Biomedical subjects

A M Emons

Publications and source records attributed to A M Emons.

11 recordsLinked to original sources

PubMed2001

A dynamical model for plant cell wall architecture formation.

We discuss a dynamical mathematical model to explain cell wall architecture in plant cells. The highly regular textures observed in cell walls reflect the spatial organisation of the cellulose microfibrils (CMFs), the most important structural component of cell walls. Based on a geometrical theory proposed earlier [A. M. C. Emons, Plant, Cell and Environment 17, 3-14 (1994)], the present model describes the space-time evolution of the density of the so-called rosettes, the CMF synthesizing complexes. The motion of these rosettes in the plasma membrane is assumed to be governed by an optimal packing constraint on the CMFs plus adherent matrix material, that couples the direction of motion, and hence the orientation of the CMF being deposited, to the local density of rosettes. The rosettes are created inside the cell in the endoplasmatic reticulum and reach the cell-membrane via vesicles derived from Golgi-bodies. After being inserted into the plasma membrane they are assumed to be operative for a fixed, finite lifetime. The plasma membrane domains within which rosettes are activated are themselves also supposed to be mobile. We propose a feedback mechanism that precludes the density of rosettes to rise beyond a maximum dictated by the geometry of the cell. The above ingredients lead to a quasi-linear first order PDE for the rosette-density. Using the method of characteristics this equation can be cast into a set of first order ODEs, one of which is retarded. We discuss the analytic solutions of the model that give rise to helicoidal, crossed polylamellate, helical, axial and random textures, since all cell walls are composed of (or combinations of) these textures.

Cell Wall↗

PubMed2000

Spectrin-like proteins in plant nuclei.

We analysed the presence and localization of spectrin-like proteins in nuclei of various plant tissues, using several anti-erythrocyte spectrin antibodies on isolated pea nuclei and nuclei in cells. Western blots of extracted purified pea nuclei show a cross-reactive pair of bands at 220-240 kDa, typical for human erythrocyte spectrin, and a prominent 60 kDa band. Immunolocalization by means of confocal laser scanning microscopy reveals spectrin-like proteins in distinct spots equally distributed in the nucleoplasm and over the nuclear periphery, independent of the origin of the anti-spectrin antibodies used. In some nuclei tracks of spectrin-like proteins are also observed. No signal is present in nucleoli. The amount and intensity of signal increases when nuclei were extracted, successively, with detergents, DNase I and RNase A, and high salt, indicating that the spectrin-like protein is associated with the nuclear matrix. The labelling is similar in nuclei of various plant tissues. These data are the first that show the presence and localization of spectrin-like epitopes in plant nuclei, where they may stabilize specific interchromatin domains.

Cell Fractionation↗

PubMed2000

How the deposition of cellulose microfibrils builds cell wall architecture.

Cell walls, the extracytoplasmic matrices of plant cells, consist of an ordered array of cellulose microfibrils embedded in a matrix of polysaccharides and glycoproteins. This construction is reminiscent of steel rods in reinforced concrete. How a cell organizes these ordered textures around itself, creating its own desirable environment, is a fascinating question. We believe that nature adopted an economical solution to this design problem: it exploits the geometrical constraints imposed by the shape of the cell and the limited space in which microfibrils are deposited, enabling the wall textures essentially to 'build themselves'. This does not imply that the cell cannot control its wall texture. On the contrary, the cell has ample regulatory mechanisms to control wall texture formation by controlling the insertion of synthases and the distance between individual microfibrils within a wall lamella.

Cell Membrane↗

PubMed2000

The cytoskeleton in plant and fungal cell tip growth.

Tip-growing cells have a particular lifestyle that is characterized by the following features: (1) the cells grow in one direction, forming a cylindrical tube; (2) tip-growing cells are able to penetrate their growth environment, thus having to withstand considerable external forces; (3) the growth velocity of tip-growing cells is among the fastest in biological systems. Tip-growing cells therefore appear to be a system well suited to investigating growth processes. The cytoskeleton plays an important role in cell growth in general, which is why tip-growing cells provide an excellent model system for studying this aspect. The cytoskeletal system comprises structural elements, such as actin filaments and microtubules, as well as proteins that link these elements, control their configuration or are responsible for transport processes using the structural elements as tracks. Common aspects as well as differences in configuration and function of the cytoskeleton in various types of tip-growing cells reveal the general principles that govern the relationship between the cytoskeleton and cell growth.

Cytoskeleton↗

PubMed2000

Lipochito-oligosaccharide nodulation factors stimulate cytoplasmic polarity with longitudinal endoplasmic reticulum and vesicles at the tip in vetch root hairs.

Vetch root hair development has four stages: bulge, growing, growth terminating, and full-grown hair. In the assay we used, the nodulation factor induced swellings and outgrowths in growth-terminating hairs. Bulges, swellings, and full-grown hairs have transverse endoplasmic reticulum (ER) and no tip-accumulated vesicles. Growing hairs and outgrowths show vesicle accumulation in the tip and longitudinal subapical ER. Bulge walls and walls of swellings appear mottled.

Antigens, Bacterial↗

PubMed2000

Alterations in the actin cytoskeleton of pollen tubes are induced by the self-incompatibility reaction in Papaver rhoeas.

Self-incompatibility (SI) is a genetically controlled process used to prevent self-pollination. In Papaver rhoeas, the induction of SI is triggered by a Ca(2)+-dependent signaling pathway that results in the rapid and S allele-specific inhibition of pollen tube tip growth. Tip growth of cells is dependent on a functioning actin cytoskeleton. We have investigated the effect of self-incompatibility (S) proteins on the actin cytoskeleton in poppy pollen tubes. Here, we report that the actin cytoskeleton of incompatible pollen tubes is rapidly and dramatically rearranged during the SI response, not only in our in vitro SI system but also in vivo. We demonstrate that nonspecific inhibition of growth does not result in similar actin rearrangements. Because the SI-induced alterations are not observed if growth stops, this clearly demonstrates that these alterations are triggered by the SI signaling cascade rather than merely resulting from the consequent inhibition of growth. We establish a detailed time course of events and discuss the mechanisms that might be involved. Our data strongly implicate a role for the actin cytoskeleton as a target for signaling pathways involved in the SI response of P. rhoeas.

Actins↗

PubMed1999

Spectrin-like proteins in green algae (Desmidiaceae).

Immunochemical detection of actin as well as spectrin-like proteins have been carried out in the green algae Micrasterias denticulata, Closterium lunula, and Euastrum oblongum. In these algae, actin is detected on Western blots at 43 kDa with antibodies to actin from higher plant and animal origin. By use of antibodies to human and chicken erythrocyte spectrin a cross-reactivity with desmid proteins is found at about the molecular mass of 220 kDa, where also human erythrocyte spectrin is detected. Additional bands are present at 120 kDa and 70 kDa, which are probably breakdown products. An antibody against chicken alpha-actinin, a small protein of the spectrin superfamily, recognizes bands at 90 kDa, where it is expected, and 70 kDa, probably the same breakdown product as mentioned for spectrin. Isoelectric focusing provides staining at pI 4.6 with antibodies against spectrin. Immunogold labelling of spectrin and alpha-actinin antigens on high-pressure frozen, freeze-substituted Micrasterias denticulata cells with the same antibodies exhibits staining, especially at membranes of different populations of secretory vesicles, at dictyosomes, and the plasma membrane. However, no clear correlation to the growth pattern of the cell could be observed. Taken together, our results demonstrate the presence of spectrin-like proteins in desmid cells which are probably functional in exocytosis.

Actinin↗

PubMed1998

The making of the architecture of the plant cell wall: how cells exploit geometry.

Cell wall deposition is a key process in the formation, growth, and differentiation of plant cells. The most important structural components of the wall are long cellulose microfibrils, which are synthesized by synthases embedded in the plasma membrane. A fundamental question is how the microfibrils become oriented during deposition at the plasma membrane. The current textbook explanation for the orientation mechanism is a guidance system mediated by cortical microtubules. However, too many contraindications are known in secondary cell walls for this to be a universal mechanism, particularly in the case of helicoidal arrangements, which occur in many situations. An additional construction mechanism involves liquid crystalline self-assembly [A. C. Neville (1993) Biology of Fibrous Composites: Development Beyond the Cell Membrane (Cambridge Univ. Press, Cambridge, U.K.)], but the required amount of bulk material that is able to equilibrate thermally is not normally present at any stage of the wall deposition process. Therefore, we have asked whether the complex ordered texture of helicoidal cell walls can be formed in the absence of direct cellular guidance mechanisms. We propose that they can be formed by a mechanism that is based on geometrical considerations. It explains the genesis of the complicated helicoidal texture and shows that the cell has intrinsic, versatile tools for creating a variety of textures. A compelling feature of the model is that local rules generate global order, a typical phenomenon of life.

Journal Article↗

PubMed1998

The ipiO gene of Phytophthora infestans is highly expressed in invading hyphae during infection.

The expression of the in planta-induced gene ipiO of the potato late blight pathogen Phytophthora infestans was analyzed during various developmental stages of its life cycle. ipiO mRNA was detected in zoospores, cysts, germinating cysts, and young mycelia, but not in sporangia or in old mycelia grown in vitro. ipiO is not only expressed in stages prior to infection but also during colonization of potato and tomato leaves. In disease lesions, ipiO mRNA was detected in the water-soaked area and the healthy-looking plant tissue surrounding it. In contrast, ipiO mRNA was not found in necrotized tissue or in sporulating areas of a lesion. To determine more precisely the location and time of ipiO gene expression in planta, cytological assays were performed using a P. infestans transformant expressing a transcriptional fusion between the ipiO1 promoter and the beta-glucuronidase (GUS) reporter gene. GUS staining was found specifically in the subapical and vacuolated area of tips of invading hyphae. The histochemical GUS assays demonstrate that ipiO is expressed during biotrophic stages of the disease cycle.

Blotting, Northern↗

PubMed1997

Ethylene provides positional information on cortical cell division but is not involved in Nod factor-induced root hair tip growth in Rhizobium-legume interaction.

Nod factors secreted by Rhizobium leguminosarum bv. viciae induce root hair deformation, involving a reinitiation of tip growth, and the formation of nodule primordia in Vicia sativa (vetch). Ethylene is a potent inhibitor of cortical cell division, an effect that can be counteracted by applying silver ions (Ag+) or aminoethoxy-vinylglycine (AVG). In contrast to the inhibitory effect on cortical cell division, ethylene promotes the formation of root hairs (which involves tip growth) in the root epidermis of Arabidopsis. We investigate the possible paradox concerning the action of ethylene, putatively promoting Nod factor induced tip growth whilst, at the same time, inhibiting cortical cell division. We show, by using the ethylene inhibitors AVG and Ag+, that ethylene has no role in the reinitiation of root hair tip growth induced by Nod factors (root hair deformation) in vetch. However, root hair formation is controlled, at least in part, by ethylene. Furthermore, we show that ACC oxidase, which catalizes the last step in ethylene biosynthesis, is expressed in the cell layers opposite the phloem in that part of the root where nodule primordia are induced upon inoculation with Rhizobium. Therefore, we test whether endogenously produced ethylene provides positional information controlling the site where nodule primordia are formed by determining the position of nodules formed on pea roots grown in the presence of AVG or Ag+.

Amino Acid Oxidoreductases↗

PubMed1985

Microtubules in root hairs.

The microtubules of root hairs of Raphanus sativus, Lepidium sativum, Equisetum hyemale, Limnobium stoloniferum, Ceratopteris thalictroides, Allium sativum and Urtica dioica were investigated using immunofluorescence and electron microscopy. Arrays of cortical microtubules were observed in all hairs. The microtubules in the hairs show net axial orientations, but in Allium and Urtica helical microtubule patterns are also present. Numerical parameters of microtubules in Raphanus, Equisetum and Limnobium were determined from dry-cleave preparations. The results are discussed with respect to cell wall deposition and cell morphogenesis.

Allium↗