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At least 73 records · Page 4Linked to original sources
PubMed2005

Anisotropic expansion of the plant cell wall.

Plants shape their organs with a precision demanded by optimal function; organ shaping requires control over cell wall expansion anisotropy. Focusing on multicellular organs, I survey the occurrence of expansion anisotropy and discuss its causes and proposed controls. Expansion anisotropy of a unit area of cell wall is characterized by the direction and degree of anisotropy. The direction of maximal expansion rate is usually regulated by the direction of net alignment among cellulose microfibrils, which overcomes the prevailing stress anisotropy. In some stems, the directionality of expansion of epidermal cells is controlled by that of the inner tissue. The degree of anisotropy can vary widely as a function of position and of treatment. The degree of anisotropy is probably controlled by factors in addition to the direction of microfibril alignment. I hypothesize that rates of expansion in maximal and minimal directions are regulated by distinct molecular mechanisms that regulate interactions between matrix and microfibrils.

Anisotropy↗
PubMedDate not supplied

Signal transduction in plant cells.

In plants, unlike animals, signal transduction studies are in their infancy. While intracellular Ca2+ appears to have second messenger functions, attempts to show that protein kinases, inositol phosphates and cyclic AMP are involved in signal transduction in plants have run into considerable difficulty.

Calcium↗
PubMed2000

Loosening of plant cell walls by expansins.

Plant cell walls are the starting materials for many commercial products, from lumber, paper and textiles to thickeners, films and explosives. The cell wall is secreted by each cell in the plant body, forming a thin fibreglass-like network with remarkable strength and flexibility. During growth, plant cells secrete a protein called expansin, which unlocks the network of wall polysaccharides, permitting turgor-driven cell enlargement. Germinating grass pollen also secretes an unusual expansin that loosens maternal cell walls to aid penetration of the stigma by the pollen tube. Expansin's action has puzzling implications for plant cell-wall structure. The recent explosion of gene sequences and expression data has given new hints of additional biological functions for expansins.

Allergens↗
PubMed1983

Rumen microbial attachment and degradation of plant cell walls.

The plant cell wall of forages is a complex entity of cellulose fibers found in a matrix of hemicellulose and pectins. Different microbial types including bacteria, protozoa, and fungi associate with plant cell walls during incubation with rumen fluid. Bacteria, the major degraders of the forage cell wall, often firmly attach to the forage cell wall before digestion. Encapsulated cocci and irregularly shaped or pleomorphic bacteria are the predominant types of bacteria that adhere to and degrade cell walls. Although certain bacterial types adhere to particular forages, no consistent association was found between digestibility and the type of adhering bacteria. Bacteria adhere to the more rigid forage cell walls and adhere, or are close to, the more easily degraded cell walls. Tissues delignified with potassium permanganate or treated with sodium hydroxide (to improve forage digestibility) show a loss of electron denseness. These tissues separate into individual cells, which at times appear as microfibrils in the cell walls. Research is needed on forages of higher fiber content to mitigate the barriers that limit the attack on forage cell walls by rumen microorganisms.

Animals↗
PubMed2003

Actin-based photo-orientation movement of chloroplasts in plant cells.

In photosynthesizing plant cells, chloroplasts change their arrangements and/or positions in response to light irradiation. These photo-orientation movements of chloroplasts are believed to play important roles in optimizing the photosynthetic activity of plant cells. We have been investigating the roles of the actin cytoskeleton in the intracellular movement and positioning of chloroplasts using the aquatic monocot Vallisneria gigantea Graebner and the terrestrial dicot Spinacia oleracea L. (spinach). In Vallisneria epidermal cells, chloroplasts accumulate on the cytoplasmic layer facing the top surface (outer periclinal layer) under dim red light, whereas they move to the cytoplasmic layer perpendicular to the outer periclinal layer (anticlinal layer) under strong blue light. Concomitant with these responses, actin filaments exhibit dramatic changes in their configurations. The possible modes of action of the actin cytoskeleton to regulate the movement and positioning of chloroplasts are briefly summarized, together with our recent analysis of the association of actin filaments with chloroplasts isolated from spinach leaves.

Actins↗
PubMed1985

Actin organization during the cell cycle in meristematic plant cells. Actin is present in the cytokinetic phragmoplast.

The distribution and organisation of F-actin during the cell cycle of meristematic root-tip cells of Allium was investigated using a rhodamine-labelled phalloidin to stain F-actin in isolated cell preparations. Such preparations could, in addition, be stained for tubulin by immunofluorescence, enabling a comparison between F-actin and microtubule distributions in the same cell. In interphase, an extensive array of actin-filament bundles was present in the cytoplasm of elongating cells, the bundles generally following the long axis of the cell and passing in close proximity to the nucleus. In contrast, the interphase microtubule array occupied the cortex of the cell and was oriented at right angles to the actin bundles. In smaller, isodiametric cells, microfilament arrays were present but less well developed. During cell division, phalloidin-specific staining was seen in the cytokinetic phragmoplast, and co-distributed with microtubules at all stages of cell plate formation; however, neither the pre-prophase band nor the mitotic spindle were stained with phalloidin. Co-distribution of F-actin and microtubules only occurs, therefore, at cytokinesis. The relationship between microfilaments and microtubules is discussed, together with the possible role of actin in the phragmoplast.

Actins↗
PubMed2000

[The establishment of two new evaluation criteria for cell state of plant cell suspension cultures].

An experiment on suspending rice cell cultures in sucrose solution and on optical density (OD) value in culture solution at 576 nm wave width was carried out, the result indicates that suspension rate (%) of suspensions, while suspending in 0.76 mol/L sucrose solution for 15 minutes at room temperature, can be employed as an judgment criterion of cell state. Suspending cell suspension in 0.76 mol/L sucrose solution is also a good approach on selecting cells from suspension cell mass, as a result, it is beneficial to establishing cell suspension. The browning of cell suspension is related to the necrosis degree of suspension cells. OD value of cell suspension liquid at 576 nm can be taken as a criterion with which the necrosis degree of cell suspension can be evaluated.

Cell Culture Techniques↗
PubMed2003

Meiotic transmission of epigenetic changes in the cell-division factor requirement of plant cells.

During the development of tobacco plants, cells undergo epigenetic changes that alter their requirement in culture for the cell-division factor cytokinin. Cultured leaf cells alternate between cytokinin-requiring (C-) and cytokinin-independent (C+) states at extremely high rates of approximately 10-2 per cell generation by a process called pseudodirected variation. Here we show that plants regenerated from most C+ clones express the Habituated leaf (Hl) trait, i.e., leaf tissues exhibit the C+ phenotype rather than the wild-type C- phenotype in culture. This new trait then segregates as a monogenic dominant trait indicating that conversion of C- cells to C+ cells is associated with a meiotically transmissible, genetic modification. Two independent mutants, Hl-2 and Hl-3, derived from C+ variants arising in culture were unstable in planta and reverted gametically at rates roughly comparable to pseudodirected variation in culture. Cells of the Hl-2 mutant, but not of a stable Hl-1 mutant, reverted phenotypically at high rates in culture. This revertant C- phenotype persisted in some plants regenerated from cloned revertant lines, and then showed irregular segregation in two successive sexual generations. These results show for the first time that meiotically transmissible epimutations can occur reversibly and at high rates in culture.

Cell Division↗
PubMed2005

Epothilone D affects cell cycle and microtubular pattern in plant cells.

Epothilones, macrocyclic lactones from culture filtrates of the myxobacterium Sorangium cellulosum, are known as taxol-like microtubular drugs in human medicine. To date, nothing is known about the effect of epothilones on microtubules (MTs) in plant cells and/or on the plant cell cycle. As shown in this report, the treatment of tomato cell suspension cultures with epothilone D produced a continuous increase in the mitotic index. Dose-response curves revealed that epothilone D alters the mitotic index at concentrations as low as 1.5 microM. Mitotic arrest was already visible after only 2 h of treatment, and 55% of the cells were arrested after 24 h. As shown by immunocytological methods, abnormal spindles are formed during metaphase, which leads to a random distribution of chromosomes in the whole cell and prevents the formation of a metaphase plate. The process of chromosome decondensation does not seem to be affected, because micronuclei form at the same place with the distributed chromosomes. This suggests that epothilone D influences the stability of plant MTs mainly during metaphase of the mitotic cycle. In metaphase, the effects of epothilone D seem to be irreversible, because cells with an abnormal spindle could not be recovered after removal of the drug.

Cell Cycle↗
PubMed2003

The architecture of polarized cell growth: the unique status of elongating plant cells.

Polarity is an inherent feature of almost all prokaryotic and eukaryotic cells. In most eukaryotic cells, growth polarity is due to the assembly of actin-based growing domains at particular locations on the cell periphery. A contrasting scenario is that growth polarity results from the establishment of non-growing domains, which are actively maintained at opposite end-poles of the cell. This latter mode of growth is common in rod-shaped bacteria and, surprisingly, also in the majority of plant cells, which elongate along the apical-basal axes of plant organs. The available data indicate that the non-growing end-pole domains of plant cells are sites of intense endocytosis and recycling. These actin-enriched end-poles serve also as signaling platforms, allowing bidirectional exchange of diverse signals along the supracellular domains of longitudinal cell files. It is proposed that these actively remodeled end-poles of elongating plant cells remotely resemble neuronal synapses.

Actins↗
PubMed1998

Use of plant cell cultures in biotechnology.

Plant cell cultures are being widely used in scientific studies on the physiology, biochemistry and molecular biology of primary and secondary metabolism, developmental regulation and cellular responses to pathogens and stress. In this chapter the significance of plant cell cultures in biotechnology is discussed with special emphasis on commercial production of secondary metabolites and pharmaceuticals, the potential of genetically transformed cell cultures, photosynthetically active cell cultures, production of somatic embryos, and novel assay systems based on the use of plant cells. Future aspects of biotechnical applications with respect to the potentials and limitations of these approaches are assessed, particularly in comparison with the productivity of lower eucaryotes.

Biotechnology↗
PubMed1990

Activation of promutagens by plant cell systems.

The plant cell/microbe coincubation assay is a sensitive and flexible assay for use in screening for plant-mediated promutagens as well as in basic mutation research. By using plant cell cultures of crop plants, xenobiotics used in agriculture can be evaluated for their mutagenic properties.

Biotransformation↗
PubMed1996

Agrobacterium VirE2 protein mediates nuclear uptake of single-stranded DNA in plant cells.

Agrobacterium genetically transforms plant cells by transferring a single-stranded DNA (ssDNA) copy of the transferred DNA (T-DNA) element, the T-strand, in a complex with Agrobacterium proteins VirD2, bound to the 5' end, and VirE2. VirE2 binds single-stranded nucleic acid cooperatively, fully coating the T-strand, and the protein localizes to the plant cell nucleus when transiently expressed. The coupling of ssDNA binding and nuclear localizing activities suggests that VirE2 alone could mediate nuclear localization of ssDNA. In this study, fluorescently labeled ssDNA accumulated in the plant cell nucleus specifically when microinjected as a complex with VirE2. Microinjected ssDNA alone remained cytoplasmic. Import of VirE2-ssDNA complex into the nucleus via a protein import pathway was supported by (i) the inhibition of VirE2-ssDNA complex import in the presence of wheat germ agglutinin or a nonhydrolyzable GTP analog, both known inhibitors of protein nuclear import, and (ii) the retardation of import when complexes were prepared from a VirE2 mutant impaired in ssDNA binding and nuclear import.

Bacterial Proteins↗
PubMed2006

An anisotropic-viscoplastic model of plant cell morphogenesis by tip growth.

Plant cell morphogenesis depends critically on two processes: the deposition of new wall material at the cell surface and the mechanical deformation of this material by the stresses resulting from the cell's turgor pressure. We developed a model of plant cell morphogenesis that is a first attempt at integrating these two processes. The model is based on the theories of thin shells and anisotropic viscoplasticity. It includes three sets of equations that give the connection between wall stresses, wall strains and cell geometry. We present an algorithm to solve these equations numerically. Application of this simulation approach to the morphogenesis of tip-growing cells illustrates how the viscoplastic properties of the cell wall affect the shape of the cell at steady state. The same simulation approach was also used to reproduce morphogenetic transients such as the initiation of tip growth and other non-steady changes in cell shape. Finally, we show that the mechanical anisotropy built into the model is required to account for observed patterns of wall expansion in plant cells.

Anisotropy↗