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  • 1
    ISSN: 1615-6102
    Keywords: Chromatin condensation ; DNA content ; Nuclear size ; Root apex ; Root tissues ; Zea mays L
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Nuclei of various tissues exhibit different structure in the maize root apex. Moreover, the nuclear structure is in close correlation with the DNA and RNA synthesis. These observations are in contradiction with the hypothesis according to which the chromatin organization in plant nuclei is species-specific and does not correspond to the metabolic activity of nuclei. The possible reasons for this disagreement are discussed. The extended state of chromatin is not the passive result of synthetic processes in the nucleus, but, on the contrary, it is one of the primary factors which are indispensable for the DNA transcription. Results presented here together with data from literature suggest that the organization of chromatin complex appears as a general control mechanism which determines the efficiency of other more specific mechanisms.
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  • 2
    ISSN: 1615-6102
    Keywords: Arabinogalactan proteins ; Maize ; Phloem ; Root
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The cell-specific expression of two arabinogalactan protein (AGP) epitopes recognized by monoclonal antibodies JIM8 and JIM13 is reported in maize roots. Employing immunofluorescence and immunogold electron microscopy, the JIM8 antibody was shown to label exclusively protophloem sieve elements, while the JIM13 antibody labelled sieve elements very strongly and adjacent pericycle and companion cells, as well as sloughing root cap cells less strongly. Since the labelling of sieve elements with JIM8 antibody was specific and did not spread to other cell types during root development, it is concluded that this AGP epitope can serve as a specific marker of these specialized cells within the maize root. In the case of the AGP epitope recognized by JIM13 antibody, part of the immunofluorescence label was also found to be associated with cytoplasmic strands in the pericycle and sloughing root cap cells. Immunogold-labelling of sieve elements revealed the association of both AGP epitopes (JIM8 and JIM13) with cortical sieve element reticulum and plasma membranes. Labelling of sieve element reticulum was prominent at its domains of adhesion to the plasma membrane, P-type plastids, and mitochondria. Based on our subcellular studies, we propose a new function of AGP epitopes in endomembrane recognition and adhesion within the sieve elements of maize roots.
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  • 3
    ISSN: 1615-6102
    Keywords: Actin ; Cadherin ; Catenin ; Endoplasmic-reticulum membrane ; Maize ; Root
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary With heterologous antibodies raised against animal N-cadherin, α-catenin, and β-catenin, we have visualized their reactive proteins within cells of maize root apices. Embedding using Steedman's wax allowed us to accomplish tissue-specific analysis which revealed that cells of epidermis, endodermis/pericycle, and outer stele tissues, all of which are tightly associated to each other, are especially enriched with presumed plant homologues of N-cadherin and both catenins. In the root epidermis, trichoblasts initiating root hairs showed prominent accumulations of cadherin-like antigens at outgrowing domains where they co-localize with actin. Close associations of cadherin-like proteins with F-actin were detected in parenchymatic cells of the stele, also at the immunogold electron microscopy level. A possible role of these interesting proteins in membrane-membrane interactions is indicated by their prominent accumulations at endoplasmic-reticulum-enriched pit-field-based plant cell adhesion domains in plasmolyzing cells of maize root apices exposed to mannitol. Intriguingly, these unique adhesion domains of plasmolyzing cells are enriched with endoplasmic-reticulum-resident calreticulin. Cadherin-like, but not catenin-like, proteins were abundant also within the nucleoplasm.
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  • 4
    ISSN: 1615-6102
    Keywords: Barley leaves ; Chromatin condensation ; Confocal microscopy ; Microtubules ; Nuclear events ; Ploidy levels ; Powdery mildew
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Post-mitotic epidermal cells of barley leaves were found to contain, in addition to cortical microtubules (CMTs), distinct arrays of endoplasmic microtubules (EMTs). These encircle nuclei and continuously merge into the CMT arrays that underly the plasmalemma. Detailed three-dimensional reconstruction of both types of MTs during fungal infection showed that profound and very rapid MT rearrangements occurred especially in the case of incompatible (resistant) barley-powdery mildew genotype combination. The most early MT responses, followed by their subsequent complete disintegration, were recorded around nuclei. These events might be relevant for the induction of such nuclear processes as onset of DNA synthesis and nuclear chromatin condensation. Observed pattern of early infection events, as well as less prominent responses in the case of compatible (susceptible) barley-powdery mildew genotype combination, both findings suggest that rapid reorganization of the MT cytoskeleton could be involved in recognition of the fungus by host cells and in the initiation of resistance responses in barley leaves. We hypothesize that the integrity and dynamics of the MT cytoskeleton, especially of its perinuclear part, might participate in control mechanisms involved in activation of resistance genes.
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  • 5
    ISSN: 1615-6102
    Keywords: Actin microfilaments ; Cell body ; Cell cycle ; Cell growth ; Cell polarity ; Microtubules
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Certain aspects of cellular behaviour in relation to growth and development of plants can be understood in terms of the “cell body” concept proposed by Daniel Mazia in 1993. During the interphase of the mitotic cell cycle, the plant cell body is held to consist of a nucleus and a perinuclear microtubule-organizing centre from which microtubules radiate into the cytoplasm. During mitosis and cytokinesis in meristematic cells, and also during the period of growth in post-mitotic cells immediately beyond the meristem, the plant cell body undergoes various characteristic morphological transformations, many of which are proposed as being related to changing structural connections with the actin-based component of the cytoskeleton and with specialized, plasma-membrane-associated sites at the cell periphery. In post-mitotic cells, these transformations of the plant cell body coincide with, and probably provide conditions for, the various pathways of development which such cells follow. They are also responsible, for the acquisition of new cellular polarities. Events in which the plant cell body participates include the formation of a mitotic spindle, phragmoplast, and new cell division wall, the rearrangement of a diffuse type of cell wall growth into tip growth (as occurs, e.g., during the initiation and subsequent development of root hairs), and the growth and division that occurs in reactivated vacuolate cells. If more evidence can be marshalled in support of the existence and properties of the plant cell body, then this concept could prove useful in interpreting the cytological bases of a range of developmental events in plants.
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  • 6
    ISSN: 1615-6102
    Keywords: Arabinogalactan protein ; Drosera capensis ; Endoplasmic reticulum ; Golgi apparatus ; Tonoplast ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Arabinogalactan proteins (AGPs) are proteoglycans detected in high amounts at plant cell surfaces; however, details of their subcellular localization are largely unknown. Immunolocalization studies with the anti-AGP monoclonal antibody LM2 have indicated that this AGP epitope is associated with secretory compartments such as endoplasmic reticulum and Golgi apparatus within plant cells actively producing and secreting AGPs. The LM2 epitope contains a β-linked glucuronic acid residue and occurs in the polysaccharide moiety of AGPs. We have localized this AGP epitope also to the tonoplast and to cytoplasmic strands. Endomembrane association of AGPs was confirmed with two other monoclonal antibodies, JIM13 and MAC207, both reacting with carbohydrate AGP epitopes containing GlcpA-β(1→3)-D-GalpA-α(1→2)-L-Rha residues. Immunocytochemistry is supported by biochemical analysis which shows that LM2 reacts with the microsomal fraction and also with low-molecular-weight material of the detergent phase after Triton X-114 phase separation prepared from maize roots. Our results indicate that some AGP epitopes are closely associated with endomembranes.
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  • 7
    ISSN: 1615-6102
    Keywords: Cold treatment ; Cytoskeleton ; Microtubules ; Roots ; Zea mays
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Microtubules (MTs) in cells of various tissues at different distances from the apex of the maize root exhibited different sensitivities to cold (5 °C), as judged by MT reorientation and tendency to depolymerization. Their responses seem to be related to their initial intracellular arrangements. Generally, MTs in cells which were ceasing elongation were the least sensitive during the early stages (6–24 h) of cold treatment, but during the later stages (5–7 d) MTs in most of these cells eventually depolymerized. Pericycle cells showed a unique cold response. Here the MTs were conspicuously cold-labile and quickly depolymerized near the root-tip. However, after 1 d many pericycle cells in more proximal regions had repolymerized their MTs as dense, randomly organized arrays. These persisted for the remainder of the cold treatment. A similar resistance to longterm chilling, by means of MT repolymerization, was found in cells of the root cap, quiescent centre and cells of the distal part of the former meristem. MT repolymerization in the cold may enable the apex to resume growth when more favourable (warmer) conditions return.
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  • 8
    ISSN: 1615-6102
    Keywords: Cytoskeleton ; Gravity perception ; Phleum ; Lepidium ; Lycopersicum ; Root cap ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Indirect immunofluorescence, using monoclonal antibodies to actin and tubulin, applied to sections of root tips ofLepidium, Lycopersicon, Phleum, andZea, revealed features of the cytoskeleton that were unique to the statocytes of their root caps. Although the cortical microtubules (CMTs) lay in dense arrays against the periphery of the statocytes, these same cells showed depleted complements of endoplasmic microtubules (EMTs) and of actin microfilament (AMF) bundles, both of which are characteristic of the cytoskeleton of other post-mitotic cells in the proximal portion of the root apex. The scarcity of the usual cytoskeletal components within the statocytes is considered responsible for the exclusion of the larger organelles (e.g., nucleus, plastids, ER elements) from the interior of the cell and for the absence of cytoplasmic streaming. Furthermore, the depletion of dense EMT networks and AMF bundles in statocyte cytoplasm is suggested as being closely related to the elevated cytoplasmic calcium content of these cells which, in turn, may also favour the formation of the large sedimentable amyloplasts by not permitting plastid divisions. These latter organelles are proposed to act as statoliths due to their dynamic interactions with very fine and highly unstable AMFs which enmesh the statoliths and merge into peripheral AMFs-CMTs-ER-plasma membrane complexes. Rather indirect evidence for these interactions was provided by showing enhanced rates of statolith sedimentation after chemically-induced disintegration of CMTs. All these unique properties of the root cap statocytes are supposed to effectively enhance the gravity-perceptive function of these highly specialized cells.
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Planta 181 (1990), S. 269-274 
    ISSN: 1432-2048
    Keywords: Cell development, growth ; Form factor (cell shape) ; Root (cell growth) ; Zea (root, cell growth)
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The onset of rapid cell elongation occurred at different distances from the apex in various tissues of the primary root of maize (Zea mays L.). Furthermore, the comparison of these distances with those determined for the cessation of mitotic divisions revealed a considerable discrepancy. The onset of rapid cell elongation was realized much farther from the root apex than the cessation of cell divisions and therefore a distinct region could be distinguished in every examined maize root tissue. This region was denoted the region of postmitotic ‘isodiametric’ cell growth. Cells in this region grew in width as well as in length and obtained approximately a square-isodiametric shape. They were also characterized, as are cells in the meristem, by intense nucleic-acid metabolism. This prominent postmitotic ‘isodiametric’ cell growth was observed in both polyploid and diploid tissues, and indicates that postmitotic ‘isodiametric’ cell growth, like mitotic division and cell elongation growth, represents an important developmental stage in plant cell ontogeny.
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  • 10
    ISSN: 1432-2048
    Keywords: Cell (growth polarity, shape) ; Gibberellin ; Growth polarity (root cortex) ; Microtubule ; Zea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The role of gibberellins and cortical microtubules in determining the polarity of cell growth in the root cortex of maize (Zea mays L.) was examined. Inhibition of gibberellin biosynthesis, either naturally through mutation (d5 mutant) or by means of chemicals such as 2S,3S paclobutrazol, caused thickening of root apices and increased their starch content. Immunofluorescence microscopy of cortical microtubules, coupled with a comparison of cell widhts, lengths and shapes, indicated that the meristem and immediate post-mitotic zone were the targets of gibberellin deficiency. Cortical cells in these regions were impaired in their ability to develop highly ordered transversal arrays of cortical microtubules. Consequently, the cells became wider and shorter. Application of gibberellic acid re-established the arrangements of cortical microtubules and the polarity of cell growth characteristic for roots having normal levels of gibberellins, it also decreased the starch content. These results indicate that gibberellins are morphogenetically active substances, not only in shoots but also in roots of maize.
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