Bernard Lugardon

CHEMICAL STRUCTURE OF THE ORGANIC MATTER IN A PLIOCENE MAAR-TYPE SHALE : IMPLICATED BOTRYOCOCCUS RACE STRAINS AND FORMATION PATHWAYS

Abstract A maar-type Pliocene oil shale from Pula (Hungary) was examined by Scanning and Transmission Electron Microscopy (SEM, TEM) bitumen analysis, spectroscopic analyses (FTIR, solid state 13 C NMR) and pyrolytic analyses of insoluble material. The investigated samples, corresponding to the “massive section” of Pula deposit, exhibit TOC values ranging from 18 to 42%, and Rock-Eval analysis indicated that such samples are comprised of low maturity type I kerogen. Electron Microscopy observations confirmed that recognizable microfossils in this organic matter-rich material almost exclusively correspond to Botryococcus braunii colonies, the morphology of which is perfectly retained. Identification of bitumen and pyrolysate constituents (hydrocarbons, ketones, fatty acids), along with morphological and spectroscopic features, indicate (1) that B. braunii provided a major input to the most organic matter-rich section of Pula oil shale; (2) that both the n -alkadienes-producing and the lycopadiene-producing strains ( A and L , respectively) were present; (3) that the selective preservation of the insoluble and non-hydrolysable macromolecules building up B. braunii outer walls was by far the main process in the formation of this material; (4) that such a process, along with B. braunii prolific growth in the favourable environment that occurred in the crater lake, accounts for the very high TOC and oil potential of Pula deposit; and (5) that the condensation of high molecular weight ether lipids from the A race and of some bacterial lipids also likely contributed to Pula kerogen formation.

Notes on the morphology and fine structure of the exine of some pollen types in dipterocarpaceae

Abstract The pollen morphology of nine species belonging to six genera of Dipterocarpaceae is described in detail with light, scanning electron and transmission electron microscopy, while additional data on twenty-eight species are briefly discussed. In Dipterocarpoideae, grains are tricolpate and the exine consists of a thin, often laminated basal layer and an outer, sculptured layer in which columellae and tectum may either be recognizable or fused into a tilioid structure. The surface of the tectal ridges often show a highly characteristic grooved or crenelated microsculpture. In Monotoideae the grains are tricolporate and four layers can be recognized, the inner two being probably equivalent to endexine s.s. and footlayer, the outer two forming a fairly coarse tilioid reticulate sculpture. The evolutionary relations between the pollen types and their relations to taxonomy, wood anatomy and fruit morphology are discussed. A fair amount of correspondence is obvious, although discrepancies, especially with anatomical evidence, exist also.

Exine formation in Chamaecyparis lawsoniana (Cupressaceae) and a discussion on pteridophyte exospore and gymnosperm exine ontogeny

Abstract Exine ontogeny in Chamaecyparis lawsoniana is similar to that in other gymnosperms investigated as far as modes of wall layer formation are concerned. However, it differs markedly in timing of layer development, inasmuch as endexine elaboration is initiated at the cell surface prior to appareance of tectum and infratectum components at the level of the microspore surface coat. It is observed that the tectum and infratectum are formed through deposition of sporopollenin on receptor sites provided by the microspore surface coat, whereas the foot layer appears to result from accumulation of similar sporopollenin against the endexine surface. It is proposed that the microspore surface coat is part of the microspore glycocalyx and mediates tectum and infratectum formation, while foot layer deposition must be mediated by a distinct, innermost part of this glycocalyx. Comparison of gymnosperm exine and pteridophyte exospore ontogeny shows that, (1) the whole solid, structureless outer part of the exospores is formed through the same process as the foot layer of gymnosperm exines; (2) the ontogenetic and structural differences between the two types of walls are mainly due to the presence of the microspore surface coat in gymnosperms, which produces formation of exine outer strata having very varied organizations, usually including large gaps. The entire pteridophyte exospore appears thus to be ontogenetically homologous to the endexine and foot layer of the gymnosperm exine. It is assumed that the “para-exospore” of Isoetaceae and Selaginellaceae microspores and the comparable extra-exosporal wall of certain fossil spores are formed through intervention of a microspore surface coat-like matrix, and are thus homologous to tectal and infratectal structures of gymnosperm exines.

The microspores of Pleuromeia rossica Neuburg (Lycopsida; Triassic): Comparative ultrastructure and phylogenetic implications

Abstract The ultrastructural features of the microspores of the Triassic lycopsid Pleuromeia rossica are similar to those of the microspores of the living Isoetes , except that the latter have an additional outermost wall. These features differ greatly from those of the spores of all the other extant Pteridophyta. Likewise, the megaspores of P. rossica , of which the comparative analysis will be presented later, are also ultrastructurally analogous to the megaspores of Isoetes . These ultrastructural similarities very likely imply close relationships between Pleuromeia and Isoetes . Moreover they suggest that these genera belong to a distinct group among the heterosporous lycopsids, in which the ultrastructural features of the microspores remained outstandingly steady.

Sur la formation du sporoderme chez Psilotum Triquetrum Sw. (Psilotaceae)

Abstract The stages of the sporoderm morphogenesis of Psilotum triquetrum are studied by TEM from the newly formed tetraspore stage to the release of the spores. First the tetraspores are overlaid with the “foliated substructure of the exospore”, which consists of some long, thin, anastomosed sheets, and shows a protruding narrow fold at the region of the future aperture; thereafter, sporopollenin without a definite structure gradually accumulates on the substructure thus forming the middle and outer parts of the exospore. Finally, a thin perispore develops close to the surface of the exospore. Either simultaneously or with variable delay, a “pseudo-endospore” fairly thick at the apertural region but very thin elsewhere, appears between the exospore and the spore cell. The endospore itself has not developed when the spore release occurs. This ontogenetical process of Psilotum is very similar to that of Filices, whereas it obviously differs from that of other Pteridophytes Les etapes de la morphogenese du ...

Comparative ultrastructure of the megaspores of the triassic lycopsid Pleuromeia rossica Neuburg

The ultrastructural study of the megaspores in Pleuromeia rossica clearly demonstrates that these spores have, besides the features common to the megaspores of all the fossil and recent lycopsids, the few structural characteristics regarded as distinctive of the isoetalean megaspores. These isoetalean characteristics of the megaspores of P. rossica, in addition to the ultrastructural similarities of its microspores with those of the living Isoetes (shown recently), reinforce the assumption of a close relationship between these lycopsids.

Pollen ultrastructure and relationships of Fusaea (Baillon) Safford and Duguetia A. Saint-Hilaire (Annonaceae)

Cladistic analyses indicate that the neotropical genus Fusaea, placed by Walker in his Fusaea tribe along with other genera with large, granular tetrad pollen (e.g. Xylopia, Cananga), does not belong with these genera (our xylopioid clade) but rather with several genera with pseudosyncarpous fruits (Letestudoxa, Duguetia, Pachypodanthium), which together with Uvaria and Toussaintia form our uvarioid clade. TEM observations show that despite the convergence of its pollen with the xylopioids at the LM level. Fusaea differs from that group and resembles other uvarioids in having a nexine consisting of multiple foliations rather than fused granules, plus an unusually thick tectum overlying a thin granular layer. TEM observations confirm that two species of Duguetia have a highly reduced exine consisting a probable remnants of the tectum. Cladograms confirm a trend for exine reduction in the uvarioids, with the spines of Pachypodanthium derived from tectal verrucae, as in Letestudoxa and Duguetia. Radiation of the uvarioids was apparently centered in Africa and South America when the South Atlantic was narrower than it is today.

Le contenu cellulaire du pollen fossilisé dans l'ambre, préservé à l'état organique

The cell contents are still present inside almost every fossil pollen grain embedded in amber of two different origins (Lower Eocene amber from Paris Basin, Tertiary Baltic amber): they are here described after the observation of numerous extracted grains. Some structures are identified, among which probably the nucleus. Because of their confining in this very peculiar fossilization medium, the cell contents were not permineralized but remained somewhat close to the original organic condition, hence offering a field of research about fossil intracellular structure and palaeo-biochemistry, some organic molecules remaining potentially preserved.

Morphologie et ultrastructure du pollen des Siparunaceae (Laurales)

The pollen morphology of Siparuna, Bracteanthus and Glossocalyx, and the ultrastructure of S. decipiens and G. longicuspis

Microspore wall organisation and ultrastructure in two species of Selaginella (Lycophyta) producing permanent tetrads

Abstract Spore morphology and ultrastructural features of the permanent microspore tetrads of Selaginella convoluta and S. lepidophylla were studied with light microscopy, scanning and transmission electron microscopy. The four members of each tetrad in S. convoluta are linked together through a common envelope and form an unbroken complex system of alveoli that connects the equatorial and distal regions of the microspores. In the proximal exospore of microspores, no differentiation referable to an apertural fold was observed but an interruption of the exospore is evident in that area in germinating microspores. The distal exospore is composed of three strata: inner zone, intermediate zone and outer alveolar. In S. lepidophylla tetrads, the four microspores are assembled within a common tetrad envelope and are equatorially connected by a prominent ridge. The distal regions of the microspores are free. In the proximal exospore of microspores, no differentiation referable to an apertural fold was observed. The tetrad envelope appears as a wide common coat, which, on the surface and depending on the regions, is granular or alveolate, centrally perforated and, in section, consists of a single layer or forms a two-layered, more or less intricate, network. This envelope has the same contrast as the exospore outer layer and shows, in its median zone, cavities with opaque contents, quite similar to those of the microspore exospore layer. These two different types of tetrads emphasise the outstanding structural diversity of the microspore sporoderm in living Selaginellaceae.