Tapetal Organization During Sporogenesis in Psilotum nudum

Stages in the differentiation of the tapetum of Psilotum nudumare described. Two concurrently occurring components of thetapetum can be recognized. A plasmodial tapetum with associatedfunctional nuclei develops within the sporangial loculus duringthe early stages of differentiation, appears to remain viablefor several months, that is during the entire period of sporogenesis,and undergoes reorganization on three occasions. During MeiosisI groups of spore mother cells are enclosed in clear areas withinthe plasmodium: by the end of Meiosis II each tetrad is isolatedin a plasmodial chamber; and, finally, mature spores are enclosedwithin individual tapetal chambers. Typically enlarged cellsare present during the development of a cellular, parietal tapetum.A sporopollenin-containing layer or tapetal membrane characteristicof a secretory tapetum develops on the inner tangential walland lines the surface of the loculus. This tapetal membranepersists even after dehiscence of the sporangium. These observationsare discussed in relation to previously published conflictingdata and may be relevant to the arguments concerning the relationshipof the Psilotaceae to the Filicales. Psilotum nudum, light microscopy, parietal tapetum, plasmodial tapetum, tapetal membrane, tapetal reorganization, sporogenesis, sporopollenin     

Autotropism in Fungal Spores

Autotropism was examined in germinating spore pairs of Rhizopusstolonifer, Mucor plumbeus, Trichoderma viride, and Botrytiscinerea. When germinated on agar surfaces the first three speciesexhibited negative autotropism, B. cinerea being neutral inits autotropic behaviour. More pronounced negative autotropismwas shown by the first three species when germinated on a filmof Cellophane applied to an agar surface. Under these conditionsB. cinerea displayed positive autotropism. Spore pairs of R. stolonifer germinated on agar containing cellulosepowder or charcoal showed less negative autotropism than onagar alone. Touching spore pairs of each species showed a markedtendency towards cis-ness, i.e. germ-tubes beginning on thesame side of a line joining the two spore centres, under theculture conditions described, the one exception being the reductionin cis-ness recorded when R. stolonifer was germinated on agarcontaining charcoal. Time courses of germination were determined for single sporesand touching spore pairs of R. stolonifer and M. plumbeus anda significant promotion was obtained in the spore pairs as comparedwith the single spores. Although both these species exhibitmarked negative autotropism there was a strong tendency forthe positive germ-tube, i.e. one beginning more nearly towardsits neighbour, to emerge before the negative germ-tube in thosespore pairs having one germtube positive and the other negativein orientation. Also, in R. stolonifer, the replacement of germination-promotersby germination-inhibitors in filtrates from spore suspensionsas they age is correlated with a change from positive to negativeautotropism in germinating members of (+ –) spore pairs. Possible mechanisms are discussed to account for the observedeffects.     

Observations on the Internal Structure of the Spermatozoid of Dictyota

The spermatozoid of Dictyota is shown to be structurally morelike a vegetative zoospore than was the case in Fucus. The mitochondria,golgi, overall shape of the nucleus, nuclear membrane, fat bodies,and miscellaneous vesicles are as in a zoospore; there is, however,a vestigial chromatophore without an eyespot and the ciliaryapparatus is specialized. In spite of the single flagellum thereare two basal bodies inside the cell, one of which is apparentlyvestigial, ending blindy in the cytoplasm; both the a similarinternal structure with nine fibres in the wall. A fibrous ‘root’,possibly homologous with the ‘proboscis’ of Fucus,arises near the outer side of the functional basal body; itis a band of about eight fibres passing through the cell withouttouching the nucleus but closely pressed to the inner facesof at least two mitochondria before ending in an unknown mannerat the cell surface. The internal structure of the flagellumis normal but the fact that the median strand is marked by arowspines has been used to demonstrate is a conclusive way thefacts of bilateral symmetry in the whole organ; Dictyota agreesexactly with Fucus and a previous error based on incompleteinformation has been corrected. The process of unwinding ofthe flagellum from the surface of the body after liberationfrom the antheridium is described and used to illustrate someunexpected properties of the surface membrane.     

Pollen Wall Development in Gibasis (Commelinaceae)

The development of the one and-inline of the pollen wall aredescribed for Gibasis karwinsk yana and G. venustula. Duringthe tetrad stage the appearance of electron-opaque depositionsor tri-partite plates at discrete sites between the plasma membraneof the spore and the inward surface of the callose special wallare the first indications of exine development. The sulcus rapidlydifferentiates being composed of discrete exine granules ona thin foot layer. Probacula in non-apertural areas developin an electron-opaque granular layer situated between the plasmamembrane, which is highly convoluted, and the callose specialwall. A foot layer is formed from electron-opaque lamellae atthe plasma membrane. Exine pattern is clearly established withinthe tetrad. After release of the spores from the tetrad an intimate associationis rapidly developed between the plasma membrane of the periplasmodialtapetum and the newly-formed exine. Compacted electron-opaquematerial is found at the interface between membrane and theexine and vesicular material is added from the tapetum. Theincrease in volume that occurs in both spore and anther is accompaniedby considerable vacuolation. Intine development begins just prior to pollen grain mitosisand continues rapidly at the aperture. The thin foot layer becomesdiscontinuous. Further intine deposition takes place after mitosisand a bilayer is apparent in mature grains. The matrix of thislayer contains conspicuous electron-opaque platelets. The exineof the mature spore stains less intensely than in the youngspore and the interbacula spaces are filled with material fromthe degenerate tapetum. Gibasis karwinskyana, Gibasis venustula, Commelinaceae, exine, intine, tapetum, pollen wall, ultrastructure     

Studies on the Sporogenous Lineage in the Moss Timmiella barbuloides IX. Development of the Tapetum

The ultrastructure of tapetal cells in Timmiela barbuloideswas investigated in relation to events of sporogenesis. Aftertheir establishment both internally and externally to the sporogonialinitials, tapetal cells enlarge and assume a permanently polarizedorganization after completion of meiosis. A large vacuole isformed in the cell region distal to the spore sac, the nucleusbecomes centrally located, and amyloplasts lie in the cytoplasmadjacent to the spore sac. An extensive endomembrane systemdevelops in tapetal cells during the stage of exine depositionin spore tetrads. Sheets of rough endoplasmic reticulum developfirst around the nucleus then also in close proximity to theplasma membrane abutting the spore sac. Concomitantly, interveningdictyosomes produce a variety of vesicles. Unusual structureswith vesicle-like profiles also occur in the inner tapetum cellwalls abutting the spore sac. At the same time most of the starchis lost from the plastids in which grana-fretwork systems develop.A massive secretion of extremely electron-opaque material isassociated with perine deposition onto the free spore surfaces.Degeneration of the tapetal cells during the terminal stagesof spore maturation is marked by distortion of the organelles,increase in vacuolation and the appearance of electron-opaquematerial between the sheets of endoplasmic reticulum.Copyright1994, 1999 Academic Press Bryophytes, endomembrane dynamics, Timmiella, ultrastructure, development, tapetum     

A route for the passage of substances through the developing pteridophyte exine

Summary The developing exine ofLycopodium gnidioides is traversed from the outer to the inner surface by a series of anastomosing channels filled or lined with fibrillar glycoprotein. When living sporangia are incubated in colloidal iron, particles of ferric iron can be detected in the exine channels, the intine and the spore cytoplasm, and some iron is retained by the surface coatings on the spore. Although there is some diffuse iron staining of the exine between the channels, the main concentration of particles is associated with these structures. This, together with the fact that the proximal lasurae of the spore are closed during development, is taken as evidence that the iron has passed from the locular fluid to the surface of the protoplast principally by way of the exine channels. Results obtained from fixation in a glutaraldehyde-lanthanum nitrate mixture support this interpretation. While the exine channels are in existence, therefore, the spore protoplast is in open communication with the locular environment. The study provides no evidence to suggest that the iron which entered the spore cytoplasm did so by endocytosis. It is possible that iron altered the permeability of the plasma membrane by damaging its structure; entry of iron to the cytoplasm being effected through the damaged membrane.     

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.     

Spore Germination Patterns in the Ferns, Cyathea and Dicksonia

Cell division patterns during germination of spores of Cyatheaaustralis, C. cooperi and Dicksonia antarctica were examinedby light microscopy of sectioned materials and by the scanningelectron microscope. In C. australis and C. cooperi the rhizoidwas traced to a small cell formed by an asymmetric divisionof the spore by a wall parallel to its equatorial plane. Incontrast, the rhizoid was formed by a division of the sporeparallel to its polar axis in D. antarctica. In spores of bothgenera, a second division wall oriented in a plane perpendicularto the first gave rise to the protonemal cell. Certain aspectsof germination described here in spores of Cyathea and Dicksoniaare in conflict with the published accounts of spore germinationin these genera. Cyathea, Dicksonia, spore germination, cell division pattern     

The Structure and Function of the Spore Outer Membrane in Dormant and Germinating Spores of Bacillus megaterium

Attempts to demonstrate the presence of the spore outer membrane in mature, dormant spores of a strain of Bacillus megaterium are described. The outer, integument, layers of this organism were found to contain one-third of the total spore cytochrome content, several enzymes of the electron transport chain (specifically NADH oxidase, dehydrogenase, cytochrome c reductase and NADPH dehydrogenase) and a large number of polypeptides extractable with sodium dodecylsulphate in the presence of dithiothreitol and protease inhibitors. These all suggest the presence of a membraneous element. Electron microscopic evidence is presented on the structure of the dormant integument enzymes. Changes in the integument enzymes and in the gel electrophoresis profile of the extractable integument polypeptides which occur during spore gemination, are described and compared with those that take place in the spore inner membrane. The heat sensitivity of the integument enzymes is compared with that of the inner membrane enzymes and the implications for theories of spore heat resistance discussed.     

Observations on the Life History of the Haptophycean Alga Pleurochrysis scherffelii with Special Reference to the Microanatomy of the Different Types of Motile Cells

The coccolith-bearing phase of Pleurochrysis scherffelii hasbeen examined with the electron microscope for the first time.Coccolith and scale structure, haptonema morphology, and themicroanatomy of the protoplast have been recorded and shownto agree closely with those of Hymenomonas carterae and theHymenomonas stage of Apistonema previously investigated by thepresent author. Comparative observations have been made on thevegetative phase and non-coccolith-bearing swarmers of Pleurochrysisscherffelii and these differ significantly in scale morphologyfrom the coccolith-bearing phase although the haptonema of theswarmers is similar. Certain developmental observations havebeen included in the investigation and the taxonomic significanceof the findings is discussed in a preliminary way.     

On the Megaspores of Four Species of Lepidostrobus

This paper is an account of the megaspores borne by four speciesof Carboniferous Lycopod cones, referred to the genus Lepidostrobus.The megaspores (assigned to the genus Triletes) have been knownisolated for more than twenty years, but the identities of theirparent cone species have not previously been established. Thisstudy suggests the limits of variation that can reasonably beallowed in a ‘spore species’. Three of the conespecies are emended in the light of their spore content, anda new species (Lepidostrobus allantonensis) is described. Usingthe megaspores as a diagnostic cone character, it has provedpossible to correlate a species of isolated cone (Lepidostrobusdudius Binney) with the tree which bore it (Lepidodendron smileKidst.). A cone previously attributed on doubtful evidence toBothrodendron is shown to bear megaspores indistinguishablefrom those of a species reliably attributed to Lepidodendron,suggesting that the attribution to Bothrodendron is incorrect.     

The Ultrastructure of the Spores of the Devonian Plant Parka decipiens

The ultrastructure of the spores of Parka decipiens Flemingwas investigated by SEM and TEM. The spores are shown to havea structured wall consisting of two distinct layers, one ofwhich exhibits a lamellate organization. The deposition of thespore wall by a tapetum is suggested to account for these lamellae.Comparison is made between the spore ultrastructure of Parkaand that of algae and bryophytes. It is suggested that the sporewall of Parka bears some similarities with the lamellate exinefound in the Hepaticae. Parka decipiens, Devonian, fossil, spore wall, ultrastructure, lamellae, tapetum     

Ascospore Dimorphism and Mating Type in Chromocrea spinulosa (Fuckel) Petch n. comb

The asci contain four large and four small ascospores, eachtwo-celled, arranged in the six patterns expected if spore sizewere controlled by a pair of allelic genes, the locus showing65 per cent, second-division segregation. The small ascosporesproduce sterile colonies, the large ones moderately fertilecolonies whose asci again show segregation for spore size. Fertilityis stimulated where colonies from large and small spores meet.In crosses of various mutants with the wild type, all asci inperithecia developed along the line of junction show segregationfor the mutant as well as for spore size. Evidently Chromocreais heterothallic, the spore-size difference being a pleiotropicexpression of mating type. One allele, that governing largespores, occasionally mutates to the other allele, resultingin fertility of colonies from large spores.     

Fine structure of the developing spore of Nosema apis zander

Summary The mature spore possesses a thick spore coat and a particle-bearing spore membrane. The highly laminated polaroplast membranes are located at the anterior pole of the spore. Close to its base, the polar filament is surrounded by the polaroplast membrane. The polar filament runs spirally towards the posterior pole of the spore. A large portion of the polar filament is arranged in two layers. A similar arrangement was also observed in immature spores and in the sporoblast stage, although it was not so orderly arranged in the latter. The developing polaroplast membrane was observed in the immature spore, but not in the sporoblast. The sporoblast wall is much thinner than the spore coat, but has the same texture. Endoplasmic reticulum is the most prominent cytoplasmic organelle in the developing stages of Nosema apis. Porous nuclear envelopes are also observed in developing stages. The role of the endoplasmic reticulum in the formation of the polar filament, polaroplast and spore coat, and the function of the spore membrane, are discussed.     

Spore Discharge in Basidiomycetes: III. Spore Liberation from Narrow Hymenial Tubes

The hymenial tubes of Polyporus betulinus were shown to be approximatelycylindrical,and to have a sporulating hymenium over the greater part oftheir surface. Sporophores were tilted through measured anglesfrom the vertical in the field and in the laboratory, and theeffect on spore liberation was measured by determining the numberof spores liberated from particular tubes in standard time.All tilting caused a reduction in spore liberation. The amountof this reduction was found to compare closely with that predictedfrom calculation of the amount of hymenium lying directly abovethe orifice at various angles of tilt. It is therefore concludedthat liberation from the tube can be accounted for by the initialviolent discharge of the spore and gravitational attractionalone. An addendum corrects an earlier paper (1959) in thisseries. It shows that the variation in density of spore depositscollected from Trametes gibbosa was due to air currents in theapparatus, not to variation in sporulation rate.     

Developmental Morphology of Platycerium coronarium (Koenig) Desv

The growth habit and certain developmental aspects of Platyceriumcoronarium (stag's horn fern) are described. Starting from theprimordial stage, the nest and pendulous leaves develop to maturityin 90 and 80 days respectively. The fertile lobe, which is partof the pendulous leaf, reaches its maximum size in 40 days.The morphogenesis of the nest leaf is more variable, and itmatures and deteriorates earlier than the pendulous leaf. Theacrostichoid sorus formation is completed in 3 weeks from inceptionand spore dispersal takes place when the fertile lobe is about100 days old. The area of the fertile lobe and number of sporesproduced were determined. On Knop's agar medium the gametophytesdevelop in 2 months and 85 per cent of them are unisexual (bothmale and female) and 15 per cent bisexual. Less than 1 per centof the gametophytes give rise to sporophytes. The juvenile leavesare simple, displaying open dichotomous venation; the firstnest and pendulous leaves are produced 24 months after the dateof spore germination. Platycerium coronarium, stag's horn fern, leaf development, morphogenesis, spore production     

Development of Sporangiophores of Peronospora parasitica (Pers. ex Fr.) Fr.

The morphology of developing sporangiophores of Peronosporaparasitica from wallflower is described, and morphogenesis maybe divided into the following five stages: the sporangiophoreprimordium, unbranched sporangiophore, branched sporangiophore,spore formation and maturation, and formation of the cross wall.The growth of individual sporangiophores in a humidity chamberwas followed under the microscope, and increase in height andincrease in volume measured. The greatest increase in volumewas during spore formation, when the sporangiophore volume mightquadruple within an hour.     

Ultrastructure of the Sporangiospore of Kickxella alabastrina (Mucorales)

The structure of the sporangiospore of Kickxella alabastrinawas examined by means of carbon replicas, ultrathin sectionsand chemical and physical disintegration. The wall consistsof an outer ornamented, largely amorphous complex and an inner,largely fibrillar complex. The outer complex is disrupted bytreatment in hot dilute alkali whereas the inner complex islargely unaffected. An annulus, similar to that described forCoemansia aciculifera, forms part of the central region of theinner complex and apparently develops prior to liberation ofthe spore from the pseudophialide. A labyrinthiform organelle,attached to the base of the septum which separates the sporefrom the pseudophialide, is described.     

Osservazioni preliminari al microscopio elettronico a scansione sulle ornamentazioni delle spore di Russula

Abstract

Preliminary observations on spore ornementation of Russula, as seen in the scanning electron microscope. — The spores of 16 species of Russula have been examined in the scanning electron microscope, as a preliminary attempt to see if an accurate examination of the spore surface at the ultrastructural level could reveal details of ornamentation which might be useful for the classification of the many species of this genus. The examination, carried out both on fixed and unfixed specimens, has demonstrated that the spore shape is always round or slightly elliptic, and that the obnormal forms as previously described are probably artifacts. Five main types of ornamentation have been described: single wart-like and single finger-like Protrusion, wart- or finger-like protrusions interconnected by thin ridges, and thick, short « papillae » together with large ridges that run along large tracts of the spore circumference. The type of ornamentation was a constant character in each species.