Follicular cells of the amphibian ovary: Origin, structure, and functions

Formation of the follicular envelopes surrounding oocytes in the developing ovary and their subsequent morphological differentiation go hand-in-hand with succession of the steroidogenesis stages, arrest of meiosis and its maintenance, establishment of the conditions necessary for vitellogenesis, oocyte growth, and maturation. Metabolites are exchanged via gap junctions and receptor-mediated transport through the perioocytic space. The ion transport in follicular cells (FCs) regulates the plasma membrane potential, creating the conditions for efficient directed transport through gap junctions. Manifold biologically active substances accepted by follicular cells are an additional adjusting lever for regulating the state of follicle system. In this review, we have attempted to emphasize the amphibian FCs as key players in the follicle system; the more so as we have failed to find any review that would bring together the data on the origin of amphibian FCs, their morphology, as well as regulation of oocyte growth and development. As a rule, recent works in this field focus on the molecular mechanisms providing for regulation of individual stages in oocyte development. This review describes the origin and changes in the morphology of follicular cells during the development of Xenopus laevis oocyte as well as the data on their regulatory functions in vitellogenesis and their involvement in steroidogenesis, maintenance of meiotic arrest, and subsequent maturation.     

The plant cell wall: Biosynthesis,construction, and functions

The plant cell wall is composed of multiple biopolymers, representing one of the most complex structural networks in nature. Hundreds of genes are involved in building such a natural masterpiece. However, the plant cell wall is the least understood cellular structure in plants. Due to great progress in plant functional genomics,manyachievementshavebeenmadein uncovering cell wall biosynthesis, assembly, and architecture, as well as cell wall regulation and signaling. Such information has significantly advanced our understanding of the roles of the cell wall in many biological and physiological processes and has enhanced our utilization of cell wall materials. The use of cutting-edge technologies such as single-molecule imaging,nuclear magnetic resonance spectroscopy, and atomic force microscopy has provided much insight into the plant cell wall as an intricate nanoscale network, opening up unprecedented possibilities for cell wall research. In this review,we summarize the major advances made in understanding the cell wall in this era of functional genomics, including the latest findings on the biosynthesis, construction, and functions of the cell wall.     

The plant glutathione transferase gene family: genomic structure, functions, expression and evolution

Glutathione transferases (GSTs) are ubiquitous, multifunctional proteins encoded by large gene families. In different plant species this gene family is comprised of 25–60 members, that can be grouped into six classes on the basis of sequence identity, gene organization and active site residues in the protein. The Phi and Tau classes are the most represented and are plant specific, while Zeta and Theta GSTs are found also in animals. Despite pronounced sequence and functional diversification, GSTs have maintained a highly conserved three-dimensional structure through evolution. Most GSTs are cytosolic and active as dimers, performing diverse catalytic as well as non-catalytic roles in detoxification of xenobiotics, prevention of oxidative damage and endogenous metabolism. Among their catalytic activities are the conjugation of electrophilic substrates to glutathione, glutathione-dependent isomerizations and reductions of toxic organic hydroperoxides. Their main non-catalytic role is as hormone and flavonoid ligandins. GST genes are predominantly organized in clusters non-randomly distributed in the genome. Phylogenetic studies indicate that plant GSTs have mainly evolved after the divergence of plants, the two prevalent Phi and Tau classes being the result of recent, multiple duplication events.     

Aminoglycoside antibiotics: structure, functions and effects on in vitro plant culture and genetic transformation protocols

Plant transformation protocols generally involve the use of selectable marker genes for the screening of transgenic material. The bacterial gene nptII, coding for a neomycin phosphotransferase, and the hpt gene, coding for a hygromycin phosphotransferase, are frequently used. These enzymes detoxify aminoglycoside antibiotics by phosphorylation, thereby permitting cell growth in the presence of antibiotics. Nevertheless, the screening for transgenic regenerated shoots is often partial and difficult due to regeneration of escapes and chimeras. These difficulties can be caused, in part, by an incorrect assumption about the mode of action of antibiotics in bacterial and eukaryotic cells and in in vitro tissue culture. The information contained in this review could be useful to establish better selection strategies by taking into account factors such as explant complexity, transformation and selection protocols that allow better accessibility to cells of Agrobacterium and antibiotics, and faster regeneration methods that avoid collateral effects of antibiotics on recovered, putative transgenic shoots.     

Physiological functions of plant cell coverings

The cell coverings of plants have two important functions in plant life. Plant cell coverings are deeply involved in the regulation of the life cycle of plants: each stage of the life cycle, such as germination, vegetative growth, reproductive growth, and senescence, is strongly influenced by the nature of the cell coverings. Also, the apoplast, which consists of the cell coverings, is the field where plant cells first encounter the outer environment, and so becomes the major site of plant responses to the environment. In the regulation of each stage of the life cycle and the response to each environmental signal, some specific constituents of the cell coverings, such as xyloglucans in dicotyledons and 1,3,1,4-β-glucans in Gramineae, act as the key component. The physiological functions of plant cell coverings are sustained by the metabolic turnover of these components. The components of the cell coverings are supplied from the symplast, but then they are modified or degraded in the apoplast. Thus, the metabolism of the cell coverings is regulated through the cross-talk between the symplast and the apoplast. The understanding of physiological functions of plant cell coverings will be greatly advanced by the use of genomic approaches. At the same time, we need to introduce nanobiological techniques for clarifying the minute changes in the cell coverings that occur in a small part within each cell. Electronic Publication     

Virtual issue: cell wall functions in plant growth and environmental responses

Journal of Plant Research - Plant cell walls have multiple functions, including determining cell shape and size, cell–cell adhesion, controlling cell differentiation and growth, and promoting...     

植物GRAS蛋白结构和功能研究进展

GRAS蛋白是一类植物特有的蛋白家族,是许多重要生长发育过程中的关键调控蛋白,如赤霉素信号转导、光信号转导、根的发育、根瘤和菌根形成以及分生组织形成等。从蛋白分子结构、分类及生理功能等方面综述了植物GRAS蛋白的最新研究进展,并对未来的研究方向进行了讨论。     

The nuclear envelope in the plant cell cycle: structure, function and regulation

Background

Higher plants are, like animals, organisms in which successful completion of the cell cycle requires the breakdown and reformation of the nuclear envelope in a highly controlled manner. Interestingly, however, while the structures and processes appear similar, there are remarkable differences in protein composition and function between plants and animals.

Scope

Recent characterization of integral and associated components of the plant nuclear envelope has been instrumental in understanding its functions and behaviour. It is clear that protein interactions at the nuclear envelope are central to many processes in interphase and dividing cells and that the nuclear envelope has a key role in structural and regulatory events.

Conclusion

Dissecting the mechanisms of nuclear envelope breakdown and reformation in plants is necessary before a better understanding of the functions of nuclear envelope components during the cell cycle can be gained.     

Stromules: Mobile Protrusions and Interconnections Between Plastids

Abstract: Stroma-filled tubules, recently named stromules, extend from the surface of plastids in most cell types and plant species examined. Stromules are highly dynamic structures, continuously and rapidly changing shape. They have been shown to interconnect plastids and permit the exchange of green fluorescent protein (GFP) between plastids. Stromules are enclosed by the inner and outer plastid envelope membranes and are 0.4 - 0.8 μm in diameter and up to 65 μm long. Movement of stromules is dependent on the actin cytoskeleton and the ATPase activity of myosin. Stromules are more abundant in cells containing a relatively small plastid volume and provide a means of enormously increasing the plastid surface area. Many important questions on the structure, function and mobility of stromules remain unanswered.     

Ankyrin: structure, properties, and functions

Recent data on characteristics of the structure, functions, and main properties of ankyrins (proteins that are linkers between the spectrin-based cytoskeleton and integral membrane proteins) are summarized. The interactions of ankyrins with band-3 protein, P-type ATPases, ion channels, receptors, and protein kinase C are considered. The structure of ankyrin repeats that are often contained in other proteins (which are not classified with the ankyrin family) and ensure protein-protein interactions as well as interactions between proteins and nucleic acids is described in details. The mechanisms of regulation of the ability of ankyrins to interact with other proteins (alternative splicing and post-translational modification, including phosphorylation) are also considered.     

Stromules: a characteristic cell-specific feature of plastid morphology

Stromules (stroma-filled tubules) are highly dynamic structures extending from the surface of all plastid types examined so far, including proplastids, chloroplasts, etioplasts, leucoplasts, amyloplasts, and chromoplasts. Stromules are usually 0.35-0.85 microm in diameter and of variable length, from short beak-like projections to linear or branched structures up to 220 mum long. They are enclosed by the inner and outer plastid envelope membranes and enable the transfer of molecules as large as Rubisco (approximately 560 kDa) between interconnected plastids. Stromules occur in all cell types, but stromule morphology and the proportion of plastids with stromules vary from tissue to tissue and at different stages of plant development. In general, stromules are more abundant in tissues containing non-green plastids, and in cells containing smaller plastids. The primary function of stromules is still unresolved, although the presence of stromules markedly increases the plastid surface area, potentially increasing transport to and from the cytosol. Other functions of stromules, such as transfer of macromolecules between plastids and starch granule formation in cereal endosperm, may be restricted to particular tissues and cell types.     

The plant microbiota: composition,functions, and engineering

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Long-wavelength chlorophylls in photosystem I of cyanobacteria: Origin,localization, and functions

The structural organization of photosystem I (PSI) complexes in cyanobacteria and the origin of the PSI antenna long-wavelength chlorophylls and their role in energy migration, charge separation, and dissipation of excess absorbed energy are discussed. The PSI complex in cyanobacterial membranes is organized preferentially as a trimer with the core antenna enriched with long-wavelength chlorophylls. The contents of long-wavelength chlorophylls and their spectral characteristics in PSI trimers and monomers are species-specific. Chlorophyll aggregates in PSI antenna are potential candidates for the role of the long-wavelength chlorophylls. The red-most chlorophylls in PSI trimers of the cyanobacteria Arthrospira platensis and Thermosynechococcus elongatus can be formed as a result of interaction of pigments peripherally localized on different monomeric complexes within the PSI trimers. Long-wavelength chlorophylls affect weakly energy equilibration within the heterogeneous PSI antenna, but they significantly delay energy trapping by P700. When the reaction center is open, energy absorbed by long-wavelength chlorophylls migrates to P700 at physiological temperatures, causing its oxidation. When the PSI reaction center is closed, the P700 cation radical or P700 triplet state (depending on the P700 redox state and the PSI acceptor side cofactors) efficiently quench the fluorescence of the long-wavelength chlorophylls of PSI and thus protect the complex against photodestruction.     

Ionophorous functions of phosphatidic acid in the plant cell

Effects of phosphatidic acid (PA), a product of phospholipase D activity, on Ca²⁺ and H⁺ transport were investigated in membrane vesicles obtained from roots and coleoptiles of maize (Zea mays L.). Calcium flows were measured with fluorescent probes indo-1 and chlorotetracycline loaded into the vesicles and added to the incubation medium, respectively. Phosphatidic acid (50–500 μM) was found to induce downhill flow of Ca²⁺ along the concentration gradient into the plasma membrane vesicles and endomembrane vesicles (tonoplast and endoplasmic reticulum). Protonophorous functions of PA were probed with acridine orange. First, the ionic H⁺ gradient was created on the tonoplast vesicles by means of H⁺-ATPase activation with Mg-ATP addition. Then, the vesicles were treated with 25–100 μM PA, which induced the release of protons from tonoplast vesicles and dissipation of the proton gradient. Thus, PA could function as an ionophore and was able to transfer Ca²⁺ and H⁺ across plant cell membranes along concentration gradients of these ions. The role of PA in mechanisms of intracellular signaling in plants is discussed.     

Cycling in a crowd: Coordination of plant cell division,growth, and cell fate

The reiterative organogenesis that drives plant growth relies on the constant production of new cells, which remain encased by interconnected cell walls. For these reasons, plant morphogenesis strictly depends on the rate and orientation of both cell division and cell growth. Important progress has been made in recent years in understanding how cell cycle progression and the orientation of cell divisions are coordinated with cell and organ growth and with the acquisition of specialized cell fates. We review basic concepts and players in plant cell cycle and division, and then focus on their links to growth-related cues, such as metabolic state, cell size, cell geometry, and cell mechanics, and on how cell cycle progression and cell division are linked to specific cell fates. The retinoblastoma pathway has emerged as a major player in the coordination of the cell cycle with both growth and cell identity, while microtubule dynamics are central in the coordination of oriented cell divisions. Future challenges include clarifying feedbacks between growth and cell cycle progression, revealing the molecular basis of cell division orientation in response to mechanical and chemical signals, and probing the links between cell fate changes and chromatin dynamics during the cell cycle.

Plant cell cycle and division are linked to specific cell fates and respond to growth-related cues, such as metabolic state, cell size, cell shape, and mechanical stress.