Natalia Zavialova

THE POLLEN ULTRASTRUCTURE OF WILLIAMSONIELLA CORONATA THOMAS (BENNETTITALES) FROM THE BAJOCIAN OF YORKSHIRE

The exine ultrastructure of Williamsoniella coronata Thomas from the Bajocian of Yorkshire (United Kingdom) was investigated with light, scanning electron, and transmission electron microscopy. The pollen averages 16.5 μm along its short axis and 24.5 μm along its long axis and is monosulcate, and the nonapertural sculpturing is distinctly verrucate. The pollen wall is homogeneous, and the sulcus membrane is composed of thin exine with scattered small granules. The pollen grains differ in exine sculpturing and pollen wall ultrastructure from pollen grains of the bennettitalean taxa Cycadeoidea dacotensis (MacBride) Ward and Leguminanthus siliquosis (Leuthardt) Kraeusel. They are similar to dispersed pollen grains of Granamonocolpites luisae Herbst from the Triassic Chinle Formation of the United States, supporting the bennettitalean affinity of these dispersed pollen grains. The Bennettitales are palynologically characterized by monosulcate “boat‐shaped” pollen with a homogeneous or granular pollen wall ultrastructure.

On some peculiarities of sporoderm structure in members of the Cycadales and Ginkgoales

The pollen morphology and ultrastructure of Cycas micholitzii, C. simplicipinna, Cycandra profusa, Ceratozamia mexicana, and Ginkgo biloba are studied. Pollen germination is also studied in C. mexicana and G. biloba. Although dehydrated pollen grains appear monosulcate, the study of hydrated pollen shows that the aperture occupies nearly half of the pollen surface and represents a pore rather than a sulcus. In the Ginkgoales, the inaperturate ectexine is characterized by a thick solid tectum, infratectum of columella-like elements or large granules, and distinct foot layer. On the contrary, in the Cycadales, the ectexine consists of a thin tectum, alveolar infratectum, and poorly discernable foot layer. Members of the Ginkgoales have a distinct distal aperture, which is constituted by an intine, endexine, and thin ectexine. In the modern Cycadales, an ectexine is well developed throughout the pollen perimeter; in the supposed aperture region the ectexine is not reduced in thickness, although it is characterized by a thinner tectum and thinner walls of infratectal alveoli. In Cycandra profusa, no unequivocal aperture region has been found. Thickened regions were observed in the intine of both the Cycadales and Ginkgoales.

Exine morphology and ultrastructure of Duplicisporites from the Triassic of Italy

A morphological study of dispersed Circumpolles pollen grains from the Upper Triassic of the Southern Alps has been initiated with the genus Duplicisporites. Individual pollen grains were studied by means of scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Seen with SEM the pollen surface is finely verrucate with low verrucae of different sizes. A sub‐equatorial continuous rimula is clearly visible. The proximal trilete scar is small and indistinct. TEM images reveal a bi‐layered exine. The ectexine is formed by numerous small, closely packed, granulae subdivided by irregularly‐spaced cavities. In the region of the subequatorial canal, the ectexine becomes thinner, about 1/3 of the usual thickness. At places, the ectexine is slightly separated from the underlying endexine. The endexine is prominent and significantly darker than the ectexine. It is homogeneous and of constant thickness. On the basis of its older age, with respect to Classopollis, the present ultrastructural dataset provides information on the possible origin of cheirolepidiaceous‐type morphology.

The fine morphology of pollen grains from the pollen chamber of a supposed ginkgoalean seed from the Middle Jurassic of Uzbekistan (Angren locality)

Pollen grains of Cycadopites-type were found in the pollen chamber of a supposed ginkgoalean seed Allicospermum sp. from the Middle Jurassic deposits of Uzbekistan (Angren locality). The pollen grains were studied with help of LM, CLSM, SEM, and TEM. All pollen grains show the identical morphology and exine ultrastructure allowing us to suppose the same botanical affinity. The pollen morphological data do not contradict the ginkgoalean interpretation of the seed; therefore, the pollen grains and the seed most probably did belong to the same parent plant. The pollen grains are monosulcate, the non-apertural surface is nearly psilate, with low short elements, which are occasionally scattered over the surface or more densely distributed. The aperture and adjacent areas appear to bear more distinct sculpturing. The ectexine is composed of a prominent solid tectum, a thin infratectum, and a thin foot layer. The infratectum is formed of one row of alveolae, which are more voluminous laterally, where the ultrastructure is more easily understandable. The endexine is multilamellate, although it is evident only in some regions of stained sections. Towards the aperture the ectexine becomes gradually thinner; over the aperture no sublayers can be discerned within the ectexine. The ectexine of the apertural region repeatedly varies in thickness, reflecting a sculpturing surface of this region. The obtained data contribute to the knowledge about the exine ultrastructure of ginkgoaleans; nonetheless, a TEM study of ginkgoalean pollen grains extracted from pollen organs is still highly desirable. We also considered pluses and minuses of CLSM: it failed to substitute SEM, since the surface pattern under study was too fine, but demonstrated the general morphology of the pollen grains under study better than conventional LM. The possibility of viewing virtual sections of any area of the pollen grain was profitable for later interpretation of TEM sections. CLSM would give better results in interpreting relatively large palynological objects with distinct sculptural elements, a complicated architecture, variously arranged appendages, or possessing cameras.

The ultrastructure of fossil dispersed monosulcate pollen from the Early Cretaceous of Transbaikalia, Russia

Abstract The general morphology, surface sculpturing, and exine ultrastructure have been studied in dispersed monosulcate pollen from the Early Cretaceous of Transbaikalia, Russia. The pollen grains dominate the palynological assemblage extracted from coal deposits of the Khilok Formation in the Buryat Republic, which also contain ginkgoalean leaves of Baierella averianovii as the only constituent of the assemblage of plant megafossils. The relationship between the pollen grains and ginkgoalean leaves from this autochthonous burial is hypothesised on the basis of taphonomical analysis and palaeobiogeographical data. It is shown that the ectexine of the pollen grains includes a thick solid tectum, a thin granular infratectum and a thin foot layer; the endexine is fine-grained, slightly more electron-dense than the ectexine, and is preserved only in places. The distal aperture is formed by a thinning of the exine. No analogous ultrastructure has been described so far in fossil pollen grains of this morphotype studied ultrastructurally from in situ material. For comparison, we also studied the exine ultrastructure of pollen grains Ginkgo biloba. The fossil pollen is not identical to pollen of extant G. biloba, but shows several significant similarities in the exine ultrastructure, which does not contradict the presumable ginkgoalean affinity of the fossil pollen.

A New Microsporangiate Organ from the Lower Carboniferous of the Novgorod Region, Russia

A new species of the genus Telangiopsis, T. nonnae O. Orlova et Zavialova, was described on the basis of a microsporangiate organ from the Lower Carboniferous deposits of the Novgorod Region. The morphology of branching fertile axes, synangia, and sporangia was thoroughly studied. The three-dimensional system of fertile axes branches monopodially; ultimate axes bear numerous connivent bunches of synangia, which consist of three to six basally fused elongated ovate sporangia. The morphology and ultrastructure of prepollen grains were studied, which were extracted from the rock matrix surrounding the sporangia. The two-layered exine includes a well-developed endexine and an alveolate ectexine, with one-three rows of large thin-walled alveolae. The new species was compared with other Early Carboniferous microsporangiate organs.

Exine ultrastructure in pollen grains of Classopollis Pflug from the Cretaceous of Lebanon

Pollen grains of Classopollis Pflug from the Cretaceous deposits of Lebanon were studied by means of light and electron microscopy. Ultrastructurally, they are similar to pollen grains, extracted from Classostrobus comptonensis Alvin, Spicer et Watson from the Barremian of England. The differences concern the shape and size of spinules, ultrastructure of apertural regions, and preservation of the endexine. An analysis of our data and published results revealed three types of infratectum existed in members of Circumpolles: (1) with branchy elements, (2) with columella-like non-branching elements, and (3) with large granules arranged in one row. The palynological assemblage is described in detail; problems of dating are discussed.

The use of the scanning electron microscope (SEM) to reconstruct the ultrastructure of sporoderm

SEM data can help in interpretation of TEM ultrathin sections and reconstruction of 3-D inner structure of large palynological objects like megaspores. For a SEM study of the inner structure of fossil megaspores, we have tried three variants of embedding media: a water solution of glycerine and gum arabic, a water solution of sucrose and polyvinylpyrrolidone, and a mixture of epoxy resins. Semithin sections of fossil megaspores were made, the embedding medium was removed from the sections, and they were observed under SEM. Epoxy mixture as an embedding medium and Maxwells solution as a solvent turned to be the most appropriate for our purposes. The most suitable way of processing is to embed the object, cut it by turns in semithin and ultrathin sections, and study them with SEM and TEM correspondingly. A combination of SEM and TEM data results in a more profound reconstruction of the inner structure of sporoderms. We used as test objects dispersed megaspores of a supposed lycopsid affinity identified as ...Scanning electron microscope (SEM) data can help in the interpretation of transmission electron microscope (TEM) ultrathin sections and reconstruction of the three-dimensional inner structure of large palynological objects like megaspores. For a SEM study of the inner structure of fossil megaspores, we tried three variants of embedding media: a water solution of glycerine and gum arabic, a water solution of sucrose and polyvinylpyrrolidone, and a mixture of epoxy resins. Semithin sections of fossil megaspores were made, the embedding medium was removed from the sections and they were observed under SEM. Epoxy mixture as an embedding medium and Maxwells solution as a solvent turned out to be the most appropriate for our purposes. The most suitable way of processing is to embed the object, cut it by turns in semithin and ultrathin sections, and study them with SEM and TEM correspondingly. A combination of SEM and TEM data results in a more profound reconstruction of the inner structure of sporoderms. We used as test objects dispersed megaspores of a supposed lycopsid affinity identified as Maexisporites rugulaeferus Karasev et Turnau 2015 and Otynisporites tuberculatus Fuglewicz 1977. The materials studied are from the Lower Triassic and Upper Permian of the Russian Platform.

SEM helps to reconstruct sporoderm ultrastructure

SEM data can help in interpretation of TEM ultrathin sections and reconstruction of 3-D inner structure of large palynological objects like megaspores. For a SEM study of the inner structure of fossil megaspores, we have tried three variants of embedding media: a water solution of glycerine and gum arabic, a water solution of sucrose and polyvinylpyrrolidone, and a mixture of epoxy resins. Semithin sections of fossil megaspores were made, the embedding medium was removed from the sections, and they were observed under SEM. Epoxy mixture as an embedding medium and Maxwells solution as a solvent turned to be the most appropriate for our purposes. The most suitable way of processing is to embed the object, cut it by turns in semithin and ultrathin sections, and study them with SEM and TEM correspondingly. A combination of SEM and TEM data results in a more profound reconstruction of the inner structure of sporoderms. We used as test objects dispersed megaspores of a supposed lycopsid affinity identified as ...Scanning electron microscope (SEM) data can help in the interpretation of transmission electron microscope (TEM) ultrathin sections and reconstruction of the three-dimensional inner structure of large palynological objects like megaspores. For a SEM study of the inner structure of fossil megaspores, we tried three variants of embedding media: a water solution of glycerine and gum arabic, a water solution of sucrose and polyvinylpyrrolidone, and a mixture of epoxy resins. Semithin sections of fossil megaspores were made, the embedding medium was removed from the sections and they were observed under SEM. Epoxy mixture as an embedding medium and Maxwells solution as a solvent turned out to be the most appropriate for our purposes. The most suitable way of processing is to embed the object, cut it by turns in semithin and ultrathin sections, and study them with SEM and TEM correspondingly. A combination of SEM and TEM data results in a more profound reconstruction of the inner structure of sporoderms. We used as test objects dispersed megaspores of a supposed lycopsid affinity identified as Maexisporites rugulaeferus Karasev et Turnau 2015 and Otynisporites tuberculatus Fuglewicz 1977. The materials studied are from the Lower Triassic and Upper Permian of the Russian Platform.

The ultrastructure of some Rhaetian Circumpolles from southern England

Abstract The morphology and exine ultrastructure of Classopollis torosus, C. meyeriana and Geopollis zwolinskae are studied from the Cotham Member of the Lilstock Formation (Penarth Group) in southern England. The palynological assemblage that allows dating the deposits to the Rhaetian is outlined. Although the Circumpolles pollen grains under study show variations in the exine ultrastructure, some common characters support their origin from the same plant group, the Cheirolepidiaceae. An infratectum formed by large granulae arranged mostly in one row and sandwiched between the tectum and endexine is considered as the key character of the pollen grains under study. Ultrastructural transformations within Circumpolles are discussed. The origin of Classopollis-producing plants from any plant group with saccate pollen and alveolate ectexine is considered much less probable than from a group with non-saccate pollen with granular ectexine.