Papers by Svetlana Polevova
This study of peristome development in Buxbaumia aphylla, B. minakatae and B. viridis has reveale... more This study of peristome development in Buxbaumia aphylla, B. minakatae and B. viridis has revealed major differences from all other peristomate mosses. The fundamental square patterning, characteristic of moss peristome formation, is lacking in Buxbaumia. Endothecium and amphithecium are differentiated, but cells of the endothecium are arranged radially and are likely derivatives of a large tetrahedral central cell. Cells of the inner peristomial layer (IPL) are all offset against cells of the primary peristomial layer (PPL), in both transverse and longitudinal sections. At early stages, IPL cells are 1.2–2 times fewer than PPL cells; subsequently they become about equal in number. However, close to urn base additional anticlinal divisions result in IPL cells double in number to those in the adjacent PPL layer. The maximum number of cells in the PPL is 48 in B. aphylla, but the peristomial formula can be calculated only by counting of all cells in moderately regular cell rings aroun...
Two Aristolochia species are distinguished by microsporogenesis types and time of aperture initia... more Two Aristolochia species are distinguished by microsporogenesis types and time of aperture initiation in the sporoderm development. A. clematitis has successive meiosis and forms an aperture in the late free microspore stage when the intine is maturing. A. manshuriensis has simultaneous microsporogenesis and forms aperture regions in the middle tetrad stage. However, the endexine and intine develop uniformly all over the pollen grain without any differences indicating aperture regions. Strong slowing of intine development at the end of pollen ontogeny allows pollen of A. clematitis to have an aperture which had not been formed at first. Pollen grains of A. manshuriensis, which are tardy up to the stage of intine initiation, do not have enough time to form any aperture in last stages of endexine and intine development. Only deep cracks in the ectexine weakly remind of apertures in A. manshuriensis.
—An open access information system (http://botany-collection.bio.msu.ru) consolidating digital da... more —An open access information system (http://botany-collection.bio.msu.ru) consolidating digital data on palynological, carpological, and wood anatomy collections has been established at the Department of Higher Plants of the Faculty of Biology of Moscow State University. The database includes both digital images and short morphological descriptions of samples collected during the last 70 years. The system has a joint interactive catalogue of all samples included and allows a user to make a search by the names of species, genera, families, and life forms. In addition, each collection has a separate catalogue with various search parameters. The complete catalogues of all collections are also available in Excel file format.
Thirty four species of Campanuloideae (Campanulaceae) from 14 genera were studied with transmissi... more Thirty four species of Campanuloideae (Campanulaceae) from 14 genera were studied with transmission electron microscope. Three type of sporoderm ultrastructure were defined. This result does well correlated with modern systems of Campanulaceae family. The most specific characters are endexine structure and ectexine/endexine ratio. According to tectum structure pollen grains of Campanulaceae are close to Asteraceae.
Andreaeobryum macrosporum is newly found in Yakutia, in the Sette-Daban Mountain Range, ca. 3000 ... more Andreaeobryum macrosporum is newly found in Yakutia, in the Sette-Daban Mountain Range, ca. 3000 km west of its known localities in Alaska. This is the first record of the genus and the class Andreaeobryopsida outside of North America. The species was found on calcareous rock outcrops, above the tree line in the Pinus pumila altitudinal belt. The morphology of the Siberian plants is described, focusing particularly on characters less studied in previous observations. Among these are: (1) axillary hairs with a complicated beak structure, apparently regulating mucilage exudation; (2) anacrogyny and the ability to substitute half of a leaf with an archegonium; (3) specific and relatively long sporophyte development within the epigonium, which is filled with mucilage mixed with macerated cells from the inner wall of the epigonium; (4) foot formed by cells with numerous chloroplasts, with inflated surface cells, sometimes forming finger-like protrusions and with the labyrinth ingrowth in 1–3 layers of the foot surface cells and also labyrinth structures on the surface cell wall facing placental space, whereas gametophyte cells have no ingrowth; (5) lobate archesporial tissue, not fully overarching the columella, which has membranaceous connectives between its segments and reaches the poorly differentiated outer spore sac, being thus similar to Andreaea in many respects; (6) flattened seta, which is not due to drying but lacking radial symmetry from the outset; (7) spore walls lacking or almost lacking an exine. It seems that Andreaeobryum plant possesses an ability to concentrate light, as the physiologically important parts of the structure, the haustorial part of the foot, the urn base, the archegoniophores and the meristematic zones near leaf bases, look considerably brighter in comparison with other parts of the plant.
We have attempted to elucidate the underlying mechanisms of sporoderm development and pattern det... more We have attempted to elucidate the underlying mechanisms of sporoderm development and pattern determination in Plantago major through a detailed ontogenetic study, using transmission electron microscopy (TEM) and scanning electron microscopy (SEM). We aim to compare our observations and interpretation with those on other species. Our study of sporoderm development in Plantago from the early tetrad stage to mature pollen grains has shown that pure physical processes, including self-assembly, which are not under direct genetic control, play an important role and represent evidently one of the instruments of evolution. Our observations fit well with the sequence of self-assembling micellar mesophases and show reiteration of some of them, confirming our self-assembly hypothesis. Some attention was also paid to the possible role of rough and smooth endoplasmic reticulum in the cortical cytoplasm of the developing microspores. The tapetum and Ubisch bodies development are also traced. The importance of detailed ontogenetic studies for understanding the establishment of complex pollen walls in any species and for understanding mechanisms underlying sporoderm development was demonstrated. We also present a simulation, obtained in vitro experiments by self-assembly, mimicking pollen grain of Plantago major. It is clear that, in pollen wall development, biological processes and purely physical factors work in tandem.
Plant Systematics and Evolution, 2014
Pollen grains of Cycadopites-type were found in the pollen chamber of a supposed ginkgoalean seed... more 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.
Review of Palaeobotany and Palynology, 2014
The purpose of this work was to study in detail the successive stages of pollen wall development ... more The purpose of this work was to study in detail the successive stages of pollen wall development in Juniperus communis and intimate connection between the microspores and nutritive tapetum with TEM. Another goal was to clear up the mechanisms underlying the developmental processes. The key stages observed are: the appearance of the initial outer glycocalyx layer as a row of spherical units at the early tetrad stage, followed by the emergence of the underlying radially oriented string-like units, resulting in the formation of a reticulate layer. After sporopollenin accumulation, spherical units turn into granules. String-like units start from the microspore plasma membrane, pierce the glycocalyx layer, pass between the primexine granules and through callose jacket and come out to the anther loculus, reaching the tapetal cells. Their substructure and size are similar to viscin threads, but not their function and chemical composition. All the structures, observed in sporoderm development, correspond to subsequent mesophases of a micellar system. The latter develops by self-assembly, under genomic control, regulating increasing concentration of glycoprotein surfactants in the periplasmic space. A thick network of filaments, connecting microspores and tapetum, supplies microspores with necessary nutrients and testifies the opinion that, in the process of development, exine is a living, dynamic system, arranged from plasmodesmata-like units.
Spores of Oedipodium griffithianum are studied under SEM and TEM, revealing a unique combination ... more Spores of Oedipodium griffithianum are studied under SEM and TEM, revealing a unique combination of characters: distinct trilete laesura, distal surface densely covered by club-shaped papillae often fused by their distal parts, perine mostly eroded and fallen off in the mature spores, and layer between exine and intine strongly variable in size and texture between distal and proximal hemisphere. This layer is homogeneous or occasionally totally absent at distal pole, lamellose in equatorial region in sections of fully developed spores, while indistinctly lamellose to homogeneous in a slightly premature spores; in the proximal hemisphere and in laesura it is thick and has complex structure. In somewhat premature spores an electron dense perine is observed upon exine, but it seems to easily fall off during spore maturation, so fully mature spores almost lack perine like in Bruchia brevifolia. Oedipodium is similar to Sphagnopsida in distinct laesura, unstable perine and complex multilaminate innermost layer of exine, a remnant of tripartite lamella.
The purpose of this study was to investigate the sporoderm development of inaperturate pollen gra... more The purpose of this study was to investigate the sporoderm development of inaperturate pollen grains in Aristolochia clematitis (Aristolochiaceae). During successive microsporogenesis several types of tetrads are formed; no tetrahedral tetrads were observed. In the tetrad period, the primexine is observed around the perimeter of microspores. In the free microspore period, a thick lamellar endexine develops around the perimeter of the microspore; the thick tubular intine appears later in this period. At the maturation of pollen grains, the intine is stratified into two layers: an outer tubular ectintine and an inner homogeneous endintine. Finally, the intine forms an aperture thickening. The thickened intine deforms and displaces the endexine and tears the ectexine apart. This shows that pollen grains of A. clematitis are aperturate. The apertures are colpi.
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Papers by Svetlana Polevova