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1.
Nina Gabarayeva 《Review of Palaeobotany and Palynology》2006,138(2):121-139
In this article, we analyse established details of exine development from a perspective that favours the integration of self-assembly. We isolate those intervals in development in which genomic control is exercised and offer a number of scenarios, which show how self-assembly can build upon a genetic basis to give rise to the fundamental pollen exine structure. This paper is a synthesis of a new concept and a detailed review of achievements in the field of developmental palynology. It seeks to link what is known regarding development with the liquid crystal realm of colloid chemistry. 相似文献
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We performed dissipative particle dynamics (DPD) simulations to reproduce phase separation morphologies of diblock copolymers for directed self-assembly (DSA) lithography. DSA is a promising technique to overcome the current photolithography resolution limit. The Flory–Huggins χ parameter estimated from a small-angle X-ray scattering experiment was used for the DPD simulations owing to the multiple degrees of coarse-graining. The degree of coarse-graining and the bond parameter for the spring force were optimised to represent the experimental result of the number of lamellar layers formed in a trench guide. The DPD simulations using these parameters can also represent the diameter of the central cylinder domain that is formed by phase separation in the cylindrical hole. It was found that the bond parameter considering the spreading of polymer segments in a coarse-grained particle gives good quantitative agreement between the results of the simulations and the experimental data. 相似文献
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We have studied the ontogeny of the pollen wall of Hypecoum imberbe. Our initial observations with conventional transmission electron microscopy (TEM) were inconclusive due to the similarities found in the electrodensity of the foot layer and the endexine, and between this latter layer and the intine. Thus we applied the PTA acetone histochemical test in order to differentiate between the cell wall components. This method proved to be efficient in resolving the differences between the layers and even allowed us to distinguish two strata within the narrow intine layer. A thin foot layer can be distinguished only by the temporary presence of a single white line separating it from the initial deposition of the endexine. The aperture consists of two colpi with no special differentiation. The tapetum is a typical secretory type giving rise to elaioplasts and tapetosomes during development, which persist as individual organelles upon the degradation of the tapetum. As the ultrastructural organisation of the sporoderm seems to offer little protection to the gametophyte, we finally discuss how the structure of the pollen sporoderm might be related to the special morphological characteristics of a flower, its habitat, and the biology of the plant as a whole. 相似文献
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Although extremely low frequency (ELF) magnetic fields (<300 Hz) appear to exert a variety of biological effects, the magnetic field sensing/transduction mechanism(s) remains to be established. Here, using the inhibitory effects of magnetic fields on endogenous opioid peptide-mediated “analgaesic” response of the land snail. Cepaea nemoralis, we addressed the mechanism(s) of action of ELF magnetic fields. Indirect mechanisms involving both induced electric fields and direct magnetic field detection mechanisms (e.g., magnetite, parametric resonance) were evaluated. Snails were exposed to a static magnetic field (BDC=78±1 μT) and to a 60 Hz magnetic field (BAC=299±1 μT peak) with the angle between the static and 60 Hz magnetic fields varied in eight steps between 0° and 90°. At 0° and 90°, the magnetic field reduced opioid-induced analgaesia by approximately 20%, and this inhibition was increased to a maximum of 50% when the angle was between 50° and 70°. Because BAC was fixed in amplitude, direction, and frequency, any induced electric currents would be constant independent of the BAC/BDC angle. Also, an energy transduction mechanism involving magnetite should show greatest sensitivity at 90°. Therefore, the energy transduction mechanism probably does not involve induced electric currents or magnetite. Rather, our results suggest a direct magnetic field detection mechanism consistent with the parametric resonance model proposed by Lednev. © 1996 Wiley-Liss, Inc. 相似文献
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ALAN R. HEMSLEY F.L.S. 《Botanical journal of the Linnean Society. Linnean Society of London》1997,125(1):1-24
Abnormal megaspore tetrad configurations from Selaginella laevigata and of Lagenicula crass-iaculeata (Lower Carboniferous) have been studied by SEM. These abnormalities reflect the variation expected in the presumed evolution of the seed-plants from free-sporing het-erosporous ancestors. In addition, they indicate a possible role for the aborted members of a tetrad in the successful development and maturation of the functional spore(s). Aborted members of tetrads also reveal the later stages of the developmental sequence occurring in spore wall construction and highlight the interplay of sporopollenin production, its colloidal flocculation and polymerization, and distortion caused by protoplast expansion. Possible causes of abortion in both living and extinct lycopsid megaspores are discussed. 相似文献
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Dong X Hong Z Sivaramakrishnan M Mahfouz M Verma DP 《The Plant journal : for cell and molecular biology》2005,42(3):315-328
Callose (beta-1,3-glucan) is produced at different locations in response to biotic and abiotic cues. Arabidopsis contains 12 genes encoding callose synthase (CalS). We demonstrate that one of these genes, CalS5, encodes a callose synthase which is responsible for the synthesis of callose deposited at the primary cell wall of meiocytes, tetrads and microspores, and the expression of this gene is essential for exine formation in pollen wall. CalS5 encodes a transmembrane protein of 1923 amino acid residues with a molecular mass of 220 kDa. Knockout mutations of the CalS5 gene by T-DNA insertion resulted in a severe reduction in fertility. The reduced fertility in the cals5 mutants is attributed to the degeneration of microspores. However, megagametogenesis is not affected and the female gametes are completely fertile in cals5 mutants. The CalS5 gene is also expressed in other organs with the highest expression in meiocytes, tetrads, microspores and mature pollen. Callose deposition in the cals5 mutant was nearly completely lacking, suggesting that this gene is essential for the synthesis of callose in these tissues. As a result, the pollen exine wall was not formed properly, affecting the baculae and tectum structure and tryphine was deposited randomly as globular structures. These data suggest that callose synthesis has a vital function in building a properly sculpted exine, the integrity of which is essential for pollen viability. 相似文献
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细胞内生物大分子的相分离(Phaseseparation)现象是近几年受到极大关注的新兴研究领域。作为一种细胞生化反应的聚集分割机制,其在自然界中广泛存在,参与基因转录调控,影响生物体对外界刺激的应答等重要生理过程。相分离失调可能导致一些重大疾病的发生,诸多交叉领域的研究者正试图通过相分离这个全新角度来审视老年痴呆等相关疾病,探索其发生的分子机制以及通过相分离进行干预和治疗的潜在可能性。文中拟介绍该领域最新研究进展,从生物相分离现象的发现、生化基础及其与疾病发生的联系等方面,综述目前的主要研究方向,并对该领域拟解决的关键问题进行展望。 相似文献
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Jose J. Ordaz-Ortiz Susan E. Marcus J. Paul Knox 《植物生理学报》2009,(5):910-921
Methods developed to isolate intact cells from both unripe and ripe tomato fruit pericarp parenchyma have allowed the cell biological analysis of polysaccharide epitopes at the surface of separated cells. The LM7 pectic homogalacturonan epitope is a marker of the junctions of adhesion planes and intercellular spaces in parenchyma systems. The LM7 epitope persistently marked the former edge of adhesion planes at the surface of cells separated from unripe and ripened tomato fruit and also from fruits with the Cnr mutation. The LM 11 xylan epitope was associated, in sections, with cell walls lining intercellular space but the epitope was not detected at the surface of isolated cells, being lost during cell isolation. The LM15 xyloglucan epitope was present at the surface of cells isolated from unripe fruit in a pattern reflecting the former edge of cell adhesion planes/intercellular space but with gaps and apparent breaks. An equivalent pattern of LM15 epitope occurrence was revealed at the surface of cells isolated by pectate lyase action but was not present in cells isolated from ripe fruit or from Cnr fruit. In contrast to wild-type cells, the LM5 galactan and LM21 mannan epitopes occurred predominantly in positions reflecting intercellular space in Cnr, suggesting a concerted alteration in cell wall microstructure in response to this mutation. Galactanase and mannanase, along with pectic homogalacturonan-degrading enzymes, were capable of releasing cells from unripe fruit parenchyma. These observations indicate that hemicellulose polymers are present in architectural contexts reflecting cell adhesion and that several cell wall polysaccharide classes are likely to contribute to cell adhesion/cell separation in tomato fruit pericarp parenchyma. 相似文献
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Pollen wall development in flowering plants 总被引：7，自引：0，他引：7
The outer pollen wall, or exine, is more structurally complex than any other plant cell wall, comprising several distinct layers, each with its own organizational pattern. Since elucidation of the basic events of pollen wall ontogeny using electron microscopy in the 1970s, knowledge of their developmental genetics has increased enormously. However, self-assembly processes that are not under direct genetic control also play an important role in pollen wall patterning. This review integrates ultrastructural and developmental findings with recent models for self-assembly in an attempt to understand the origins of the morphological complexity and diversity that underpin the science of palynology. 相似文献
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BACKGROUND AND AIMS: Early developmental events in microsporogenesis are known to play a role in pollen morphology: variation in cytokinesis type, cell wall formation, tetrad shape and aperture polarity are responsible for pollen aperture patterning. Despite the existence of other morphologies, monosulcate pollen is one of the most common aperture types in monocots, and is also considered as the ancestral condition in this group. It is known to occur from either a successive or a simultaneous cytokinesis. In the present study, the developmental sequence of microsporogenesis is investigated in several species of Asparagales that produce such monosulcate pollen, representing most families of this important monocot clade. METHODS: The developmental pathway of microsporogenesis was investigated using light transmission and epifluorescence microscopy for all species studied. Confocal microscopy was used to confirm centripetal cell plate formation. KEY RESULTS: Microsporogenesis is diverse in Asparagales, and most variation is generally found between families. It is confirmed that the whole higher Asparagales clade has a very conserved microsporogenesis, with a successive cytokinesis and centrifugal cell plate formation. Centripetal cell wall formation is described in Tecophilaeaceae and Iridaceae, a feature that had so far only been reported for eudicots. CONCLUSIONS: Monosulcate pollen can be obtained from several developmental pathways, leading thus to homoplasy in the monosulcate character state. Monosulcate pollen should not therefore be considered as the ancestral state unless it is produced through the ancestral developmental pathway. The question about the ancestral developmental pathway leading to monosulcy remains open. 相似文献
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Developing scaffolds that mimic the architecture of tissue at the nanoscale is one of the major challenges in the field of tissue engineering. The development of nanofibers has greatly enhanced the scope for fabricating scaffolds that can potentially meet this challenge. Currently, there are three techniques available for the synthesis of nanofibers: electrospinning, self-assembly, and phase separation. Of these techniques, electrospinning is the most widely studied technique and has also demonstrated the most promising results in terms of tissue engineering applications. The availability of a wide range of natural and synthetic biomaterials has broadened the scope for development of nanofibrous scaffolds, especially using the electrospinning technique. The three dimensional synthetic biodegradable scaffolds designed using nanofibers serve as an excellent framework for cell adhesion, proliferation, and differentiation. Therefore, nanofibers, irrespective of their method of synthesis, have been used as scaffolds for musculoskeletal tissue engineering (including bone, cartilage, ligament, and skeletal muscle), skin tissue engineering, vascular tissue engineering, neural tissue engineering, and as carriers for the controlled delivery of drugs, proteins, and DNA. This review summarizes the currently available techniques for nanofiber synthesis and discusses the use of nanofibers in tissue engineering and drug delivery applications. 相似文献
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N. R. Meychik A. V. Smirnova N. P. Matveeva Yu. I. Nikolaeva I. P. Ermakov 《Russian Journal of Plant Physiology》2009,56(2):211-218
Changes in the composition of ionogenic groups of the polymeric matrix of the cell walls of lily (Lilium longiflorum Thunb.) pollen grains were studied during its activation at the early stages of pollen germination. In the cell walls isolated from nonactivated and activated pollen grains, four types of ionogenic groups were identified: amino groups, carboxylic groups of uronic acids, phenolic OH-groups. and groups with pKa 7–8. During the early stages of germination, ionization constants of each type groups remained unchanged, but the quantitative composition of ionogenic groups in the intine changed. In this matrix, a decrease in the content of phenolic groups and demethylated carboxylic groups of uronic acids was detected. It is supposed that, at early stages of germination, the intine loses some part of acid pectins and some phenolic compounds. 相似文献
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Biomolecular condensation, driven by multivalency, serves as a fundamental mechanism within cells, facilitating the formation of distinct compartments, including membraneless organelles that play essential roles in various cellular processes. Perturbations in the delicate equilibrium of condensation, whether resulting in gain or loss of phase separation, have robustly been associated with cellular dysfunction and physiological disorders. As ongoing research endeavors wholeheartedly embrace this newly acknowledged principle, a transformative shift is occurring in our comprehension of disease. Consequently, significant strides have been made in unraveling the profound relevance and potential causal connections between abnormal phase separation and various diseases. This comprehensive review presents compelling recent evidence that highlight the intricate associations between aberrant phase separation and neurodegenerative diseases, cancers, and infectious diseases. Additionally, we provide a succinct summary of current efforts and propose innovative solutions for the development of potential therapeutics to combat the pathological consequences attributed to aberrant phase separation. 相似文献
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Michael S. Zavada 《Plant Systematics and Evolution》1984,147(1-2):63-78
In angiosperm pollen the reticulate-perforate exine sculpturing is associated with sporophytic self-incompatibility (S.S.I.) and imperforate and microperforate exine sculpturing is associated with gametophytic self-incompatibility. The earliest unequivocal angiosperm pollen conforms to exine morphology of pollen from plants with S.S.I. The orgin of S.S.I. is hypothesized to have coincided with the appearance of what is now the earliest recognizable angiosperm pollen. Other angiosperm characteristics correlated with S.I., functional stigmatic areas, large showy flowers (or aggregated inflorescences), and passive seed dispersal, provide some insight into the biological aspects of the earliest angiosperms. 相似文献
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Javier Sampedro Mara Guttman Lian‐Chao Li Daniel J. Cosgrove 《The Plant journal : for cell and molecular biology》2015,81(1):108-120
Expansins are wall‐loosening proteins that promote the extension of primary cell walls without the hydrolysis of major structural components. Previously, proteins from the EXPA (α–expansin) family were found to loosen eudicot cell walls but to be less effective on grass cell walls, whereas the reverse pattern was found for EXPB (β–expansin) proteins obtained from grass pollen. To understand the evolutionary and structural bases for the selectivity of EXPB action, we assessed the extension (creep) response of cell walls from diverse monocot families to EXPA and EXPB treatments. Cell walls from Cyperaceae and Juncaceae (families closely related to grasses) displayed a typical grass response (‘β–response’). Walls from more distant monocots, including some species that share with grasses high levels of arabinoxylan, responded preferentially to α–expansins (‘α–response’), behaving in this regard like eudicots. An expansin with selective activity for grass cell walls was detected in Cyperaceae pollen, coinciding with the expression of genes from the divergent EXPB–I branch that includes grass pollen β–expansins. The evolutionary origin of this branch was located within Poales on the basis of phylogenetic analyses and its association with the ‘sigma’ whole‐genome duplication. Accelerated evolution in this branch has remodeled the protein surface in contact with the substrate, potentially for binding highly substituted arabinoxylan. We propose that the evolution of the divergent EXPB–I group made a fundamental change in the target and mechanism of wall loosening in the grass lineage possible, involving a new structural role for xylans and the expansins that target them. 相似文献