR; and P. pinnaculum sp. nov. has a mountain-like, columnar morphology and occurs on oceanic Coral Sea reefs. A rbcL gene sequence of the isotype of P. castellum demonstrates it is a different species from other columnar species. In addition to the diagnostic rbcL and psbA marker sequences, the four new species may be distinguished by a combination of features including thallus growth form, margin shape (attached or unattached), and medullary system (coaxial or plumose). Porolithon species, because of their ecological importance and sensitivity to ocean acidification, need urgent documentation of their taxonomic diversity.