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41.
Olga A. Romanova Timur H. Tenchurin Tatiana S. Demina Elena V. Sytina Alexey D. Shepelev Stanislav G. Rudyak Olga I. Klein Sergey V. Krasheninnikov Elizaveta I. Safronova Roman A. Kamyshinsky Vissarion G. Mamagulashvili Tatiana A. Akopova Sergey N. Chvalun Andrey A. Panteleyev 《Cell proliferation》2019,52(3)
42.
Krichevsky A Kozlovsky SV Tian GW Chen MH Zaltsman A Citovsky V 《Developmental biology》2007,303(2):405-420
Sexual reproduction of flowering plants depends on delivery of the sperm to the egg, which occurs through a long, polarized projection of a pollen cell, called the pollen tube. The pollen tube grows exclusively at its tip, and this growth is distinguished by very fast rates and reaches extended lengths. Thus, one of the most fascinating aspects of pollen biology is the question of how enough cell wall material is produced to accommodate such rapid extension of pollen tube, and how the cell wall deposition and structure are regulated to allow for rapid changes in the direction of growth. This review discusses recent advances in our understanding of the mechanism of pollen tube growth, focusing on such basic cellular processes as control of cell shape and growth by a network of cell wall-modifying enzymes, molecular motor-mediated vesicular transport, and intracellular signaling by localized gradients of second messengers. 相似文献
43.
The attachment ability of insects on surfaces are associated not only with the micro- and nanostructure of the adhering part
of an attachment device, but also with the global scale kinematics responsible for contact formation and release. In the present
study, the locomotory techniques of several representatives of insects from four different orders (Orthoptera, Heteroptera,
Coleoptera, and Hymenoptera), possessing different types of attachment structures, are described. The study is based on video
recordings of insects walking on a flat surface and on cylindrical rods of various thickness, imitating plant stems. Attachment
devices of tarsi and pretarsi were visualized using Scanning Electron Microscopy. The results show a different manner in the
use of adhesive structures on substrates with various curvatures. Insects bearing attachment pads on proximal tarsomeres usually
touch flat and curved substrates using all tarsomeres, whereas insects with their attachment devices on the distal tarsomeres
usually walk on flat surfaces using the distal tarsomeres of the overextended tarsus. On substrates, with diameters comparable
to or larger than the tarsus length, insects walk above the stem by clasping the stem with the bent tarsi. On thin stems,
insects clasp the stem between their tarsi and hang under the stem. Thus, on thin and thick rods, forces applied to attachment
organs act in opposite directions. There are two methods of leg positioning for walking on a rough flat substrate. In the
first case, the tarsus is straightened and the rough substrate is gripped between the claws and the proximal complex of attachment
devices (tarsal euplantulae, fossulae spongiosa, and terminal spurs of tibiae). In the second case the tibia does not touch
the substrate; the insect is supported only by distal tarsomeres. The tarsus is in an overextended condition. On rods, with
diameters comparable to or larger than the tarsus length, insects walk by clasping the stem with the bent tarsi. This posture
is characteristic for the majority of insects independent of the tarsal position they normally use while walking on a plane.
If the rod’s diameter is smaller than the tarsus length, walking insects usually clutch it between contralateral tarsi. Using
such a posture they are supported by interlocking or by strong friction, generated by attachment devices of the proximal tarsomeres,
and do not use attachment devices of the pretarsus. Contact with the substrate is reinforced due to the coordinated contralateral
clutch using all supporting legs. It is concluded that the use of different types of attachment structures correlates with
locomotory techniques.
Handling Editor: Heikki Hokkanen 相似文献
44.
Physicochemical models of signaling pathways are characterized by high levels of structural and parametric uncertainty, reflecting both incomplete knowledge about signal transduction and the intrinsic variability of cellular processes. As a result, these models try to predict the dynamics of systems with tens or even hundreds of free parameters. At this level of uncertainty, model analysis should emphasize statistics of systems-level properties, rather than the detailed structure of solutions or boundaries separating different dynamic regimes. Based on the combination of random parameter search and continuation algorithms, we developed a methodology for the statistical analysis of mechanistic signaling models. In applying it to the well-studied MAPK cascade model, we discovered a large region of oscillations and explained their emergence from single-stage bistability. The surprising abundance of strongly nonlinear (oscillatory and bistable) input/output maps revealed by our analysis may be one of the reasons why the MAPK cascade in vivo is embedded in more complex regulatory structures. We argue that this type of analysis should accompany nonlinear multiparameter studies of stationary as well as transient features in network dynamics. 相似文献
45.
46.
Stratilová Barbora Firáková Zuzana Klaudiny Jaroslav Šesták Sergej Kozmon Stanislav Strouhalová Dana Garajová Soňa Ait-Mohand Fairouz Horváthová Ágnes Farkaš Vladimír Stratilová Eva Hrmova Maria 《Plant molecular biology》2019,100(1-2):181-197
Plant Molecular Biology - The knowledge of substrate specificity of XET enzymes is important for the general understanding of metabolic pathways to challenge the established notion that these... 相似文献
47.
Ginkgolides A, B, C and J, together with bilobalide, are unique terpenoid components of the Ginkgo biloba tree. Due to similar chemical properties, their separation is quite tedious. We have developed an efficient and rapid protocol for separation of individual ginkgolides and bilobalide from G. biloba extracts. The procedure takes advantage of enhanced susceptibility of ginkgolides B and C to benzylation and the ease of separation of these products from ginkgolides A and J which do not react. The protocol is applicable to the previously reported enriched extracts prepared from G. biloba leaves. A single chromatographic step prior to benzylation provides bilobalide and mixture of ginkgolides A, B, C, and J. After benzylation, the individual ginkgolides are separated by chromatography. 相似文献
48.
MHC class I molecules are heterotrimeric complexes composed of heavy chain, 2-microglobulin (2m) and short peptide. This trimeric complex is generated in the endoplasmic reticulum (ER), where a peptide loading complex (PLC) facilitates transport from the cytosol and binding of the peptide to the preassembled ER resident heavy chain/2m dimers. Association of mouse MHC class I heavy chain with 2m is characterized by allelic differences in the number and/or positions of amino acid interactions. It is unclear, however, whether all alleles follow common binding patterns with minimal contributions by allele-specific contacts, or whether essential contacts with 2m are different for each allele. While searching for the PLC binding site in the 3 domain of the mouse MHC class I molecule H-2Db, we unexpectedly discovered a site critical for binding mouse, but not human, 2m. Interestingly, amino acids in the corresponding region of another MHC class I heavy chain allele do not make contacts with the mouse 2m. Thus, there are allelic differences in the modes of binding of 2m to the heavy chain of MHC class I. 相似文献
49.
We experimentally demonstrated the ability of three short-lived monocarpic species to vegetatively regenerate (resprout) from
roots after severe disturbance. We assessed the relationship between resprouting ability and (1) timing of injury with respect
to life-cycle stage (reproductive vs. vegetative plant), life-history mode (annual vs. winter annual) and phenological stage
(flowering vs. fruiting plant), (2) nutrient availability, and (3) disturbance severity (removal of all axillary buds Yes/No).
In a chamber experiment with the annual or potentially winter annualRorippa palustris, all injured plants resprouted in all nutrient levels and day-length regimes (day-length regimes simulated conditions of
an annual and a winter annual cohort). The number of adventitious buds on roots was positively affected only by injury. The
extent of regeneration and amount of regenerated biomass were higher at high nutrient level and long-day regime. 相似文献
50.
Gorb SN 《Arthropod Structure & Development》2004,33(3):201-220
In Auchenorrhyncha, jumping is achieved by metathoracic muscles which are inserted into the trochanter of the hind leg. The synchronisation of movements of the hind legs is a difficult problem, as the leg extension that produces the jump occurs in less than 1 ms. Even slight asynchrony could potentially result in failure of a jump. Both the synchronisation of the movements of a pair of jumping legs, and their stabilisation during a jump, seem to be important problems for small jumping insects. The present study was performed in order to clarify some questions of the functional morphology of the leafhopper jumping mechanism. It is based on skeleton-muscle reconstruction, high-speed video recordings, transmission (TEM) and scanning electron microscopic (SEM) investigations of the cuticle, together with 3D inverse-kinematic modelling of angles and working zones of hind leg joints of cicada Cercopis vulnerata (Cercopidae). The complete extension of the hind leg takes less than 1 ms, which suggests that the jump is powered not only by the muscle system, but also by an elastic spring. Histological staining and fluorescence microscopy showed resilin-bearing structures, responsible for elastic energy storage, in the pleural area of the metathorax. Synchronisation of hind leg movements may be aided by microtrichia fields that are located on the medial surface of each hind coxa. In Auchenorrhyncha, hind coxae are rounded in their anterior and lateral parts, whereas medial parts are planar, and contact each other over a rather large area. The inverse-kinematic model of propulsive leg movements was used to draw the surface outlined by the medial surface of the coxa, during the jump movement. This is a cone surface, faced with its bulged-in side, medially. Surfaces outlined by the movements of both right and left coxae overlap in their anterior and posterior positions. In both extreme positions, coxae are presumably connected to each other by coupled microtrichia fields. Thus, in extreme positions, both coxae can be moved synchronously. 相似文献