Fine Structure of Quiescent and Germinating Aeciospores of Cronartium fusiforme

Aeciospores of the long-cycle heteroecious rust fungus, Cronartium fusiforme, were found to have an extremely thick cell wall with striking spicules protruding from it. The wall was readily degraded by commercial chitinase, but spicules were unaffected. Quiescent spores contained two nuclei with distinct nuclear membranes possessing many pores. Numerous membrane-bounded lipid bodies were found both in wild-type orange and in white mutant aeciospores. An abundance of irregularly ovoid mitochondria was present in quiescent spores. After glutaraldehydeosmium fixation, the surface of the mitochondria appeared to be covered with ribosomes or microtubules in a paracrystalline array, whereas after permanganate fixation only smooth outer mitochondrial membranes were noted. The latter fixative revealed abundant vesicular endoplasmic reticulum in the spore. Spores incubated at 20 C on agar produced one to five distinct germ tubes within 65 to 180 min. These thin-walled tubes exhibited varying degrees of branching, and reached a total hyphal length of 300 to 500 mu prior to rupturing. Emergence of germ tubes took place through a pore in the spore wall and appeared to be mainly a physical flowing of cytoplasm from the spore into the germ tube without division of nuclei or other cell organelles. On completion of germination, the protoplasm of the germ tube contained both nuclei and nearly all of the other spore contents. Mitochondria had smooth outer membranes, were greatly elongated, and possessed distinct longitudinal cristae. A limited amount of rough endoplasmic reticulum was arranged parallel to the germ tube wall. Other organelles seen in germ tubes were lipid bodies, concentric membrane figures, and numerous ribosomes. Lipid bodies appeared smaller and fewer in number than in quiescent spores.     

The Fine Structure of Quiescent and Growing Carrot Cells: Its Relation to Growth Induction

This paper records a survey of the fine structure of carrotcells. Cells have been examined in the state in which they occurin the dormant root, and under the influence of stimuli whichcause them to grow and divide rapidly. Although the carrot cells,which are often highly vacuolate with very thin parietal cytoplasm,presented special technical difficulties, these were overcome.The information which has been obtained has special significancebecause it can be related to cells that undergo a recrudescenceof growth brought about by known agents and conditions. Theinduction of growth in otherwise resting tissue is manifestat all levels from protoplasmic streaming, the position anddivision of nuclei, the abundance of cytoplasmic strands, allseen under the light microscope, as well as effects which areonly visible with the electron microscope on the ground substanceof cytoplasm and upon all the organelles that have been investigated.By deliberate choice a variety of techniques have been employed;some of these emphasize the membrane components of the cytoplasmand its organelles, others stress their granular non-membranouscontent. In this way sharply contrasting pictures of plastidsand mitochondria are obtained. Some methods show the cell wallwith its cellulosic fibrils conventionally revealed; othersdemonstrate it in the form of non-cellulosic droplets or granulesobviously mounted upon very fine supporting threads. By allthese means the quiescent and actively growing cells are contrastedwith reference to each of their prominent features. Ribosomes,both free and attached to membranes, are conspicuously abundantin the activated cells and this correlates with the known relationof the nucleic acid metabolism to their growth and protein synthesis.The endoplasmic reticulum, mitochondria, plastids, Golgi bodies,are all conspicuous in the activated cells which can divideand there are characteristic differences in their form and structurewhich can be seen during growth induction. The new cell wallat cytokinesis (middle lamella) has been seen as well as theformation of protoplasmic connexions, which unite the derivativesof one cell into an organized structure. The later events thatoccure in the formation of an air space, which permit valuableobservations on cell walls to be made, have also been described.Thus the electron microscope is now a valuable tool to supplementstudies on the biochemical effects of growth-regulating substancesand in the understanding of growth induction; aseptically culturedtissue explants and free cells, used under conditions in whichgrowth and morphogenesis may occur, constitute equally valuablematerial for the investigation of the fine structure of cellsand its relation to development.     

The Quiescent Centre and Cell Determination in Roots of Pisum sativum

A combined autoradiographic and enzyme cytochemical study ofroot apices from Pisum sativum has permitted the demonstrationof a high naphthol AS-D esterase activity in the central groupof meristematic cells immediately outside the quiescent centre.This high naphthol AS-D esterase activity indicates an expressionof the programming of these cells to form elements of the stele.A consideration is given to the need for a quantal mitosis andof its possible occurrence in the quiescent centre. It is concludedthat the programming and mitotic activity may be two physiologicalevents which whilst occurring in the same cell, are not necessarilylinked events. Pisum sativum, roots, determination, quiescent centre, autoradiography, carboxylesterases     

The Fine Structure of Plastids in Various Tissues in the Leaf Blade of Rice

Ultrastructural variations of plastids in a leaf blade of riceare examined by electron microscopy. Plastids are identifiedby their starch-accumulating activity in detached leaves illuminatedfor 48 h. Plastids are observed in all the tissues that containcytoplasm. The structure of plastids varies among differenttissues but is rather uniform within a tissue. Among varioustypes of plastids other than chloroplasts in chloren-chyma,plastids of guard cells, sieve elements, and companion cellsare characteristic of the respective tissues. Ultrastructuralfeatures of vascular bundles and stomata of the leaf blade ofrice are also described.     

Fine Structure of the Hemopoietic Tissues in the Mealworm Beetle, Tenebrio molitor

The fine structure of the hemopoietic tissue and its detailed reticular organization in the mealworm beetle, T. molitor were examined using light and scanning electron microscopes. The major hemopoietic tissues in the abdomen were located on the upper surface of the dorsal diaphragm which continuous over the ventral wall of the heart. Histologic characteristics of this hemopoietic tissues are dense clusters of cells. They are irregular in outline and are not surrounded by any connective tissue sheath. The hemopoietic tissue of this insect is consisted of three cellular components which are the reticular cells, hemocytic stem cells and several kinds of mature hemocytes. The reticular cells had numerous cytoplasmic processes and forming a complex network. The stem cells give rise to differentiating hemocytes of the different cell lineages. Mature hemocytes within this hemopoietic tissue are originated from the stem cells and differentiated into several types of hemocytes including prohemocytes, plasmatocytes, and granulocytes.     

Fine Structure of Rickettsia canada in Tissues of Dermacentor andersoni Stiles

Preliminary observations on growth and developmental fine structure of Rickettsia canada in various organs and tissues of the hard tick, Dermacentor andersoni Stiles, are reported. R. canada is typically rod-shaped, being delimited with a three-layered wall having a velvety coating adsorbed to its exterior surface. A finely reticulated cytoplasmic matrix containing prominent ribosomes is delimited with a three-layered unit membrane. Average length and width of these organisms are 1.6 by 0.4 mum. Although R. canada produces a generalized infection in D. andersoni, hypodermal and muscle tissues experience heaviest growth. Three morphologically distinct rickettsial forms were observed in individual hypodermal cells: (i) typical growth forms with a finely reticulated cytoplasmic matrix and distinct ribosomes; (ii) atypical forms with lightly to densely staining cytoplasm and a coagulated appearance in which ribosomes cannot be distinguished from the matrix; and (iii) forms with crystalline bodies that have a striated to beaded lattice structure and, at times, a fibrillar body in the cytoplasm as well. Occasional finger-like to irregular invaginations of the plasma membrane are noted. Intranuclear growth was demonstrated by electron microscopy in gut epithelial cells only. Growth and development of R. canada were manifest in all tissues examined.     

The Fine Structure of some Dry Seed Tissues Observed after Completely Anhydrous Chemical Fixation

Completely anhydrous fixation with acrolein vapour or osmiumtetroxide vapour was applied to tissues of air-dry seeds: thecoleoptile of wheat (Trilicum aestivum), and plumule and radicleof mung bean (Vigna radiata). Great shrinkage of cells and organelleswas noted, but all the usual organelles could be identified,except for Golgi bodies and (in most cases) ribosomes. The endoplasmicreticulum was very abundant and endoplasmic reticulum tubuleswere closely associated with the storage organelles, namelylipid bodies in the wheat coleoptile, and protein bodies inthe mung bean embryo axis. Aqueous fixation resulted in considerabledistortion of cellular structure. Triticum aestivum L., wheat, Vigna radiata L., mung bean, seed, fine structure, anhydrous fixation     

Nuclear Chromatin Structure in Relation to Cell Differentiation and Cell Activation in the Cap and Quiescent Centre of Zea mays L.

Barlow, P. W. 1985. Nuclear chromatin structure in relationto cell differentiation and cell activation in the cap and quiescentcentre of Zea mays L —J. exp. Bot. 36: 1492–1503.Nuclear chromatin structure has been analysed by electron microscopyof thin sections of cells in four zones of the root cap—meristem,central, slime-secreting and outermost cells—and alsoin the quiescent centre of the root before and after decapping.The chromatin pattern has been related to the DNA and RNA syntheticactivity of the nuclei. During cap cell maturation there wasa progressive condensation of the chromatin and this was accompaniedby some reduction of RNA synthesis. The degree of condensationwas estimated from the area and number of pieces of electrondense chromatin which increased and decreased, respectively,during cap maturation. The volume fraction of condensed chromatinwas also estimated but, in the cap, was not found to be a goodindicator of nuclear activity. The outermost cells of the capshowed the greatest degree of chromatin condensation but werestill active in RNA synthesis. Microdensitometry of their nuclearDNA contents gave an indication of loss of DNA in some of thenuclei. Decapping activated DNA and RNA synthesis in the quiescentcentre and also stimulated a decondensation of chromatin: thenumber of condensed pieces of chromatin increased, and theirsize and volume fraction both decreased 4 h after decapping.The number of pores per unit length of nuclear envelope profilewas also estimated. In the cap this number increased duringcap maturation; in the activated quiescent centre the numberremained constant except for a small rise 4 h after decapping Key words: Zea mays, chromatin, root cap, quiescent centre     

The Meristem and Quiescent Centre in Cultured Root Apices of the gib-l Mutant of Tomato (Lycopersicon esculentum Mill.)

Cultured root apices of tomato bearing the gib-I mutation, whichreduces the levels of endogenous gibberellins, grew slower andwere thicker than wild-type contols. This was the result ofshorter and broader cells in the menstem of the mutant. Cellsof both cortex and stele were affected, but this did not causeany alteration to the volume fraction occupied by these twotissues in the root meristem. Root caps were longer in the mutantand there were also more layers of rhizodermis. All these effectscould be reproduced in wild-type roots by addition of 0.1µM2S, 3S paclobutrazol (an inhibitor of gibberellin biosynthesis)to the culture medium and could be normalized in mutant rootsby 0.1 µM GA₃. Cell doubling times in the proximal regionof the meristem were similar in mutant and wild-type roots,but were faster in both the quiescent centre (QC) and the capmeristem of the mutant. This latter feature of the mutant rootsis likely to be the cause of their longer caps, while the fasterrate of division in the QC accounts for the additional tiersof cells that were found to build up in the cortical portionof this zone These additional tiers failed to form in mutantroots grown in GA₃, but they could be induced in wild-type rootsby 2S, 3S paclobutrazol. These results suggest that endogenousgibberellins may be partly responsible for the slow rate ofcell growth and proliferation in the QC. Gibberellins, gib-I mutation, Lycopersicon esculentum, meristem, roots, 2S, 3S paclobutrazol, quiescent centre, tomato     

The Fine Structure of Avocado Plastids

Ultrastructural studies of both young and harvest-ripe avocadofruits have established that the skin and outer green layersof flesh contain chloroplasts with an extensive thylakoid system.Etioplasts occur in the yellow flesh adjacent to the stone.The pale-green flesh contains plastids, intermediate betweenchloroplasts and etioplasts, which have prominent prolamellarbodies from which radiate grana. When segments of both the yellow and pale-green flesh of maturefruit (7 cm diam.) are cultured in the light their prolamellarbodies do not disperse although there is a change in their crystallinity.The palegreen tissues of immature (4 mm and 2 cm diam.) fruitsalso contain etioplasts but on culturing these differentiateinto chloroplasts. Both chlorophyll content and the ratio ofchlorophyll a to b varied in the different tissues of youngand mature fruits.     

The Fine Structure of the Slimeways in Labyrinthula

SYNOPSIS. Electron microscope observations of a strain of Labyrinthula indicate that the spindle cells glide within a collapsible slime tube rather than on top of it. These slimeways are clearly extracellular, partly covered with membranes, and consist of an amorphous matrix encrusted with many small vesicular elements.     

Fine Structure Analysis of the ade3 Locus in SACCHAROMYCES CEREVISIAE

Twenty-six spontaneous mutants at the ade3 locus of Saccharomyces cerevisiae have been mapped and characterized with respect to revertibility, osmotic remediability and temperature sensitivity. Twelve of the twenty-six are temperature sensitive, 25 of 26 are osmotic remedial and 21 of 26 revert. Two of the mutants map as deletions. At least five of the 26 are nonsense mutations but are also, unexpectedly, osmotic remedial. Three nonsense mutations are also temperature sensitive, again an unexpected result. The two multisite mutations are both temperature sensitive and osmotic remedial. For mutants at this locus osmotic remediability and temperature sensitivity cannot be considered diagnostic criteria for missense mutations.     

The Fine Structure of the Sporozoite of Lankesteria culicis

SYNOPSIS. The sporozoite of Lankesteria culicis was studied by light and electron microscopy, after excystation in the intestine of Aedes aegypti 1st stage larvae. The sporozoite was 9.5–10.0 μ long with a blunt anterior end and a tapered posterior region. The organism was enclosed by a typical pellicle consisting of an outer and an inner membrane with underlying subpellicular microtubules. The anterior end had a conoid with 2 associated rings, a polar ring which served as a termination of the subpellicular microtubules and a flask-shaped structure situated internal and posterior to the conoid. A micropyle consisting of a collar formed from the inner membrane and lacking an invagination of the outer membrane was present near the anterior end of the parasite. The nucleus was centrally located and had a peripheral concentration of chromatin and a central nucleolus. One or more mitochondria were observed in the vicinity of the nucleus.     

The Fine Structure of Some Retinal Photoreceptors

An electron microscope study has been made of octopus and amphibian photoreceptors, after fixing with KMnO₄ and embedding in araldite. What has previously been seen as a single dense stratum bounding the tubular compartments (octopus) or the double membrane discs (rods and cones), now shows a double structure. We interpret this as showing that these tubules and discs have similar bounding surfaces, which are probably directly related to the cell membrane. This is confirmed by the finding that the tubules and discs are (at least occasionally) continuous with the cell membrane.     

The Fine Structure of the Developing Euphorbia dulcis Endosperm

Euphorbia dulcis has a nuclear type of endosperm which laterbecomes cellular. During the coenocytic period, the Golgi apparatusconsists of moderately proliferating dictyosomes. The endoplasmicreticulum is large, rough and manifests as long cisternal profileswhich are scattered singly or packed in parallel multiple arrays.The mitochondria exhibit different numbers of small cristaeand frequent outline constrictions suggesting approaching binaryfission. The plastids have only slightly structured stromataand contain little or no starch; like the mitochondria, manyof them have indented profiles. Wall formation is seen as chain-like aggregates of coalescingdictyosome vesicles with much associated endoplasmic reticulum.The latter is discussed in terms of cisternal shape, generalthree-dimensional form and probable involvement in trappingGolgi derivatives. The newly constituted cells are highly vacuolateelements having large populations of free ribosomes, many immatureplastids and relatively more numerous mitochondria. Opaque (lipid)bodies are found in the neighbourhood of the plasmalemma. Theendoplasmic reticulum is granular. The presence of a micropylar network of labyrinthine ingrowthsstudding the boundary wall of the coenocytic endosperm is alsodescribed. Euphorbia dulcis, endosperm, ultrastructure, wall ingrowths     

A Genetic Fine Structure Analysis of the Suppressor 3 Locus in Saccharomyces

A meiotic fine structure map of a yeast tyrosine-inserting ochre suppressor, SUP3-omicron, was constructed. This was accomplished by examining ten intragenic suppressor-inactive revertants for their relationship to each other and to the original SUP3-omicron mutation. The second-site revertants map on both sides of the SUP3-omicron mutation. The meiotic map length based on the summation of short intervals is 45+/10(5) asci.     

The Fine Structure of the Gametocytes of an Adeleine Haemogregarine

SYNOPSIS. Gametocytes of an unidentified haemogregarine (Sporozoa, Telosporea, Coccidia, Eucoccida, Adeleina, Haemogregarinicae) from the frog Rana montezumae were examined by light and electron microscopy. The fully-grown gametocytes lay in a vacuole in the erythrocyte, surrounded by a sheath which was probably of parasitic origin. The gametocytes were bounded by a pellicle of 2 unit membranes, beneath which lay a ring of small longitudinal fibrils. At the anterior end there were 2 concentric layers of larger longitudinal fibrils, arranged in a truncated cone, lying between the pellicle and the cytoplasm of the parasite. The cytoplasm contained a few small mitochondria, many inclusions resembling lysosomes, and small vacuoles; there were also 2 larger, anterior inclusions, which did not appear to run to the tip of the organism. Numerous ribosomes were seen, but no endoplasmic reticulum. The single nucleus contained discrete, dense, granular masses, perhaps deoxyribonucleoprotein, and was apparently limited by only a single membrane.