Martha J. Powell

The role of kinetosome-associated organelles in the attachment of encysting secondary zoospores ofSaprolegnia ferax to substrates

SummaryElectron and fluorescence microscopy were used to identify organelles involved in attachment of secondary zoospores ofSaprolegnia ferax as they were transformed into secondary cysts. When secondary zoospores were exposed to 1.0% peptone in the absence or presence of a substrate, they began to encyst. If substrates were present when encystment was induced, the groove surface of the secondary zoospores adhered to them. The first event in attachment was secretion of contents of the kinetosome-associated organelle (K-body), which was typically oriented with the tubule-filled cavity positioned toward the cell surface of the groove region in the zoospore. The tubules which contained carbohydrates became coarsely granular, the matrix became more fibrous, and the shell remained along the membrane concavity that was formed as the K-body fused with the plasma membrane.Five minutes later, a cyst coat appeared, and cysts were not readily dislodged from a substrate. The concavity was no longer found, presumably because it had evaginated; but a layered pad of adhesion material was between the cyst coat and substrate. The layers of the adhesion pad corresponded to the structure of the matrix of K-bodies. As with the tubules of the K-body, the coarsely granular portion at the edge of the pad stained for carbohydrates. Similarly, the lectins WGA and GS-II labeled with fluorescein stained the rim of the adhesion pad on cysts, indicating the presence of glycoconjugates containing N-acetylglucosamines. Because globular areas near the kinetosomes and groove of zoospores (where K-bodies were located) also bound WGA and GS-II, K-bodies contained the same carbohydrates as the adhesion pad. We conclude that K-bodies function in the attachment of encysting zoospores to substrates as the cell differentiates. The tubular portion of the K-body matrix contains carbohydrates which might assist in the adhesion process.

Fine structure of the unwalled thallus of Rozella polyphagi in its host Polyphagus euglenae

The endoparasitic chytrid, Rozella polyphagi, was found infecting another chytrid, Polyphagus euglenae, which is itself an epiparasite ofEuglena viridis and E. gracilis. An electron microscopic study revealed the unwalled, multinucleate thallus of the endoparasite in prosporangia and sporangia of P. euglenae where the plasma membrane of the endoparasitic thallus was in direct contact with the cytoplasm of P. euglenae. Profiles of degenerating host mitochondria in vacuoles of the endoparasite and of cytoplasmic projections of the endo? parasite around portions of host cytoplasm suggest that the endoparasite phagocytizes host protoplasm. A discussion of interfaces between unwalled endoparasites and their hosts show that the absence of host enveloping membranes around endoparasites and the capability of endoparasites to phagocytize host cytoplasm is more common than generally recognized.

Terminology and nomenclature of protist cell surface structures

SummaryThe use of a precise terminology is important to the unambiguous exchange of information in the multidisciplinary area of protistology. In this paper we attempt to establish clear definitions, give illustrations, and comment on the different terms used for cell surface structures of protists and related organisms.

Microbody-like organelles as taxonomic markers among Oomycetes.

Zoospores of Oomycetes contain a variety of microbody-like organelles with highly structured matrices. Although in general their function is unknown, the appearance of similar organelles in related taxa suggests the ultrastructural differences could be used as taxonomic characters. This study surveys microbody-like organelles of oomycetous zoospores to determine if this is an additional criterion by which the phylogeny of these fungi can be evaluated. In zoospores of the order Saprolegniales, kinetosome-associated organelles (K-bodies) are found which typically consist of tubular and/or granular matrices. K-bodies are not found associated with kinetosomes in zoospores of the Peronosporales, but microbodies containing tubules, and in some genera marginal plates, are located near the kinetosomes, along the groove, and in other peripheral areas. K-bodies have been reported in only one member of the order Lagenidiales. These K-bodies lack a granular matrix, but contain a single curved plate from which tubules arise, forming a cone. In the one genus of the Leptomitales examined, a similar K-body contains a plate and scattered tubules. Organisms with similar microbody-like organelles are probably more closely related than those with different types of microbody-like organelles. The presence of an organelle resembling K-bodies in zoospores of an alga in the Tribophyceae supports the phylogenetic association between algae and Oomycetes. A complete survey of Oomycete genera may well reveal intermediates between the structurally different types of microbody-like organelles, allowing the reconstruction of the phylogenetic history of an organelle.

Zoospore fine structure of the parasite Olpidiopsis saprolegniae variety saprolegniae (Oomycetes, Lagenidiales)

ABSTRACTZoospore fine structure of Olpidiopsis saprolegniae var. saprolegniae was analyzed with light and transmission electron microscopy and was compared with that of other Oomycetes studied prev...

Cytochemical Detection of Polysaccharides and the Ultrastructure of the Cell Coat of Zoospores of Chytriomyces Aureus and Chytriomyces Hyalinus

The formation and structure of cell coats on zo6spores of Chytriomyces aureus and C. hyalinus are described from an ultrastructural and cytochemical study. After zoospore initials are cleaved, but before organelles are organized into the arrangement found in free-swimming zoospores, dictyosomal vesicles deposit a cell coat on the outer surface of the plasma membrane. In free-swimming zoospores, the cell coat covers all of the zoospore except the flagellar sheath. The inner layer of the cell coat is homogeneously dense and is covered with an outer layer of helically arranged spines. Both layers of the cell coat stain with the silver methenamine technique for polysaccharides, as do glycogen and fibril-containing vesicles in the cytoplasm. Sodium bisulfite and hydrogen peroxide controls confirm the polysaccharide specificity of the reaction in glycogen deposits, vesicles, and the outer layer of the cell coat. Use of the sulfhydryl blocking agent, iodoacetate, demonstrates sulfhydryl-containing compounds in the inner layer of the cell coat.

Production and modifications of extracellular structures during development of chytridiomycetes

In development of the primitive fungi, chytridiomycetes, unwalled zoospores bearing single, posterior flagella are transformed into walled, round-cells which elaborate the thallus. Production, structural modification, or release of extracellular material are involved with each transition of developmental stage. This article reviews the variety and developmental changes of extracellular materials found at the cell surface of chytridiomycetes. A cell coat, produced from Golgi-derived vesicles during zoosporogenesis, is visible around free swimming zoospores of some chytridiomycetes. How the zoospore surface receives and transduces signals is not widely explored, but it is known that fenestrated cisternae and simple cisternae, which are integrated into the microbody-lipid globule complex, are spatially and structurally associated with the plasma membrane and flagellar apparatus. This spatial association, as well as the cytochemical localization of calcium in fenestrated cisternae, suggest a mechanism for signal transduction and for regulation of zoospore motility. Zoospores become encased in a new layer of extracellular material as the zoospore encysts. Among some chytrids the source of this material is preexisting vesicles which fuse with the plasma membrane. Among other zoospores, a readily identifiable population of encystment vesicles is not apparent, demonstrating that there is no single pattern or mechanism for zoospore encystment in chytridiomycetes. Encysted zoospores developing into thalli, typically produce cell walls with a microfibrillar substructure. Ultrastructural analysis of walls reveals distinctive architecture and remarkable sculpturing which have been used in systematics of some members of chytridiomycetes. Nothing is known as to underlying controls of cytoskeletal elements and plasma membrane enzyme complexes in wall biogenesis. Many changes in cell surface structures accompany thallus maturation. Septa, many traversed with plasmodesmata, are produced in most chytrid thallus types. As sporangia and resting spores prepare for the production and release of zoospores, additional extracellular layers of material are frequently produced. Polarized deposits of extracellular material become discharge plugs, discharge vesicles, or endoopercula. Interstitial material is also released into cleavage furrows. Circumscissile or localized digestion of walls produce operculate or inoperculate exit ports for zoospore release. Cryofixation preserves more extensive extracellular material than does conventional chemical fixation, and broader application of cryofixation may radically alter our current view of cell surface structure. Thus chytridiomycetes exhibit a range in patterns for the occurrence and subsequent modifications of extracellular materials, even for members within the same order. The most universally recognized role for these extracellular materials is protection. Although there is a reasonable view of the types of extracellular material involved in chytridiomycete development, we have only limited understandings of their biogenesis or roles in regulation and communication, areas awaiting more investigations.

Cross-linking bridges associated with the microbody-lipid globule complex inChytriomyces aureus andChytriomyces hyalinus

SummaryDetermining how the orientation and association among organelles are maintained within zoospores of theChytridiales is important to understanding the control of zoospore motility. Zoospores of the aquatic fungi,Chytriomyces aureus andC. hyalinus, contain microbody-lipid globule complexes with an elongate microbody adjacent to the portion of a lipid globule facing the cells interior and a fenestrated cisterna (the rumposome) opposed to the surface of the lipid globule toward the plasma membrane. Mitochondria are intimately associated with the microbody. Electron microscopy of the microbody-lipid globule complex fixed in glutaraldehyde and osmium tetroxide, with or without tannic acid, reveals cross-linking bridges connecting the rumposome to the plasma membrane, to the microbody, and to microtubules of the rootlet extending from the kinetosome. It is concluded that these bridges are responsible, at least in part, for the consistent location of the microbody-lipid globule complex in the zoospore body. The possible role of the rumposome as a receptor organelle is discussed.

The structure of microbodies and their associations with other organelles in zoosporangia ofEntophlyctis variabilis

SummaryThe ultrastructure of microbodies in developing zoosporangia ofEntophlyctis variabilis was studied by three dimensional reconstructions from serial sections and by cytochemical localization of catalase activity. The morphology of microbodies and the spatial association of microbodies with other organelles varied during fungal development. In incipient zoo-sporangia, granular dilations resembling microbodies arose from rough ER. Young, enlarging zoosporangia contained elongate, contorted microbodies continuous with ER and aligned along bundles of microtubules. Oval, paired microbodies, lying on each side of an ER cisternae, were found in all zoosporangia, but in older zoosporangia this configuration of microbodies predominated. Analysis of serial sections revealed that these oval, paired microbodies were sometimes continuous with each other, with ER, and also apparently with the ER cisterna interposed between them. Other paired, oval microbodies were clearly discrete. Constrictions were found along the length of elongate microbodies and at junctions between oval microbodies. These constrictions may represent stages in fragmentation of microbodies from pre-existing microbodies. These observations suggest that microbodies originated in three ways: 1. as local dilations in tubular ER, 2. as lateral buds from opposite sides of ER cisternae, and 3. as fragments from elongate microbodies.Microbodies were consistently spatially associated with ER, nuclear envelopes, and mitochondria. The cisterna of ER passing between paired microbodies sometimes extended into a branching, tubular system of ER which curved around the side of one microbody and lay between this microbody and the forming face of a dictyosome. The cytochemical localization of thiamine pyrophosphatase activity in this cisterna when it is not associated with dictyosomes suggests a role in metabolic control. These spatial associations indicate that the microbody assemblage with other organelles represents functional units where propinquity to other organelles and intraluminal continuities insure a system for transport of substrates and products.

Cytochemical localization of carbohydrates in zoospores of Saprolegnia ferax

The subcellular location of carbohydrates in secondary zoospores of Saprolegniaferax was determined from an electron cytochemical study. Specificity of reactions was verified with the sulfhydryl blocker iodoacetate, and the dialdehyde blocker dimedone. Although no cell coat was visible on the zoospore surface, the plasma membrane and the flagellar sheath contained an abundance of carbohydrate and sulfhydryl compounds. Deposition of reaction product and results of controls demonstrated that similar compounds were also on membranes of the water expulsion vacuole system. Peripheral vesicles contained reaction product over their fibrous contents, demonstrating the presence of carbohydrates, and controls indicated that sulfhydryl groups were most likely also present. Sulfhydryl-containing carbohydrates and other carbohydrates were compartmentalized in the tubule-filled cavity of kinetosomeassociated organelles (K2 bodies), while their granular matrix was unreactive. Vital roles of carbohydrates in oomycetous zoospores are incompletely understood, but this study suggests mechanisms through which they may function in the stability and recognition of membranes. This is the first report of carbohydrates in K2 bodies and provides a basis to explore the function of this novel organelle.