Studies on Timmiella barbuloides (Brid.) Moenk., IV. SEM and TEM characterization of spore wall and first germination stages

Abstract

The spore wall morphology of Timmiella barbuloides (Pottiales, Musci) is described. The spores are catalept, with an ornamentation pattern consisting of unevenly spaced, shortly pedunculated pilum-and gemma-like processes. The spore coat consists of three, unevenly thick layers: intine, exine, and perine. The exine is not involved in wall ornamentation, the processes consisting of perine only. The leptoma, a spore coat area involved in germination, consists of an intine markedly thickening in an area of thinning exine and, outside, with a spore coat area where perinous processes become sparse. On the basis of observations and of the data reported in recent literature the classical definition of the leptoma is modified. It is considered to be a structurally specialized, but not necessarily thin, area.     

SPORE WALL DEVELOPMENT IN ANDREAEA (MUSCI: ANDREAEOPSIDA)

The spore wall of Andreaea rothii (Andreaeopsida) is unique among mosses studied by transmission electron microscopy. The exine of other mosses is typically initiated on trilaminar structures of near unit membrane dimensions just outside the plasma membrane. The exine of Andreaea is initiated in the absence of such structures as discrete globules within the coarsely fibrillar network of the sporocyte wall. The sequence of wall layer development, nevertheless, is essentially like that of other mosses. The intine is deposited within the exine and the perine accumulates on the surface of the exine during the latter stages of spore maturation. The mature spore is weakly trilete and inaperturate. The wall consists of three layers, the inner intine, the spongy exine consisting of loosely compacted irregular globules of sporopollenin, and an outer layer of perine. The perine differs ultrastructurally from the exine only in its greater degree of electron opacity. This ultrastructural evidence of departure from the fundamental pattern of exine development in mosses supports the taxonomic isolation of Andreaea from mosses of the Sphagnopsida and Bryopsida.     

PpASCL,the Physcomitrella patens Anther-Specific Chalcone Synthase-Like Enzyme Implicated in Sporopollenin Biosynthesis,Is Needed for Integrity of the Moss Spore Wall and Spore Viability

Sporopollenin is the main constituent of the exine layer of spore and pollen walls. The anther-specific chalcone synthase-like (ASCL) enzyme of Physcomitrella patens, PpASCL, has previously been implicated in the biosynthesis of sporopollenin, the main constituent of exine and perine, the two outermost layers of the moss spore cell wall. We made targeted knockouts of the corresponding gene, PpASCL, and phenotypically characterized ascl sporophytes and spores at different developmental stages. Ascl plants developed normally until late in sporophytic development, when the spores produced were structurally aberrant and inviable. The development of the ascl spore cell wall appeared to be arrested early in microspore development, resulting in small, collapsed spores with altered surface morphology. The typical stratification of the spore cell wall was absent with only an abnormal perine recognisable above an amorphous layer possibly representing remnants of compromised intine and/or exine. Equivalent resistance of the spore walls of ascl mutants and the control strain to acetolysis suggests the presence of chemically inert, defective sporopollenin in the mutants. Anatomical abnormalities of late-stage ascl sporophytes include a persistent large columella and an air space incompletely filled with spores. Our results indicate that the evolutionarily conserved PpASCL gene is needed for proper construction of the spore wall and for normal maturation and viability of moss spores.     

Spore morphology of some Bruchiaceae species (Bryophyta) from Brazil

The spores of Bruchia uleana, B. uruguensis, Eobruchia bruchioides, Trematodon ambiguus, T. aureus, T. brevifolius, T. longlcollis, T. reflexus and T. vaginatus were studied by light and scanning electron microscopy. The spore wall of the family Bruchiaceae includes sclerine (the distinction between exine and perine may be difficult to define) and intine. The aperture may be surrounded or not by one or more rings of ornamentation elements. Two basic types of spore were recognized: one characterized by a gemmoid surface and the other with elongated processes and two types of ornamentation in the apertural region. The spores of the taxa studied support the separation of the Bruchiaceae from the Dicranaceae.     

Studies on Spore Morphology of Some Chinese Sphagnum L

The spores of 5 species and 1 subspecies of Sphagnum in China were examined under LM and SEM, and one of them under TEM. All of the above spores are radial symmetrical, tetrahedral, rounded-triangular in polar view and 36.1-55.7 μm in diameter. Among them, the size of the spores of S. cuspidatum is the largest. Trilete is distinct, narrow and slightly curved, ca. 1/3-1/2 of the spore radius, margo very distinct under SEM, perine with gemmae and verrucae. The sporoderm of Sphagnum contains perine, exine and intine. On the basis of spore morphology, the point of view that Sphagnum is a primitive genus in mosses is supported. In sporo-pollen analysis the spores of Sphagnum are easily confused with some spores of ferns.     

ULTRASTRUCTURE OF SPOROGENESIS IN A MOSS,DITRICHUM PALLIDUM. III. SPORE WALL FORMATION

Ultrastructural evidence indicates that marked cytoplasmic polarity occurs during wall and aperture ontogeny in spores of the moss (Musci), Ditrchum pallidum (Hedw.) Hampe. Shortly after cytokinesis, an extensive system of microtubules underlies the entire distal spore surface where exine deposition is initiated. These microtubules appear to be focused on the plastid. The apposition of slips nearly of membrane dimension contributes to the forming exine. As the lamellate exine thickens and extends to the proximal surface, the plastid and associated nucleus migrate to the proximal surface where an elaborate system of microtubules involved in aperture development is generated. The exine gradually loses its stratiform character, becoming homogenous and eventually papillate. At maturity, the spore wall consists of four layers, the outermost perine, the exine, a separating layer, and the intine. The aperture is a complex, localized modification of these layers on the proximal surface. It consists of a pore containing a fibrillar material surrounded by a thin annulus.     

Ultrastructure of the spore in four Japanese species of Ptychomitrium Fürnr. (Musci)

The ultrastructure of the mature spore in four Japanese species of the acrocarpous moss genus Ptychomitrium is presented. In all species the spores have a similar pattern: there is no recognisable aperture nor sporoderm polarity, exine and perine are poorly developed, cytoplasm only occasionally shows polarity, and plastids have a well developed inner membrane system. The presence of frequent intine protrusions is a remarkable feature of this genus. A multilaminar structure of the exine, already observed in Grimmia, occurs also in these species although here it is less pronounced. The significance of these features is discussed within these species, as well as in comparison to other taxa, especially the genus Grimmia.     

Palynology of selected species of Fissidens (Hedw.)

Spores from 19 species of the subgenus Aloma Kindb. of the moss genus Fissidens were analyzed by light and scanning electron microscopy. Aloma is the largest subgenus of Fissidentaceae and is characterized by the presence of a peristome of scariosus type. The spores of the subgenus Aloma are present in monads, size small to very small, heteropolar, plano-convex, with a proximal aperture region, and the sporoderm is formed by a perine, exine, and intine. The intine is not stratified, the exine is psilate, and the perine granulated. The ornamentation elements may occur singly or grouped on the surface of the spore. The aperture region shows irregular contours, ranging from circular to elongated, due to the weakness of the sporoderm proximal pole. The observed variations among species are related to different patterns of distribution of the sporoderm granules and nanogranules. Quantitative analysis combined with qualitative results did not allow all species of the subgenus Aloma to be distinguished. The results of this study demonstrate that the spore is a useful tool for taxonomic studies, and suggest that its characters be included in phylogenetic analyses, to assist in the reconstruction of the evolutionary history of mosses.     

Observations of spore morphology of some Pottiaceae Schimp. species (Bryophyta) in Turkey

The spores of Syntrichia ruralis (Hedw.) F. Weber and D. Mohr., S. princeps (De Not.) Mitt., S. subulata (Hedw.) F.Weber and D.Mohr var. subulata, S. subulata (Hedw.) F.Weber and D.Mohr var. angustata (Schimp.) J.J. Amann and S. subulata (Hedw.) F.Weber and D.Mohr var. graeffii Warnst. were studied by light and scanning electron microscopy for the first time. The apertural region consists of a leptoma in all spores. All taxa of the family are uniform in their spore morphology. The spores of the five taxa are of granuloid type. The spore wall of the Pottiaceae family includes sclerine (the distinction between exine and perine may be difficult to define) and intine. The taxonomy of the genus Syntrichia is discussed on the basis of its spore morphology.     

SPORE MORPHOLOGY IN THE CYATHEACEAE. II. THE GENERA LOPHOSORIA,METAXYA, SPHAEROPTERIS,ALSOPHILA, AND NEPHELEA

Scanning electron microscopy and transmitted light microscopy are used in a palynological study of Lophosoria, Metaxya, Sphaeropteris, Alsophila, and Nephelea of the tree fern family Cyatheaceae. The monotypic American genera Lophosoria and Metaxya each have a unique spore morphology which reinforces the taxonomic distinctness of these genera as indicated by their other characters. All investigated paleotropical species of Sphaeropteris develop a single type of perine characterized by coarse, pointed projections. In the neotropics, the Sphaeropteris horrida group shares this perine type, whereas all other neotropical Sphaeropteris species appear to have a different kind of perine with fine hair-like processes. The exine in paleotropical Sphaeropteris appears uniformly unsculptured, whereas in the neotropics several exine morphologies are found. In Alsophila all investigated neotropical species and the vast majority of the paleotropical species are characterized by a basically ridged perine morphology and an unsculptured exine. In several paleotropical Alsophila species, however, a perine with hair-like processes similar to those in neotropical Sphaeropteris is found, and the exine in several species is variously pitted. In at least one paleotropical Alsophila species, the porate exine morphology is indistinguishable from that in the neotropical genus Cnemidaria. The spores of the American genus Nephelea are similar to those of the majority of Alsophila species in ridged perine morphology and unsculptured exine. Several new instances of atypical spore numbers per sporangium are reported in Sphaeropteris and Alsophila. These and the palynological data are discussed in a taxonomic framework. The spore morphology in these genera is consistent with Tryon's recent generic revision of the family.     

Ultrastructural investigations on sporogenesis inEquisetum fluviatile

Summary The spore mother cells ofEquisetum fluviatile undergo meiotic division, each forming a tetrad of spores. The spore protoplasts are separated from each other by an accumulation of mitochondria (organellar plate) at first and later on by plasma membranes, no cell wall is formed. The first layer of the sporoderm, the exine, originates from the plasmodial tapetum and is deposited at the outer side of the plasmalemma of the young spore. The exine reaches a thickness of about 330 nm. In the phase of spore greening the so-called perine, originating from the tapetum, is placed onto the exine and the inner layer of the sporoderm, the intine, is formed from the spore protoplast. The mature spore, about 40 m in diameter, does not enter dormancy and remains viable only for a few days.Member of the Study group on electron microscopy at the TierÄrztliche Hochschule Hannover.     

Spore morphology of some Brachytheciaceae Schimp. species (Bryophyta) from Turkey

The spores of Homalothecium sericeum (Hedw.) Schimp., Brachythecium populeum (Hedw.) Schimp., B. velutinum (Hedw.) Schimp. var. salicinum (Schimp.) Mönk., B. velutinum (Hedw.) Schimp. var. validum C. Jens. and Eurhynchium hians (Hedw.) Sande Lac. were studied by light and scanning electron microscopy for the first time. The apertural region consists of a leptoma in all spores. Two spore types, characterized by their surface ornamentation, are established, reflecting the species taxonomic relationships. While the surface ornamentation is of the insuloid type in Eurhynchium hians, it consists of a granuloid type in Homalothecium sericeum , Brachythecium populeum , B. velutinum . var. salicinum, B. velutinum var. validum. The spore wall of the family Brachyteciaceae includes sclerine (the dinstinction between exine and perine may be difficult to define) and intine. The taxonomy of the genera Brachytecium and are discussed on the basis of their spore morphology.     

SPORE WALL ULTRASTRUCTURE IN THE LIVERWORT ATHALAMIA HYALINA

Mature spores of Athalamia hyalina (Marchantiales, Cleveaceae) were examined with both scanning and transmission electron microscopes. Single, hollow, dome-like projections, sometimes having small pores and a coarsely granular surface texture, stud the spore surface, usually in a pattern of concentric circles. In section, the spore wall has an intine and two-layered exine. Intine-like material separates some lamellae of the inner exine, which is joined to the outer exine around the dome bases. Inner exine lamellae are composed of thin (5–6 nm), closely parallel membrane-like subunits. The outer exine is formed from a single large highly modified and doubly-coated lamella, the undulations of which form the surface domes. Dome cavities often are filled with a loose network of granular material.     

SPORE MORPHOLOGY IN THE DICKSONIACEAE. I. THE GENERA CYSTODIUM,THYRSOPTERIS, AND CULCITA

The most mature spores available in herbarium specimens of the dicksoniaceous genera Cystodium, Thyrsopteris, and Culcita were studied by scanning electron microscopy and light microscopy, and representative specimens were analyzed to determine the number of spores produced per sporangium. Thyrsopteris and Culcita feature 64-spored sporangia, but Cystodium is consistently 32-spored. Spores were analyzed both in their native state as found on the specimens and in a perine-free state achieved by treatment with sodium hydroxide or acetolysis mixture. The sodium hydroxide assay demonstrated the presence of a perine in Cystodium, Thyrsopteris, and Culcita subgenus Culcita, but no evidence of a perine so defined was found in Culcita subgenus Calochlaena. Spores of Cystodium feature a nearly psilate exine overlain by a striate inner perine and a granular outer perine and are in several respects similar to those of Metaxya in the cyatheoid-dicksonioid complex and to those of Saccoloma in the dennstaedtioids. The most mature Thyrsopteris spores available may not have been fully mature. They feature a sparsely distributed, granular perinous layer over a microverrucate sculptine. The latter topography is taken as largely perinous since treatment with sodium hydroxide left a nearly psilate exine. The spore morphologies of Cystodium and Thyrsopteris reinforce the taxonomic distinctness of these monotypic genera indicated by their other characters. The two subgenera of Culcita are very dissimilar in their spore morphologies. The exine in subgenus Culcita ranges from psilate to slightly microverrucate proximally and distally, with varying margo development. Spores of subgenus Calochlaena are strongly differentiated from those of subgenus Culcita by their exine of broad spinules which vary in their degree of lateral fusion to each other and in the granular appearance of their distal surfaces. Spore morphology in Culcita strongly supports the argument of those who would raise its subgenera to generic rank.     

SPORE MORPHOLOGY IN THE CYATHEACEAE. III. THE GENUS TRICHIPTERIS

Scanning electron microscopy supported by light microscopic L-O analysis is used in a palynological study of the genus Trichipteris of the tree fern family Cyatheaceae. The spores of all but two of the 55 species are investigated and the results are related to previous findings for Trichipteris species in the literature. A perine layer consisting of a network of slender, smooth- or rough-textured interlocking strands with free ends uniformly characterizes the genus and is the same as the perine type previously reported in neotropical species of Sphaeropteris excluding the S. horrida group. The exine is analyzed both in spores which have not yet developed the perine layer and in spores whose perine has been removed by chemical treatment. Exine sculpturing shows great variation in the genus, ranging from essentially psilate to variously pitted (foveolate, foraminate), with topography ranging from plane to verrucate-tuberculate, and with the verrucae-tubercles themselves often variously pitted. In many instances, exine sculpturing types correlate with the infrageneric species groupings or affinities hypothesized by the recent monographers. In other cases, palynological characters offer new insight into species relationships that were previously unclear to monographers or that were interpreted differently on the basis of other characters. The exine sculpturing types reinforce the relationship evident between Trichipteris and neotropical Sphaeropteris on the basis of perine morphology.     

SPORE DEVELOPMENT IN THE LIVERWORT RICCARDIA PINGUIS

The ontogeny of spores of the liverwort Riccardia pinguis was studied at the light and electron microscope levels. Three stages of development were arbitrarily defined: spore mother cell (SMC); early tetrad with nonpigmented and unsculptured walls; and mature tetrad with pigmented and sculptured spore walls. The SMC is quadrilobed with a two-layered SMC wall, containing a central nucleus, many chloroplasts, spherosomes, and other organelles. During and following meiosis cell plates form from coalescing Golgi vesicles. These plates by continued coalescence eventually form a septum, completing the tetrad. This septum comprises middle lamella and primexine; within the latter the exine forms. By continued addition of vesicle contents to the septum and dorsal surfaces of the tetrad, the exine (sexine and nexine) and intine layers of the spore wall are laid down. The contents of the vesicles change successively during wall formation, corresponding to the different wall layers being formed. It is concluded that wall formation is under the exclusive control of the spore protoplast, and that the pattern of the mature exine is determined by the primexine. Rearrangement of organelles and other cellular components during sporogenesis is described.     

SPORE MORPHOLOGY OF ANEMIA,MOHRIA, AND CERATOPTERIS (FILICALES)

Spores of the ferns Anemia and Mohria (Schizaeaceae) and Ceratopteris (Pteridaceae) are surveyed with light microscopy and scanning and transmission electron microscopy. In each genus the spores are trilete with radially symmetrical exine sculpture comprising three sets of parallel or near-parallel muri. Anemia has six spore types. One is reticulate (A. wrightii-type), and the other five types have either cicatricose or canaliculate sculpture that reflect a basic form, i.e., three mural sets that have mutual anastomoses in each radial region. The cicatricose A. mexicana- and the canaliculate A. dregeana-types represent the simplest expressions of this pattern. Specializations include cicatricose, auriculate (A. raddiana-type) and canaliculate, ornate (A. oblongifolia-, A. phyllitidis-types). Exine structure is homogeneous or differentially microporate; the enveloping two-layered perine has granulate structure and a granulate to spiculate and/or pitted surface. Mohria spores have a stratified, granulate to rugulose perine and cicatricose exine sculpturing consistent with the A. mexicana-type pattern, but the muri are hollow. The canaliculate spores of Ceratopteris differ from those of Anemia and Mohria in that the three mural sets are discrete and separated from each other by a stria in each radial region; exine structure is homogeneous and the thin perine is granulate. Within Anemia the A. raddiana-type is exclusive to subgen. Coptophyllum and the A. oblongifolia- and A. phyllitidis-types to subgen. Anemia. Three spore types are shared by two subgenera; i.e., A. wrightii- and A. mexicana-types in Coptophyllum and Anemirhiza, and the A. dregeana-type in Anemirhiza and Anemia. Spore polymorphism is indicated in several species of subgen. Anemia, and smooth immature spores are recorded from all three subgenera.     

AN ULTRASTRUCTURAL STUDY OF SPORE WALL MORPHOGENESIS IN EQUISETUM ARVENSE

Spore wall morphogenesis of Equisetum arvense was observed by transmission electron microscopy. The spore wall of E. arvense consists of four layers: intine, exine, middle layer, and elater. The exine is formed after meiosis and consists of two distinct layers. The inner portion of the exine is formed in advance of the outer layer of the exine. The middle layer is deposited after the exine. The elater can be subdivided into two distinct layers. The inner layer comprises longitudinal microfibrils that surround the spore in spiral fashion. The elater appears as thin beltlike structures at the beginning of development. Numerous microtubules were observed on the inner surface of the plasmodial plasma membrane opposite the inner layer of the elater, suggesting that these microtubules are involved with the synthesis of inner elater microfibrils. The matrix of the outer elater is formed by discharge of granules from the plasmodial cytoplasm. The intine is the last component of the sporoderm to be formed.     

Experimental alterations of the spores of lycopodium clavatum as related to diagenesis

Lycopodium clavatum spores have been heated to different temperatures at atmospheric pressure, at room temperature with 0.5 kbar pressure and at different temperatures with 1 kbar pressure, The effects of heat, pressure, and heat and pressure together on the spore have been examined in detail using different microscope techniques. Effects of some chemicals on these spores have also been observed.It is known that temperature and pressure change the colour of spore and pollen grain walls, mainly the exine (outer wall of the spore). Changes to the intine and the matter present in the cytoplasmic cavity (= inner contents), however, have not been taken into account by very many workers. In most of the previous works the inner contents were extracted before the experimental treatment began.In the present work, unextracted spores are used for the experiments which show two types of alterations of the spores with rising temperature at atmospheric pressure: (1) alteration of the inner contents, i.e. gradual colour change of the inner contents and their ultimate exudation from the spore through the exine at about 300°C; (2) gradual shrinkage of the exine due to the exudation of the inner contents which also causes an overall size reduction of the spore from 200° to 350°C. The exine does not change its colour up to 325°C; and this temperature, its starts to change its colour slowly, amalgamates with other exines of the empty spores, becomes amorphous, and ultimately deteriorates into unidentifiable organic matter.The process of colour change of the inner contents of spores and the general deformation are much slower when the spores are subjected to 1 kbar pressure with rising temperatures. Spores at room temperature with 0.5 kbar pressure show no colour change but only physical deformation.     

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