Fine Structure of Botrytis fabae Sardina Conidia

The fine structure of Botrytis fabae conidia was studied usinga variety of electron-microscope techniques. The spore walllacks conspicuous ornamentation and consists of microfibrilsembedded in a granular matrix. The two distinct wall layersseen in chemically fixed sections cannot be detected in cross-fracturedreplicas; the two layers are probably structurally similar.The outer surface of the plasmalemma is covered with branchedinvaginations and two kinds of particles. Three distinct typesof particles are present on the inner surface of the plasmalemma.In freeze-etched replicas nuclei, vacuoles, and other organellesalways appear smoothly rounded. Small vesicles pass throughthe plasmalemma into the cell wall. Particles approximately10 nm in diameter occur in compact rows on the cristae of cross-fracturedmitochondria: dense spherical particles, probably of calciumphosphate, are present in chemically fixed mitochondria. Prevacuolesand vesicles with membranous inclusions can be seen in bothcross-fractured replicas and chemically fixed sections. In cross-fracturedreplicas vacuoles and lipid bodies are frequently joined bystrands of endoplasmic reticulum.     

Fine Structure of Germinating Botrytis fabae Sardina Conidia

The fine structure of germinating Botrytis fabae conidia wasstudied using both chemically stained sections and freeze-etchedreplicas. Germinating conidia have fewer organelles than restingconidia, glycogen is absent, and prevacuoles have disappeared.Endoplasmic reticulum which occurs as small strands close tothe cell wall of resting conidia becomes, on germination, multiplesheets surrounding the nuclei. A cross wall is formed at thebase of the germ tube soon after germination commences. Thenew wall material which appears to be continuous with this septalwall is produced, at least partly, from a new wall layer laiddown in the centre of the old conidial wall. An apical corpuscleis present at the apex of young germ tubes. Freeze-etched preparationsshow the formation of lomasomes by the passage of vesicles throughthe plasmalemma of conidia and germ tubes. In young hyphae lomasomescontain a complex arrangement of branching tubules. Some ofthe particles on the outer plasmalemma of young hyphae are arrangedin a geometrical pattern.     

Observations on the Fine Structure of the Turtle Atrium

The general fine structure of the atrial musculature of the turtle heart is described, including; the nature of the sarcolemma; the cross-banded structure of the myofibrils; the character of the sarcoplasm, and the form and disposition of its organelles. An abundant granular component of the sarcoplasm in this species is tentatively identified as a particulate form of glycogen. The myocardium is composed of individual cells joined end to end at primitive intercalated discs, and side to side at sites of cohesion that resemble the desmosomes of epithelia. Transitional forms are found between desmosomes and intercalated discs. Both consist of a thickened area of the cell membrane with an accumulation of dense material in the subjacent cytoplasm. This dense amorphous component is often continuous with the Z substance of the myofibrils and may be of the same composition. The observations reported reemphasize the basic similarity between desmosomes and terminal bars of epithelia and intercalated discs of cardiac muscle. Numerous unmyelinated nerves are found beneath the endocardium. Some of these occupy recesses in the surface of Schwann cells; others are naked axons. No specialized nerve endings are found. Axons passing near the sarcolemma contain synaptic vesicles, and it is believed that this degree of proximity is sufficient to constitute a functioning myoneural junction.     

Electron Microscope Observations on the Fine Structure of Parietal Cells

An electron microscope study has been made of the structure of parietal cells in cats, dogs, and rats and of the cells lining the gastric glands of Bufo spinulosus. It is characteristic of all these cells to contain numerous vesicles about 0.05 to 0.3 µ in size. In the mammalian parietal cells an intracellular system of canaliculi is also observed, which is much more complex in the rat than in the cat or dog. Stimulation with histamine causes in the cat a very marked hypertrophy of the canalicular system with development of a large number of villi and a decrease in the number of vesicles. In Bufo, histamine induces the formation of a very complex system of membrane infoldings which circumscribe finger-like processes that entirely fill the glandular lumen. The cytoplasmic vesicles diminish or disappear. These experiments show that under histamine stimulation all these cells undergo a great increase in the cell membrane area. These findings provide additional circumstantial evidence that parietal cells play a role in the secretion of hydrochloric acid.     

Fine Structural Studies on the Pycnidiospores of Botryodiplodia theobromae Pat.

The structure of the pycnidiospores of B. theobromae was investigatedby a combination of light microscope, a scanning electron microscopeand a transmission electron microscope observations. As observedwith the light microscope the hyaline non-septate pycnidiosporeis highly vesiculated while the pigmented septate one exhibitslongitudinal hyaline striations. Investigations with the scanningelectron microscope showed the hyaline non-septate pycnidiosporeto be smooth-walled without any form of ornamentation. The pigmentedseptate pycnidiospore on the other hand had a rough outer surfacewith a transverse groove, which probably indicated the positionof the septum. The longitudinal striations seen on such pycnidiosporeswith the light microscope were not observed under these conditions.Observations with the transmission electron microscope showedthat the outermost layer of the hyaline pycnidiospore was smootherthan that of the pigmented one. The pigment was on the outerlayer of the double-layered wall of the pigmented pycnidiospore.The inner non-pigmented wall layer was continuous with the septum.The septum tapered gradually to a thin layer in the centre whereit was perforated by a simple pore. The observations indicatedthat the pigmented spore was multinucleate while the hyalineone was uninucleate.     

Electron Microscopic Observations on the Fine Structure of Cell Walls of Chlamydia psittaci

L-cell cultures were infected with elementary bodies (EB) of meningopneumonitis organisms. Cell walls were prepared from reticulate bodies (RB), which are the intracellular developmental forms into which EB are converted, and from EB at appropriate times after infection. When fragmented EB cell walls were shadowcast with platinum palladium alloy, about one-half of the fragments were seen to be composed of hexagonally arrayed structures on the inner side of the cell wall. When EB cell walls were negatively stained with phosphotungstic acid, they all showed this fine structural array. These macromolecular units were estimated to be about 18 nm in diameter. RB cell walls, harvested at various times after infection, were similarly stained; about 20% of RB walls at 15 hr after infection showed traces of these regular structures, but only 2% of them had the structures at 24 hr. When RB cell walls prepared from penicillin-containing culture were examined, they were observed to be similar to RB without penicillin. When EB cell walls were treated with formamide at 160 C, and then centrifuged in a 10 to 40% potassium tartrate density gradient, hexagonal particles about 20 nm in diameter were obtained as a middle band in the gradient column. These particles were not obtained from RB cell walls harvested from cultures with or without penicillin. It is concluded that the particles are macromolecular subunits located on the inner side of the EB cell walls, that the subunits probably provide the structural rigidity found in the EB, and that their synthesis is inhibited by penicillin.     

Observations on the Fine Structure of the Gastric Parietal Cell of the Rat

The structure of the rat parietal cell was examined by electron microscopy. The intercellular and intracellular canalculi are lined by microvilli which are more numerous and larger than those of other gastric cells. The numerous mitochondria have closely packed cristae and a dense matrix containing opaque particles. The cytoplasmic vacuoles typical of parietal cells are part of a network of smooth surfaced tubules and vacuoles (the endoplasmic reticulum) which is intimately associated with the mitochondria and probably connected with the lumen of the canaliculi. Only a few dense particles are found attached to the surface of these tubules. The structure of the parietal cell is compared with that of other cells whose function also is transport of inorganic ions and water. Evidence is presented supporting the hypothesis that parietal cells differentiate from a less structurally specialized cell in the neck region of the gastric gland.     

Observations on the Fine Structure of the Zoospore and Young Germling of Stigeoclonium

The paper illustrates the application of some recent technicalimprovements in thin sectioning to unusually favourable material.By means of lead-stained sections of osmic-fixed material embeddedin epon, much new information regarding the fine structure ofthe flagellar apparatus, including in particular the flagellar‘roots’ and flagellar bases, has been provided.The sinking in of the flagellar apparatus after secretion ofa cell wall has been traced in outline, together with the persistenceof parts of the flagellar bases into the two-celled germlingin a manner suggesting a centrosomal function. Other observationsinclude details of the structure and arrangement of endoplasmicreticulum in swimming cells as seen in serial sections afterboth osmic and permanganate fixation, some preliminary observationson rearrangement in position of this component in the earlystages of germination, observations on the contractile vacuolesand on the special type of ‘hairy’ vesicle associatedwith them, on the Golgi bodies in both swimming and settledcells, on the distribution of ribosomes in relation to plastids,flagellar bases, the nuclear envelope, &c., and on the contents,distribution, and possible nature of various types of vesicles,including the pigment chambers of the eye-spot, vesicular derivativesof Golgi bodies, and vesicles beneath the plasmalemma in swimmingcells from which the first components of the cell wall are believedto be liberated. This work is being continued.     

Observations on the Fine Structure of the Schizonts of Haemoproteus columbae Kruse*

SYNOPSIS. The schizonts of Haemoproteus columbae resemble the exoerythrocytic schizonts of avian Plasmodium in their fine structure. Haemoproteus infects endothelial cells and grows several hundredfold in volume, destroying the cytoplasm and nucleus of the host cell. The schizont's plasma membrane is trilamellar with a dense outer lamella. Some schizonts have micropores in their plasma membranes, but there is no evidence for ingestion thru them. Instead, numerous vesicles and channels fill the host cell cytoplasm and give its plasma membrane and periparasitic vacuolar membrane the appearance of active pinocytosis. The parasite's membrane shows no sign of pinocytosis, indicating that it probably feeds by diffusion. The growing schizont has numerous mitochondria, nuclei, and ribosome-rich cytoplasm which contains electron-lucent vacuoles and clefts. The latter appear to be artifacts of fixation.     

Fine Structure Observations of Phagotrophic Activity By Plasmodia of Physarum Polycephalum

ABSTRACT. Scanning electron microscopic observations of feeding plasmodia show three characteristic features: 1) extension of multilobed pseudopodia protruding from the leading edge of the plasmodium as it advances onto the surface of a food particle, 2) confluence of the lobes to form a sheath-like pseudopodium attached to the surface of the food particle, and 3) protrusion of small nodules with thin lamellar projections from the leading edge of the plasmodium. Sections through freeze-dried preparations of the feeding plasmodium exhibit a highly convoluted under surface in contact with loosened starch grains that appear to be released by extracellular digestion. the cytoplasm, viewed by transmission electron microscopy, contains branched, internally penetrating canals (ca. 2 μm wide) enclosing engulfed starch grains. Starch grains in the deeper part of the canals are more electron dense and appear to be digested. Micropseudopodia (70-80 nm dia.), projecting from the surface of the canals, protrude toward and into the ingested starch grains. Digestive marker enzyme (acid phosphatase) activity was detected cytochemically in food particles penetrated by micropseu-dopodia indicating a digestive role for these structures not reported previously.     

Observations on the Fine Structure of Plant Cell Walls III. The Sieve Tube Wall in Cucurbita

The sieve tube wall in Cucurbita was examined in ultra-thinsections of petioles treated in different ways for the removalof non-cellulosic wall components. The sections were stainedwith permanganate. The microfibrillar components of the wallare arranged in concentric lamellae. The earliest (outermost)part of the wall is similar to that of ordinary parenchyma inhaving its lamellae composed of thinly-distributed microfibrilsreadily separated from one another by certain treatments suchas pectinase extraction. In the characteristically-thickenedinner (nacreous) layer the microfibrils are very densely packedand the lamellae do not separate readily. The microfibrils inthis layer of the wall are very close to transverse and the‘crossed fibrillar’ orientation is not easily discernible.     

Observations on the Fine Structure of the "Cyst Stage" of Besnoitia jellisoni

SYNOPSIS. Light and electron microscope studies of the "cyst" of Besnoitia jellisoni indicate that it consists of an extracellular wall, a large, sometimes multinucleate, host cell, and an intracellular vacuole containing the parasites. The "cyst" wall has fine fibrils and small dense granules embedded in an election-lucid matrix. The wall may be formed from a secretion of the enclosed host cell. The plasma membrane of the host cell is very irregular, being modified into microvillar or pseudopodial extensions. Small vesicles and invaginations of the plasma membrane indicate mioropinocytosis. The one to several large lobular nuclei lie in a thick area of cytoplasm which is filled with rough endoplasmic reticulum and many mitochondria with lamellar cristae. The parasite-containing vacuole is limited by a vacuolar membrane which has many blebs suggesting a transfer of materials into the vacuole.
The "cyst" organisms are crescentic or piriform and are enclosed by a pellicle consisting of outer and inner membranes. Twenty-two subpellicular fibrils extend longitudinally adjacent to the inner membrane from the anterior polar ring to a posterior ring. A micropyle is situated laterally in the pelliole near the level of the nucleus. A conold and several associated paired organelles are present at the anterior end. Microuemes, more abundant in older organisms, are also present in the anterior portion of the parasite. A Golgi apparatus lies adjacent and anterior to the nucleus. One or more mitochondria with saccular cristae, ovoid glycogen bodies, free ribosomes and occasional vacuoles are also present. Organisms within the "cyst" multiply by endodyogeny.     

Observations on the Development and Fine Structure of the Articulated Laticifers of Papaver somniferum

The development and fine structure of articulated anastomosinglaticifers in Papaver somniferum were studied. Laticifers arenot present in the embryos but differentiate soon after germinationand are found in the phloem areas 18–30 h after the seedis sown. Laticifers and sieve elements are generally separatedby at least one cell layer in the roots, but in cotyledons,stems, and leaves they usually occur adjacent to each other. As the laticifers differentiate an abundance of vesicles formsin the cytoplasm. This process appears to involve the endoplasmicreticulum and it is suggested that the vesicles may be a specializedform of vacuole. Substances present in the vesicles react stronglywith iodine-potassium iodide. Laticifer-cytoplasm persists peripherallyand between the vesicles. It contains the usual cell organelles,the presence of which substantiates an active metabolic rolefor the laticifer contents.     

Observations on the Fine Structure of the Zoospore of Oedogonium cardiacum with Special Reference to the Flagellar Apparatus

Parts of the flagellar apparatus both inside and outside thecell have been investigated in a preliminary way by sectionsand whole mounts. Zoospores from male plants of O. cardiacumpossess about 120 flagella, the bases of which are held togetherin a ring by means of a characteristically patterned fibrousband and some differently arranged more homogeneous material.Between each pair of bases a compound root passes backwardsinto the cell. Each root has two radially superposed components:the outer component consists of three fibres starting at thefibrous ring and passing backwards close to the cell surface;the inner component is shorter and stouter, extending backwardsfor an uncertain distance but penetrating forward below thefibrous ring, to end within the substance of the colourlessapical dome of the cell. The material of the inner componentof a root displays a regular crossbanding of alternate thinand thicker lines spaced at approximately 140A for each unitof pattern (i.e. two lines). The orientation of the free partsof the flagella with respect to the fibrous ring is such thattheir two central strands when seen in cross-section near thebase are obliquely vertical.     

Observations on the Fine Structure of Plant Cell Walls: I. Use of Permanganate Staining

Aqueous solutions of potassium and barium permanganates usedas post-stains for ultra thin sections are effective in revealingthe microfibrillar framework of parenchymatous walls when thetissues are extracted, prior to embedding, with macerating andclearing agents for non-cellulosic wall components. Images ofthe collenchymatous wall in permanganate-stained sections ofCucurbita petioles treated variously with pectinase, protease,H₂O₂-acetic acid and NaOH are presented.