Subapical Cell Research Articles

A morphologically structured model for penicillin production.

A morphologically structured model is proposed to describe penicillin production in fed-batch cultivations. The model accounts for the effects of dissolved oxygen on cell growth and penicillin production and variations in volume fractions of abiotic and biotic phases due to biomass formation. Penicillin production is considered to occur in the subapical hyphal cell compartment and to be affected by availability of glucose and oxygen. As it stands, the model provides a wide range of applicability in terms of operating conditions. The model has been tested for various conditions and has given satisfactory results. A series of glucose feeding profiles have been considered to demonstrate the capabilities of the proposed model. It is concluded that the model may be valuable for the interpretation of experimental data collected specifically for metabolic flux analysis during fed-batch cultivation because the elements of measured specific production rates are determined from measurements of the concentrations of the components and their mass balances. The proposed model may be further used for developing control strategies and model order reduction algorithms.

Reappraisal of the type species of Polysiphonia (Rhodomelaceae, Rhodophyta)

The genus Polysiphonia Greville, nom. cons., has had a long and confused nomenclatural history. At present, Polysiphonia has a wide circumscription, including at least 200 species, but it is heterogeneous in many vegetative and reproductive developmental features. Central to any re-evaluation of the genus is a detailed examination of the type species of Polysiphonia, P. urceolata (Lightfoot ex Dillwyn) Greville, which is conspecific with P. stricta (Dillwyn) Greville. We here report on the vegetative and reproductive morphology of P. stricta, including P. urceolata, based on type and other material from the British Isles. Thalli consist of prostrate and erect ecorticate axes with four pericentral cells, attached by unicellular rhizoids remaining in open connection with pericentral cells. Prostrate axes lack vegetative trichoblasts ; trichoblasts occur seasonally on erect axes. Branch initials are cut off from the subapical cell at intervals of four or five segments in dichotomous and alternating pairs rather than being formed from each axial cell in the spiral pattern typical of most species of Polysiphonia. Spermatangial branch initials, which are trichoblast homologues, are produced directly from each axial cell at the tips of erect branches, not subtended by trichoblasts, and have two- to five-celled sterile tips when mature. The mature carpogonial branch is four-celled with a two-celled first sterile group and a one-celled second sterile group. Following presumed fertilization, direct fusion apparently takes place between carpogonium and auxiliary cell; mature cystocarps are usually urceolate. Tetrasporangia are formed from the third pericentral cell, in straight series, and have two pre-sporangial cover cells. Previous accounts of a third, post-sporangial cover cell could not be substantiated. P. stricta and a small group of other Polysiphonia species differ in several important respects from most members of the genus, which have rhizoids cut off from pericentral cells by a cell division, abundant trichoblasts, spirally arranged tetrasporangia and a post-sporangial cover cell. The branching pattern of P. stricta highlights the difficulties of distinguishing between the tribes Polysiphonieae and Pterosiphonieae.

Gibberellins and Subapical Cell Divisions in Relation to Bud Set and Bud Break in Salix pentandra.

In young plants of Salix pentandra, a temperate zone deciduous woody species, elongation growth ceases and a terminal bud is formed at day lengths shorter than a critical length. This is the first step in dormancy development, making survival under harsh winter conditions possible. Early studies strongly indicate that gibberellin is involved in the photoperiodic control of bud set and bud break. GA(1) action was studied by application under short days to plants where cessation of shoot elongation had occurred, followed by subsequent anatomic investigations of shoot tips. Under short days the frequency of cell division decreased rapidly along with the earlier observed decrease in GA(1) levels. Application of GA(1) to short-day-induced terminal buds rapidly stimulated cell division in apices several days before visible shoot elongation in response to this treatment was observed. One day after GA(1) application a fourfold increase in cell division frequency in apices was observed, increasing to a maximum of sevenfold 2 days after application. Long-day treatment leading to induction of bud break after about 4-6 days was followed by slowly increasing frequency of cell divisions. In earlier studies of this species, short days and gibberellins had no effect on cell elongation. These data show that increased GA(1) content, by application or long-day treatment, results in increased frequency of mitosis. This strongly indicates that GA(1) affects stem elongation in connection with bud set and bud break primarily by affecting cell divisions in subapical tissues.

Rapid downregulation of rat renal Na/P(i) cotransporter in response to parathyroid hormone involves microtubule rearrangement.

Renal proximal tubule cells express in their apical brush border membrane (BBM) a Na/P(i) cotransporter type IIa that is rapidly downregulated in response to parathyroid hormone (PTH). We used the rat renal Na/P(i) cotransporter type IIa (NaPi-2) as an in vivo model to assess early cellular events in the rapid downregulation of this transporter. When rats were treated with PTH for 15 minutes, NaPi-2 abundance in the BBM was decreased. In parallel, transporter accumulated in intracellular vesicles. Concomitantly, microtubules (MTs) were found to form dense bundles of apical-to-basal orientation. After 60 minutes of PTH action, the cells were vastly depleted of NaPi-2, whereas their microtubular cytoskeleton had returned to its normal appearance. Prevention of MT rearrangement by taxol resulted in accumulation of NaPi-2 in the subapical cell portion after 15 minutes and a strong delay in depletion of intracellular transporter after 60 minutes of PTH action. Furthermore, the subapical accumulation of NaPi-2 was associated with the expansion of dense apical tubules of the subapical endocytic apparatus (SEA). Depolymerization of MTs by colchicine likewise caused a retardation of intracellular NaPi-2 depletion. These results suggest that NaPi-2 is downregulated in response to PTH through a rapid endocytic process in 2 separate steps: (a) internalization of the transporter into the SEA, and (b) its delivery to degradative organelles by a trafficking mechanism whose efficiency depends on a taxol-sensitive rearrangement of MTs.

Hyp loci control cell pattern formation in the vegetative mycelium of Aspergillus nidulans.

Aspergillus nidulans grows by apical extension of multinucleate cells called hyphae that are subdivided by the insertion of crosswalls called septa. Apical cells vary in length and number of nuclei, whereas subapical cells are typically 40 microm long with three to four nuclei. Apical cells have active mitotic cycles, whereas subapical cells are arrested for growth and mitosis until branch formation reinitiates tip growth and nuclear divisions. This multicellular growth pattern requires coordination between localized growth, nuclear division, and septation. We searched a temperature-sensitive mutant collection for strains with conditional defects in growth patterning and identified six mutants (designated hyp for hypercellular). The identified hyp mutations are nonlethal, recessive defects in five unlinked genes (hypA-hypE). Phenotypic analyses showed that these hyp mutants have aberrant patterns of septation and show defects in polarity establishment and tip growth, but they have normal nuclear division cycles and can complete the asexual growth cycle at restrictive temperature. Temperature shift analysis revealed that hypD and hypE play general roles in hyphal morphogenesis, since inactivation of these genes resulted in a general widening of apical and subapical cells. Interestingly, loss of hypA or hypB function lead to a cessation of apical cell growth but activated isotropic growth and mitosis in subapical cells. The inferred functions of hypA and hypB suggest a mechanism for coordinating apical growth, subapical cell arrest, and mitosis in A. nidulans.

The Two Nuclei in the Dikaryon of the HomobasidiomyceteCoprinus cinereusChange Position after Each Conjugate Division

We constructed a common-ABdiploid strain ofCoprinus cinereusand mated this to a compatible haploid strain to construct a diploid–haploid dikaryon. We examined the positions of the diploid and haploid nuclei in the apical and subapical cells of the dikaryon by fluorescence microscopy and microfluorometry. In 60% of apical cells the leading nucleus (the nucleus proximal to the hyphal apex) was diploid and the second nucleus (the nucleus distal to the apex) was haploid, whereas in the remaining 40% of apical cells the order of the two nuclei was reversed. It was also observed that in 97% of hyphae examined the order of the diploid and haploid nuclei was reversed between the apical cell and the subapical cell. Based on these observations, we conclude that the two nuclei alternate in taking the leading and second positions in the apical cell at almost every conjugate division in the dikaryon.

Immunolocalization of tubulin and actin in thick‐sectioned fungal hyphae after freeze‐substitution fixation and methacrylate de‐embedment

Immunolocalizations in whole mounts of walled cells require an empirically derived, species‐specific permeabilization strategy. Particularly when cell walls are recalcitrant to enzymatic digestion, as with many fungi, permeabilization can degrade structure and reduce or destroy antigenicity. To avoid these potential problems, hyphae were freeze‐substituted, embedded in a methacrylate resin, thick‐sectioned and de‐embedded prior to immunolocalization. The cytoskeletal proteins actin and β‐tubulin were labelled via indirect immunofluorescence in hyphal tip cells of Magnaporthe grisea, and Trichoderma viride. Well‐defined punctate actin plaques were observed concentrated at the subapical cell periphery in both species, especially near the hypha–substratum interface. In addition, a Spitzenkörper core and less intense cytoplasmic binding were observed. Immunoelectron microscopy confirmed localization of actin in the Spitzenkörper core and filasomes. β‐Tubulin was immunolocalized as both linear arrays and punctate dots via epifluorescence microscopy. Analysis of 450–550‐nm‐thick serial sections contributed to improved resolution by the reduction of out‐of‐focus blur. Overall, the freeze substitution methacrylate de‐embedment technique provided superior preservation, serial section analysis, and improved antibody penetration and resolution of these cytoskeletal proteins. The technique will be a valuable tool for use with a variety of reporter molecules in cells of fungi.

Sexual plants of Diplothamnion jolyi (Ceramiaceae, Rhodophyta) from the Canary Islands

Sexual plants of Diplothamnion jolyi van den Hoek (Ceramiaceae, Rhodophyta) are described for the first time. Sterile plants and monoecious gametophytes were obtained. Procarps are produced subterminally on indeterminate branches in which a three-celled fertile axis is formed at the apex. The subapical cell produces the supporting cell and a sterile pericentral cell. The supporting cell cuts off a lateral four-celled carpogonial branch and a terminal sterile cell. Procarp structure, early post-fertilization stages and mature carposporophytes were observed. Spermatangial heads are formed adaxially at the distal ends of whorl branchlet cells. Spermatangial heads are composed of 2 axial cells that cut off pericentral cells or spermatangial mother cells. Spermatangia are terminal. These features support the placement of D. jolyi in the genus Diplothamnion Joly et Yamaguishi (tribe Sphondylothamnieae).

A proposal to resurrect the tribe Monosporeae Schmitz et Hauptfleisch, with a description of Tanakaella itonoi sp. nov. (Ceramiaceae, Rhodophyta) from southern and western Australia

The tribe Monosporeae (Ceramiaceae, Rhodophyta) of Schmitz & Hauptfleischis resurrected to include Monosporus Solier, Mazoyerella Gordon-Mills et Womersley, Tanakaella Itono, Deucalion Huisman et Kraft, Anisoschizus Huisman et Kraft, Guiryella Huisman et Kraft and Desikacharyella Subramanian. These genera all produce multinucleate, uni- to tricellular asexual propagules. Tetrasporangia or polysporangia may occur. Where females are known, the procarp is formed on the subapical cell of the fertile branchlet and (except in Deucalion) some or all of the sterile cells of the procarp divide to produce an inner involucre which surrounds the young gonimoblast. New information is presented on several of the genera. Included are a description of Tanakaella itonoi sp. nov., reproductive details of Anisoschizus post-fertilization details of Deucalion and sporangial, procarp and spermatangial details of Monosporus australis (Harvey) J. Agardh. Tanakaella itonoi sp. nov. differs from T. japonica Itono (the type of the genus, from Japan) in details of its involucral initiation. In T. itonoi one of the sterile pericentral cells remains undivided following fertilization and is not involved in the production of involucral branches; in T. japonica the sterile cell on the supporting cell does not divide.

A cell surface-associated centrosomal layer of microtubule-organizing material in the inner pillar cell of the mouse cochlea.

This investigation provides evidence that pericentriolar material is divorced from the immediate vicinities of centrioles and becomes functionally associated with the plasmalemma during the differentiation of a mammalian cell type. Such events occur prior to the assembly of large transcellular microtubule bundles in columnar epithelial cells called inner pillar cells in the mouse organ of Corti. The microtubules do not radiate from a typical centrosome and its centrioles. They elongate from a microtubule-organizing centre (MTOC), which is deployed as a subapical cell surface-associated layer in each cell. Most of the dense material of this layer, and the tops of most of the microtubules, are initially concentrated around the sides of a cell about 1 microns below its apical surface. In addition, a pair of centrioles is located above the layer, which acts as if it is a pericellular concentration of the pericentriolar material of a modified centrosome. Although microtubule nucleation takes place in a centrosome-like region, 13 protofilament fidelity is not exercised. Most of the microtubules have 15 protofilaments. Microtubule assembly progresses in these cells after the organ of Corti has been isolated for in vitro culture. However, large numbers of microtubules elongate from pericentriolar material juxtaposed against the centrioles. Hence, there is some reversion by the centrosomes of cultured cells to the operational configuration regarded as typical for animal tissue cells in general.

Location of branches within the apical hyphal region of Streptomyces granaticolor mycelia.

The location of branches (ramifications) within the apical hyphal region of Streptomyces granaticolor mycelia was studied in dependence on the specific growth rate by using batch and chemostat cultures. The site where a new branch emerged was correlated to the neighboured elongation sites (e-sites) as well as to the septae. In dependence on the growth rate the distance from a newly formed branch (i.e. e-site) to the apical e-site (tip of the main hypha) changed from 12 to 44 microns and to the e-site on the tip of the preceding neighboured branch from 12 to 27 microns. Thus, except for the slowest grown culture, the new branching site in the apical hyphal region did not represent the midst between the two preexisting e-sites. Comparing branching and septation sites, the data indicated a close correlation between them, if the respective mean values of whole populations were determined. But regarding individual hyphae, only 4-39%--depending on the growth rate--of the apical branches were directly neighboured to a septum. The remaining percentage was situated at one of several potential branching sites, the number of which per subapical cell corresponded to the number of nucleoids.

Fate of the subapical cell in Streptomyces granaticolor mycelia

AbstractIn stained Streptomyces granaticolor mycelia the fate of the subapical cell (c2) formed periodically after each septation of the apical cell (c1) was analzyed. From the time of birth of c2, the intervals until the starts of first and second branching, the doubling of length by branch growth, and septation were determined. Since five cultures grown at different growth rates were used, the intervals were expressed in relation to the interseptation time of c1 (T) of the respective culture. With few exceptions, the determined values were rather independent of the growth rate. On average, the fate of c2 was: start of branching at 0.7 T, doubling in length at 1.4 T, and septation at 1.7 T, meaning that septation of c1 and c2 did not occur synchronously. A second branch was formed 1.7 T after the first, i.e. at the same interval between the first (in c1) and second (in c2) septation.The site of septation was either more or less median within the original c2‐length, or within the branch, adjacent to the branching site. The percentage of the former was higher in cultures showing delayed branching. Generally, the median position of septation prevailed. As a consequence, the branched c2 was divided into two differently sized and shaped daughter cells. On average, the branch‐receiving daughter was about 2.5 times larger than the branchless daughter.The increase of the frequency of septation within the original c2 cells was followed for five T‐times. Rate and degree of increase was dependent on the growth rate or on the original length of c2. As a result, within all cultures the interseptal distance within the main hyphae approached a length of about 5 μm.

Diplothamnion gordoniae sp. nov. (Ceramiaceae, Rhodophyta) from Rottnest Island, Western Australia

Diplothamnion gordoniae sp. nov. (Ceramiaceae, Rhodophyta) is erected for a minute, filamentous epiphyte from Rottnest Island, Western Australia. The new species produces uncorticated upright axes with opposite-distichous to slightly decussate branching that become secondarily prostrate and anchored by adventitious rhizoids arising from each axial cell. Procarps are formed subterminally on indeterminate branches, in which three shorter, specialized cells are formed at the apices. The subapical cell of the fertile axis produces two pericentral cells, one of which acts as the supporting cell and cuts off a lateral four-celled carpogonial branch and a terminal sterile cell. After fertilization the auxiliary cell is cut off from the supporting cell and produces 2–3 gonimolobes. Inner involucral branches arise from the apical cell, sterile pericentral cell and sterile cell on the supporting cell. The basal cell of the single vegetative branch on the hypogenous cell forms a secondary connection with the subhypogenous cell, thereafter acting as an outer involucral branch. Two new, post-fertilization outer involucral branches arise from the subhypogenous cell, which therefore supports five branches (two normal vegetative branches, one pre-existing branch secondarily connected from the hypogenous cell, and two new branches). Tetrasporangia with tetrahedrally-arranged spores arise singly or in pairs at the distal ends of lateral branch cells. Compact spermatangial heads arise singly in similar positions. Diplothamnion gordoniae differs from the previously described species of the genus in tetrasporangial arrangement, branching pattern and size of vegetative cells. Post-fertilization events for the genus are described for the first time and confirm its placement in the tribe Sphondylothammeae.

The genusCompsothamnionellaItono (Ceramiaceae, Rhodophyta) on the South African coast

SUMMARY Evidence is presented for the occurrence of one species of Compsothamnionella on the coast of the eastern Cape Province, South Africa. Compsothamnionella is once more separated from Pleonosporium, the chief differences being: (i) a more complex cortication in Compsothamnionella, involving filaments that connect laterals of alternate segments, in contrast to absent cortication or of loose rhizoidal filaments not connecting laterals in Pleonosporium; (ii) development of the procarp on the second to fifth cell below the apex of the female fertile filament in Compsothamnionella, in contrast to Pleonosporium where the procarp develops on the subapical cell only. It is concluded that the tribal position of Compsothamnionella is intermediate between the Ptiloteae and the Compsothamnieae. The South African species is new to science, and the name C. sciadophila is proposed.

Effects of the sterol demethylase inhibitor, cyproconazole, on hyphal tip cells of Sclerotium rolfsii: III. Cell wall cytochemistry

Hyphae of Sclerotium rolfsii were grown on cyproconazole-amended agar at fungistatic concentrations of 0.1, 0.75, and 1.0 μg/ml, which respectively produced approximately 50, 80, and 95% inhibition of hyphal extension. Hyphal tip cells were prepared for transmission electron microscopy by cryofixation and freeze substitution methods. Cell walls of control and fungicide-treated hyphal tip cells were compared cytochemically using periodic acid-thiocarbohydrazide-silver protein, gold-conjugated lectins, and immunocytochemical staining. Cell walls of both control and fungicide-treated cells reacted positively to periodic acid-thiocarbohydrazide-silver protein staining although the patterns of staining were different. Apical walls of control cells were generally thinner than those in fungicide-treated hyphae. Two distinct cell wall layers were identified in the subapical walls of control hyphae while distinct wall layers were typically not observed in fungicide-treated hyphae. Staining characteristics of abnormal cell wall deposits were variable after periodic acid-thiocarbohydrazide-silver protein stain. In regions of mature cell wall of control hyphal tip cells, wheat germ agglutinin-binding sites were localized along the inner layer of the cell wall. In fungicide-treated hyphae, binding sites for wheat germ agglutinin occurred throughout the cell wall except in electron opaque wall inclusions. Concanavalin A-binding sites were localized along the plasma membranes of both control and cyproconazole-treated hyphae in subapical cell regions. Electron opaque inclusions in abnormal cell wall deposits had affinities for concanavalin A. Immunocytochemical localization of β-1,3 glucans occurred in mature cell walls of control and fungicide-treated cells. No β-1,3 glucans were detected in electron opaque wall inclusions of hyphae exposed to cyproconazole. Alterations in the cell wall are discussed in light of the mode of action of the fungicide and aspects of cell wall deposition.

Septation behaviour of the apical cell in Streptomyces granaticolor mycelia

AbstractThe septation behaviour of the apical hyphal cell, which solely brings about hyphal elongation, was studied using mycelia grown at different specific growth rates (μ) (chemostat and batch cultures). After cell wall staining it was found that both the apical cell (c1) and the adjacent subapical cell (c2) were generally unbranched. Thus, their length (L) could be easily determined.As the growth rate decreased, Lc1 as well as Lc2 decreased, but cells smaller than 5 μm were not observed, even at extremely slow rates of growth (μ = 0.06 h−1). The largest cells were observed in rich media, where Lc1 attained 4l μm.Since Lc2 represented the length of one of the new‐born daughter cells of c1, the distribution curves of Lc2 were used to look for regularity of septation. Especially at slow rates of growth, the curves indicated that in c1 septation did not occur randomly. By using Lc2 the interdivision time T of c1 was calculated. At fast rates of growth it was identical to the earlier determined replication time C, indicating that in mature hyphae septation was coupled to the rounds of DNA replication.Lc1 and Lc2 were used to calculate the length of c1 at birth and at the start of septation. It was found that upon septation the appearing daughter cells were differently sized. Depending on the growth rate, the apically situated daughter cell was 1.37 to 1.81 times larger than the subapical daughter (c2). Based on the functional heterogeneity of the sister cells a hypothesis was invented, which could explain the asymmetric septation pattern. It involves the existence of a period S between the determination of the septum site at median position and the actual process of septum formation. The duration of S was calculated, and its correlation to the T and C values at the corresponding growth rates was discussed. Two mechanisms could be distinguished, which were responsible for the immense increase of Lc1 at fast rates of growth.

Ultrastructure of Teliospore Ontogeny inTilletia Indica

Teliospores of Tilletia indica, the Karnal bunt fungus of wheat, arose from a fixed hymenium lining all surfaces of a cavity formed by separation of the inner and outer layers of the pericarp of the grain. Scanning and transmission electron microscopy showed that the spore originated as a swelling cut off at the tip of a sporogenous hypha by a septum. The wall of the parent sporogenous cell formed the primary wall of the spore initial. Centripetal deposition of secondary wall material against the primary wall produced: 1) a thin, uniform outer layer that fused with the primary wall to form a sheath; 2) an electron opaque exospore ornamented with spines; 3) a uniform, granular endospore; and 4) a thin partition layer of sinuous lamellae separating the exospore and endospore. The complex exospore was composed of a series of concentric fibrous bands divided into two layers. In the outer ornamented layer localized deposits of dense amorphous material cemented the fibrous bands into conical spines separated by interspinal areas of loosely arranged bands. Inside of the ornamented layer the deposits of amorphous material formed a continuous dense basal layer that merged with the broad bases of the spines. The apiculus sometimes present on mature spores represented the shriveled subapical cell of the sporogenous hypha.

Ultrastructure of Teliospore Ontogeny in Tilletia indica

Teliospores of Tilletia indica, the Karnal bunt fungus of wheat, arose from a fixed hymenium lining all surfaces of a cavity formed by separation of the inner and outer layers of the pericarp of the grain. Scanning and transmission electron microscopy showed that the spore originated as a swelling cut off at the tip of a sporogenous hypha by a septum. The wall of the parent sporogenous cell formed the primary wall of the spore initial. Centripetal deposition of secondary wall material against the primary wall produced: 1) a thin, uniform outer layer that fused with the primary wall to form a sheath; 2) an electron opaque exospore ornamented with spines; 3) a uniform, granular endospore; and 4) a thin partition layer of sinuous lamellae separating the exospore and endospore. The complex exospore was composed of a series of concentric fibrous bands divided into two layers. In the outer ornamented layer localized deposits of dense amorphous material cemented the fibrous bands into conical spines separated by interspinal areas of loosely arranged bands. Inside of the ornamented layer the deposits of amorphous material formed a continuous dense basal layer that merged with the broad bases of the spines. The apiculus sometimes present on mature spores represented the shriveled subapical cell of the sporogenous hypha.

Distribution of vimentin, cytokeratins, and desmosomal-plaque proteins in human nephroblastoma as revealed by specific antibodies: co-existence of cell groups of different degrees of epithelial differentiation

The distribution of cytokeratins, desmosomalplaque proteins (desmoplakins), and vimentin in nephroblastoma tissue was studied by immunofluorescence microscopy using specific antibodies. In undifferentiated blastema cells. desmosomes, as revealed by antibodies to desmoplakins, preceded the advent of significant amounts of cytokeratins, indicating that desmosomes are early and sensitive markers of epithelial differentiation. Cytokeratin-positive tumor cells were seen in the following distribution patterns: (1) groups of loosely arranged and scattered cells containing only scant cytokeratin fibrils surrounded by negative stroma cells; (2) focal accumulation of cytokeratin-positive cells with cytokeratin-specific cytoplasmic fibril meshwork staining; (3) rosettes of cytokeratin-positive cells without formation of distinct lumina, showing concentration of cytokeratin staining in the center; (4) tubules with distinct lumina made up of cytokeratin-positive cells, with cytokeratin staining concentrated in the subapical cell portions. In cytokeratin-positive cells, the numbers of desmoplakin-positive dots were generally increased; in well-formed tubules, enrichment of desmoplakin-positive spots, corresponding to the subapical skeletal disks, was most conspicuous. Vimentin was demonstrated in stromal areas, but also in blastema cells showing coexpression of desmosomes and vimen- tin filaments. Moreover, in certain blastema cells, an overlap of cytokeratin and vimentin immunostaining was observed. Epithelial cells of nephroblastoma tubules did not react with vimentin antibodies. Our results show that the appearance of desmosomal plaques, as demonstrated by antibodies to desmoplakins, may be a very early feature of epithelial differentiation, and they also emphasize the value of antibodies to desmoplakins in tumor cell typing and diagnosis.

New terminology for sympodial growth in the Ceramiales (Rhodophyta)

‘Sympodial branching’ is a broad term describing a form of branching that occurs widely in the plant kingdom. It is expressed in different plant groups in various ways according to the basic structure of the plant, but it generally depends upon the activity of a series of determinate branches, the lower parts of which successively form the main axis of the plant. ‘Ramisympodial branching’ and ‘cellulosympodial branching’ are proposed as terms to describe the two types of sympodial branching that occur in algae. In ramisympodial branching, development of a given axis ceases and further growth of the plant is from new branches initiated in an intercalary position. In cellulosympodial branching, the apical cell itself initiates a determinate lateral branch and the lateral cell or branch formed by the subapical cell carries on development of the thallus axis. Crouanioid red algae, and a number of other types, form characteristic ramisympodial thalli, whereas dasyaceous red algae are of the cellulosympodial type.