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Studies on the Growth Hormone of Plants: V. The Relation of Cell Elongation to Cell Wall Formation.

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... However, it was the American plant biochemist James F. Bonner (1910Bonner ( -1996 who discovered, in a landmark-paper of 1934, the "acid-growtheffect". With reference to earlier studies, Bonner (1934) 22 documented that, when coleoptile segments are incubated in acid solutions (pH ca. 4.0), they rapidly elongate over a period of 1 to 2 h, as if they would have been incubated in IAA. ...
... Nearly five decades ago, Cleland (1970) 23 and Hager et al. (1971) 24 independently proposed that auxin rapidly causes the initiation of cell elongation in excised segments via the secretion of protons, leading to the acidification of "the cell wall". Unfortunately, these pioneers of modern IAA-research did not refer to the work of Sachs (1870, 1887), 2,5 Bonner (1934), 22 and many others, who had clearly shown that, in coleoptiles and stems, the sturdy outer wall(s) are the growth-limiting structure(s). Accordingly, over subsequent decades, the role of the epidermal cell layer was largely ignored, until a major "Zea mays study" was published. ...
... The question as to how IAA achieves its control over the "irreversible stretching-ability" of the OEW is one of the greatest enigmas in plant biology since the 1930s. [10][11][12][22][23][24] As mentioned above, IAAinduced wall acidification appears to be insufficient to promote cell elongation. As an alternative, a "cytological model" has been proposed and recently described in detail. ...
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The year 2020 marks the 150th anniversary of the elucidation of the process of plant organ growth at the cellular level by Julius Sachs (1870). In this Addendum to a Review Article in Molecular Plant, we describe this fundamental discovery and argue that the etiolated grass coleoptile still represents the system of choice for the experimental analysis of auxin (indole-3-acetic acid, IAA)-action. With reference to the phenomenon of ‘tissue tension’, we discuss the acid-growth hypotheses of IAA-induced wall loosening and the process of vacuolar expansion, respectively. IAA-mediated elongation appears to be independent of wall acidification, and may be regulated via the secretion of glycoproteins into the outer epidermal wall, whereby turgor (and tissue) pressure provides the ‘driving force’ for growth. As predicted by the “acid growth-hypothesis”, the fungal phytotoxin Fusicoccin (Fc) induces organ elongation via the rapid secretion of protons. We conclude that “cell elongation” can only be understood at the level of the entire organ that displays biomechanical features not established by single cells. This systems-level approach can be traced back to the work of Sachs (1870).
... With such a mode of cell expansion, one expects a perfect correlation between wall incorporation and cell elongation. Subsequent studies on excised oat coleoptile segments (Heyn and Van Overbeek 1931) and on Avena coleoptiles (Bonner 1934) showed that the addition of "growth substance" (later christened auxin) could in certain conditions stimulate cell elongation without a change in the wall synthesis rate. Heyn and Van Overbeek (1931) showed instead that auxin stimulated the plastic extensibility of oat coleoptile walls. ...
Chapter
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The cell wall (CW) is astrong but dynamic exoskeleton, which determines the wide variety of cell shapes (for review see Martin etal. 2001) and provides amechanical barrier against pathogens (Vorwerk etal. 2004). CW structure and composition vary according to cell type and growth stage: the primary CW is athin and constantly modified structure allowing cell growth driven by turgor pressure (see Verbelen and Vissenberg, in this volume), whereas secondary CWs are thick and rigid structures, which are laid down as soon as the cell has reached its final size. Cellulose microfibrils (CMFs) constitute the fibre component of the composite material that makes up the plant CW. Cellulose represents 10–14% of the dry weight of primary CWs, 40–60% of secondary CWs and up to 98% in specialized cells, such as cotton fibres. CMFs are highly oriented and in this way influence the mechanical properties and viscoplasticity of the wall (see Burgert and Fratzl, in this volume). Recent data suggest that, besides controlling cell shape, cellulose synthesis also plays acritical role in the transition between cellular growth stages. In this chapter we focus on the question of how the synthesis and deposition of cell wall material is coordinated with cell expansion in different cell types. Although several actors involved in cellulose synthesis have been identified, the mechanism and regulation of deposition remain largely unknown. Also, how cellulose associates with other CW polymers and how the cells monitor the status of the cell wall is not understood. We will first describe how genetic screens allowed the isolation of key components of the cellulose synthesis machinery in primary and secondary CWs. Next we will discuss recent findings on the role of CW synthesis in the control of cell expansion.
... Low w w induced by osmoticum typically allows wall synthesis to continue (Bonner 1934;Loescher and Nevins 1972;Iraki et al. 1989a;Wakabayashi et al. 1997;Sakurai et al. 1987;Zhong and Lauchli 1993). In soils having low w w , Sweet et al. (1990) found continued wall synthesis but at a lower rate than at high w w , consistent with our results. ...
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In dark-grown soybean (Glycine max [L.] Merr.) seedlings, exposing the roots to water-deficient vermiculite (psi(w)=-0.36 MPa) inhibited hypocotyl (stem) elongation. The inhibition was associated with decreased extensibility of the cell walls in the elongation zone. A detailed spatial analysis showed xyloglucan endotransglucosylase (XET; EC 2.4.1.207) activity on the basis of unit cell wall dry weight was decreased in the elongation region after seedlings were transplanted to low psi(w). The decrease in XET activity was at least partially due to an accumulation of cell wall mass. Since cell number was only slightly altered, wall mass had increased per cell and probably led to increased wall thickness and decreased cell wall extensibility. Alternatively, an increase in cell wall mass may represent a mechanism for regulating enzyme activity in cell walls, XET in this case, and therefore cell wall extensibility. Hypocotyl elongation was partially recovered after seedlings were grown in low-psi(w) vermiculate for about 80 h. The partial recovery of hypocotyl elongation was associated with a partial recovery of cell wall extensibility and an enhancement of XET activity in the hypocotyl elongation zone. Our results indicate XTH proteins may play an important role in regulating cell wall extensibility and thus cell elongation in soybean hypocotyls. Our results also showed an imperfect correlation of spatial elongation and XET activity along the hypocotyls. Other potential functions of XTH and their regulation in soybean hypocotyl growth are discussed.
... The wall grows in part by being stretched by P because interpolymeric bonds in the matrix naturally break and re-form, and when under tension from P the polymers tend to slip past each other irreversibly, enlarging the wall (Cleland, 1971;Taiz, 1984). Typically, the stretching enlarges the cell 10-to 100-fold (Roberts, 1994) but under normal conditions the walls do not become proportionately thinner (Bonner, 1934;Loescher and Nevins, 1973;Bret-Harte et al., 1991). The wall increases in mass and volume while continuing to support the protoplast and resist the strain produced by P. As much as 90-99 % of the wall is new by the time the cell matures (Roberts, 1994). ...
Article
Plant growth involves pressure-driven cell enlargement generally accompanied by deposition of new cell wall. New polysaccharides are secreted by the plasma membrane but their subsequent entry into the wall is obscure. Therefore, polysaccharides and gold colloids of various sizes were presented to the inner wall face as though they were secreted by the plasma membrane. Primary cell walls were isolated from growing internodes of Chara corallina and one end was attached to a glass capillary. Solutions of dextran or suspensions of gold colloids were pushed into the lumen by oil in the capillary. The oil did not enter the wall, and the solution or suspension was pressed against the inner wall face, pressurized at various 'artificial' P (turgor pressure), and polymer or colloid movement through the wall was monitored. Interstices in the wall matrix had a diameter of about 4.6 nm measured at high P with gold colloids. Small solute (0.8 nm) readily moved through these interstices unaffected by P. Dextrans of 3.5 nm diameter moved faster at higher P while dextran of 9 nm scarcely entered unless high P was present. Dextran of 11 nm did not enter unless P was above a threshold, and dextran of 27 nm did not enter at P as high as 0.5 MPa. The walls filtered the dextrans, which became concentrated against the inner wall face, and most polymer movement occurred after P stabilized and bulk flow ended. P created a steep gradient in concentration and mechanical force at the inner wall face that moved large polymers into small wall openings apparently by starting a polymer end or deforming the polymer mechanically at the inner wall face. This movement occurred at P generally accepted to extend the walls for growth.
... Across higher plants and algae, there may be different mechanisms of surface expansion, including localized wall loosening by expansins (e.g. Cosgrove, 1996; Fleming et al., 1997) or localized delivery of wall material (intussusception; see Bonner, 1934). However, the overall constraints on growth rates and patterning boundaries to generate coherent form are greatly shared in all organisms, unicellular or multicellular , in which the parts of the growing surface do not change their relative positions after formation, i.e. in which there is no phenomenon such as cell migration as seen in animals. ...
Article
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A study is made by computation of the interplay between the pattern formation of growth catalysts on a plant surface and the expansion of the surface to generate organismal shape. Consideration is made of the localization of morphogenetically active regions, and the occurrence within them of symmetry-breaking processes such as branching from an initially dome-shaped tip or meristem. Representation of a changing and growing three-dimensional shape is necessary, as two-dimensional work cannot distinguish, for example, formation of an annulus from dichotomous branching. For the formation of patterns of chemical concentrations, the Brusselator reaction-diffusion model is used, applied on a hemispherical shell and generating patterns that initiate as surface spherical harmonics. The initial shape is hemispherical, represented as a mesh of triangles. These are combined into finite elements, each made up of all the triangles surrounding each node. Chemical pattern is converted into shape change by moving nodes outwards according to the concentration of growth catalyst at each, to relieve misfits caused by area increase of the finite element. New triangles are added to restore the refinement of the mesh in rapidly growing regions. The postulated mechanism successfully generates: tip growth (or stalk extension by an apical meristem) to ten times original hemisphere height; tip flattening and resumption of apical advance; and dichotomous branching and higher-order branching to make whorled structures. Control of the branching plane in successive dichotomous branchings is tackled with partial success and clarification of the issues. The representation of a growing plant surface in computations by an expanding mesh that has no artefacts constraining changes of shape and symmetry has been achieved. It is shown that one type of pattern-forming mechanism, Turing-type reaction-diffusion, acting within a surface to pattern a growth catalyst, can generate some of the most important types of morphogenesis in plant development.
Chapter
It appears from the preceding chapters of this volume that growth under almost all circumstances is more or less intimately connected with metabolism. One experimental difficulty in studies of growth is to discern conditions directly, or more or less directly, affecting growth from those connected with metabolism not specifically essential for growth. This also holds true with regard to chemical growth factors. — Let us consider a unicellular bacterium or an alga. Its growth depends upon the external supply of different organic and inorganic compounds. According to the prevailing conditions sometimes one, sometimes another is deficient, thus becoming the chemical factor limiting growth. Together they form a heterogeneous set of chemical growth factors with varying modes of action.
Article
It was investigated the influence of CCC (2-chloroethyl-trimethylammonium-chloride), hexamethonium, decamethonium and AMO-1618 on cell wall polysaccharide synthesis of wheat coleoptile segments. Under the influence of growth retardants there is no variation in the relation between ¹⁴C-incorporation rates of the different cell wall fractions (during a 5 hours incubation period). In every case the cell elongation is more inhibited by the growth retardants than the synthesis of cell wall polysaccharides. It is supposed that treated coleoptiles contain more cell wall material per cell wall surface unit than the control.
Article
According to the acid-growth hypothesis, auxin-induced secretion of hydrogen ions activate "wall loosening" enzymes that change the rheological properties of the cell wall. The wall loosening process may yield monosaccharides by the enzymic cleavage of load-bearing polysaccharides. Our study was initiated to determine the metabolic fate of such sugars when released from the major hemicellulosic polysaccharides of the cell walls of Zea mays coleoptiles.Excised coleoptile sections accumulated radioactive glucose, arabinose, and xylose supplied in an incubation medium, and the radioactivity from these sugars was incorporated into polysaccharides. At least 50% of the radioactivity from glucose accumulated in the soluble neutral sugar fraction regardless of external concentrations. The distribution of radioactivity from xylose into all subcellular fractions was similar to that from glucose, indicating that xylose was converted to glucose before being used by the coleoptile. IAA increased the incorporation of glucose into cell wall polysaccharide and neutral sugar pools when the exogenous concentration was higher than 1 millimolar.Over 80% of the radioactivity from arabinose accumulated by the coleoptile sections was incorporated into soluble and noncellulosic polymers; IAA induced an increase in the incorporation of arabinose into noncellulosic polymers by 22%. Accumulation of radioactivity from arabinose into polysaccharide was enhanced by IAA at concentrations of exogenous arabinose up to 33 millimolar.IAA promoted the incorporation of both arabinose and glucose into cell wall polysaccharides even when elongation was inhibited by CaCl(2), indicating that the influence of IAA was not a consequence of the growth response.
Article
Promotion of cell wall synthesis (from glucose) in pea (Pisum sativum) stem segments by indoleacetic acid (IAA) develops over a period of 1 to 2 hours and is comprised of a promotion of glucose uptake plus a promotion of the utilization of absorbed glucose. The effect of IAA resembles, in these and other respects, its effect on cell wall synthesis in oat coleoptile segments, but the pea system differs in not being inhibited by galactose or mannose, in involving considerably more isotope dilution by endogenous substrates, and in certain other respects.EFFECTOR INFLUENCES UPON AND TOTAL ACTIVITIES OF THE FOLLOWING ENZYMES OBTAINED FROM ETIOLATED PEA STEM SEGMENTS PRETREATED WITH OR WITHOUT IAA WERE EXAMINED: phosphoglucomutase, uridine diphosphate glucose (UDP-glucose) pyrophosphorylase, nucleoside diphosphokinase, UDP-glucose dehydrogenase, inorganic pyrophosphatase, hexokinase (particulate and soluble), and UDP-glucose-beta-1,4-glucan-glucosyl transferase (beta-glucan synthetase). The first three enzymes mentioned exhibit high activity relative to the flux in vivo, do not appear to show physiologically significant effector responses, and are concluded not to be control points. UDP-glucose dehydrogenase activity is regulated by UDP-xylose. Hexokinase is a potential control point but does not exhibit regulatory effects related to the IAA response. beta-Glucan synthetase is the only one of these enzymes with activity which is increased by treatment of tissue with IAA, and this may be responsible for the effect of IAA on wall synthesis.Assays of metabolite pools support the conclusion that stimulation of polysaccharide synthesis by IAA is due partly to changes in hexokinase reaction rate resulting from an increase in metabolic glucose pool size caused by increased glucose uptake, and partly to increased activity at the polysaccharide synthetase level.
Article
In order to assess the role of the mechanical properties of the wall in auxin-induced cell elongation, a study has been made of the ability of isolated Avena coleoptile walls to extend (creep) when subjected to a constant applied stress. Creep occurs as a viscoelastic extension which has the following characteristics: the extension is proportional to log time and is partly reversible, and the extension rate has a Q(10) of about 1.05 and is markedly greater in auxin-pretreated walls. In nonconditioned walls the extension rate is proportional to applied stress, but pre-extension causes the appearance of an apparent yield strain. The similarity of creep and instantaneous plastic deformation in response to temperature or to pretreatment with auxin or KCN suggests that the instantaneous deformation is simply the viscoelastic extension which occurs at very short times. A comparison of these viscoelastic properties with the properties of auxin-induced cell elongation indicates that cell elongation requires more than just a physical extension of the wall. It is suggested that elongation occurs as a series of extension steps, each of which involves a viscoelastic extension preceded or accompanied by an auxin-dependent biochemical change in the wall properties.
Article
It is established that auxin, indoleacetic acid, increases the rate of cell elongation in Avena coleoptile by causing the cell walls to become more easily stretched, more plastic. This was first demonstrated by Heyn (16), who showed that coleoptiles treated with auxin were more readily stretched by an applied weight than coleoptiles not so treated. Heyn's observation has been confirmed and extended by Tagawa and Bonner (33).
Article
Ray, Peter M. (U. Michigan, Ann Arbor.) Cell wall synthesis and cell elongation in oat coleoptile tissue. Amer. Jour. Bot. 49(9): 928–939. Illus. 1962.—Cell wall synthesis in oat coleoptile cylinders tends to run parallel with but not usually proportional to cell elongation both under promotion by auxin and sugar and under inhibition by supraoptimal auxin or sugar, or by a variety of other inhibitors. Inhibitors of elongation fall into 2 classes with respect to their effects on wall synthesis: (1) those which inhibit the 2 processes approximately equally (galactose, mannose, mannitol, azide, iodoacetate, dinitrophenol, low temperature, supraoptimal auxin) and (2) those which inhibit elongation percentagewise much more strongly than wall synthesis, so that as complete inhibition of elongation is approached, substantial wall synthesis continues (Ca+ +, fluoride, arsenite, mercurials). When coleoptile cylinders elongate in the absence of sugar, the cell walls appear to become markedly thinner, and in some experiments negligible increase in total wall material apparently occurs. However, the amount of α-cellulose does rise. Increase in cell wall material occurs during elongation of cylinders at 2 C. The results are interpreted as indicating that during elongation the bulk of new cell wall material is added by apposition, but a certain proportion of the new material is probably introduced within the existing wall structure and induces its expansion.
Article
This chapter describes the cell walls of higher plants, algae, and fungi. Cell wall development of higher plants can be divided into two parts: one of which is concerned with an account of mitosis and cytokinesis and the establishment of the position and plane of the dividing cell wall between the two daughter nuclei, and the other which will indicate the subsequent enlargement and growth of the wall first in area (the primary cell wall), and then in thickness (the secondary cell wall). The general nutritional supply of materials such as amino acids, sugars, lipids, minerals, and vitamins or particular growth factors such as auxins, kinins, and gibberellins can influence both aspects of growth and cell wall development. The general organization of the algae walls appears to be similar to that of higher plants and consists of an organized microfibrillar system, embedded in a matrix. In the red and brown algae the microfibrils are not normally orientated with respect to the cell wall and thus the whole structure is isotropic; however in some algae the microfibrils are arranged in definite directions either in the complete wall or in layers of the wall. A large number of fungal cell walls are made up of a complex system of microfibrils, embedded in a matrix. Chitin is the characteristic polysaccharide of many fungal cell walls and it seems to be present as the principal constituent of the microfibrils.
Article
This chapter discusses the growth of plant cell walls. In the course of cell growth, that may involves an increase in cell surface by a factor somewhere between 10 and 105, the wall grows accordingly, retaining in this process a remarkable unity, constancy, and coherence of structure. Growth involves increase in thickness as well as in area; these may increase simultaneously or successively. The tough elastic membrane characteristic of the mature cell is thus commonly its most conspicuous part, and in the aggregate such membranes form the skeletal framework of the plant. The fundamental feature of wall structure is its dual nature. Electron microscopy reveals the presence of microfibrils of indefinite length. Morphological studies of wall structure and growth refer almost wholly to the micellar or microfibrillar component of the wall which has these supramolecular features of structure. The chapter discusses the microfibrillar framework and its changes in growth, and also the nonfibrillar matrix of the wall and its role in wall extensibility.
Article
1. A new method is described which gives a continuous record of the absolute rate of protoplasmic streaming in epidermal cells of the Avena coleoptile. 2. With this method a study was made of the influence of malate and iodoacetate on streaming velocity, in order to make correlations with the previously established effects of these substances on growth and respiration. 3. In the presence of optimum concentrations of indole-3-acetic acid in freshly cut sections, malate had no effect on streaming. In the presence of very low concentrations of the auxin, however, malate increased the range of response, so that the threshold of auxin sensitivity was lowered some ten times by the malate. Malate alone had no effect on streaming. 4. In coleoptile sections, soaked overnight in sugar solution or in water, the acceleration of streaming normally caused by auxin almost disappears, but the presence of malate causes large accelerations of streaming by the auxin. 5. Similarly, in sections from old coleoptiles, which no longer show acceleration of streaming by auxin, the acceleration is restored when malate is added together with the auxin. 6. Malate does not enter the cell as rapidly as does auxin, but easily detectable amounts penetrate within 30 minutes. 7. Iodoacetate in the concentration which inhibits growth (5 x 10(-5)M) completely inhibits the acceleration of streaming by auxin. In still lower concentrations iodoacetate slightly accelerates streaming. Higher concentrations, up to 2 x 10(-4)M, did not reduce the rate of streaming below that of controls without auxin. The effect of iodoacetate is therefore to inhibit the acceleration caused by auxin and not to affect the basal streaming rate. 8. It is concluded that, just as for growth and respiration, malate is necessary for the response to auxin shown by acceleration of streaming. This further strengthens the triple parallel between the effects of auxin on streaming, growth, and respiration, all of which are apparently mediated by the 4-carbon acid system.
Article
With their continuous growth, understanding how plant shapes form is fundamentally linked to understanding how growth rates are controlled across different regions of the plant. Much of a plant's architecture is generated in shoots and roots, where fast growth in tips contrasts with slow growth in supporting stalks. Shapes can be determined by where the boundaries between fast- and slow-growing regions are positioned, determining whether tips elongate, branch, or cease to grow. Across plants, there is a diversity in the cell wall chemistry through which growth operates. However, prototypical morphologies, such as tip growth and branching, suggest there are common dynamic constraints in localizing chemical growth catalysts. We have used Turing-type reaction-diffusion mechanisms to model this spatial localization and the resulting growth trajectories, characterizing the chemistry-growth feedback necessary for maintaining tip growth and for inducing branching. The mechanism defining the boundaries between fast- and slow-growing regions not only affects tip shape, it must be able to form new boundaries when the pattern-forming dynamics break symmetry, for instance in the branching of a tip. In previous work, we used an arbitrary concentration threshold to switch between two dynamic regimes of the growth catalyst in order to define growth boundaries. Here, we present a chemical dynamic basis for this threshold, in which feedback between two pattern-forming mechanisms controls the extent of the regions in which fast growth occurs. This provides a general self-contained mechanism for growth control in plant morphogenesis (not relying on external cues) which can account for both simple tip extension and symmetry-breaking branching phenomena.
Article
Background and Aims A study is made by computation of the interplay between the pattern formation of growth catalysts on a plant surface and the expansion of the surface to generate organismal shape. Consideration is made of the localization of morphogenetically active regions, and the occurrence within them of symmetry-breaking processes such as branching from an initially dome-shaped tip or meristem. Representation of a changing and growing three-dimensional shape is necessary, as two-dimensional work cannot distinguish, for example, formation of an annulus from dichotomous branching.Methods For the formation of patterns of chemical concentrations, the Brusselator reaction-diffusion model is used, applied on a hemispherical shell and generating patterns that initiate as surface spherical harmonics. The initial shape is hemispherical, represented as a mesh of triangles. These are combined into finite elements, each made up of all the triangles surrounding each node. Chemical pattern is converted into shape change by moving nodes outwards according to the concentration of growth catalyst at each, to relieve misfits caused by area increase of the finite element. New triangles are added to restore the refinement of the mesh in rapidly growing regions.Key Results The postulated mechanism successfully generates: tip growth (or stalk extension by an apical meristem) to ten times original hemisphere height; tip flattening and resumption of apical advance; and dichotomous branching and higher-order branching to make whorled structures. Control of the branching plane in successive dichotomous branchings is tackled with partial success and clarification of the issues.Conclusions The representation of a growing plant surface in computations by an expanding mesh that has no artefacts constraining changes of shape and symmetry has been achieved. It is shown that one type of pattern-forming mechanism, Turing-type reaction-diffusion, acting within a surface to pattern a growth catalyst, can generate some of the most important types of morphogenesis in plant development.
Chapter
Auch der Zustand der nichtwachsenden, aber lebenden und aktiven Zelle ist, wie wir wissen, dynamisch charakterisiert, als Gleichgewichtszustand, in dem der dauernd ablaufende Stoffabbau durch eine Synthese gleichen Umfanges bilanzmäßig kompensiert ist (Rittenberg und Mitarbeiter 1939, Vickery und Mitarbeiter 1939, Hevesy und Mitarbeiter 1940, Schoenheimer 1942, MacVicar und Burris 1948, Mazia und Prescott 1955 u. a.). Überwiegen die Synthesen die abbauenden Vorgänge, so arbeitet die Zelle mit Stoffgewinn, sie wächst. Diese Art des Wachstums, die wir, soweit wir nur die Zunahme der plasmatischen Zellbestandteile ins Auge fassesn, als Plasmawachstum bezeichnen, ist die fundamentale, die gewöhnlich auch den anderen Wachstumsformen, dem Teilungswachstum und dem Streckungswachstum, vorauszugehen hat, diese auch zum Teil noch begleitet.
Article
Sporophyte setae of Lophocolea heterophylla (a leafy liverwort) elongate solely as a result of the expansion of individual seta cells. Though seta walls thin considerably during elongation, colorimetric analysis indicates that 25-fold increase in seta cell length is accompanied by a 2-fold increase in cell wall carbohydrates. Carbohydrate reserves of setae were characterized histochemically and by paper chromatography. Starch diminishes during elongtion; polyfructosans and sucrose are replaced by fructose and glucose. Increase in wall material appears to be at the expense of these carbohydrate reserves in seta cells, and may be due as well to a transport of wall precursors from the gametophyte.
Article
Cell wall synthesis was studied by determining the incorporation of [14C]-glucose into epidermal and cortical cell walls of etiolated Pisum sativum L. cv. Alaska stem segments. Walls were fractionated into the matrix and cellulose components, and incorporation into these components assessed in terms of the total uptake of label into that tissue. When segments were allowed to elongate, the stimulation of total glucose uptake by indole-3-acetic acid (IAA) and fusicoccin (FC) was greater than their stimulation of incorporation. IAA and FC thus did not stimulate precursor incorporation in elongating segments. When elongation was inhibited by calcium, however, IAA and FC significantly promoted wall synthesis in the cortex and vasular tissue (which shows almost no growth or acidification response to auxin). In these tissues incorporation into matrix and cellulose was promoted approximately equally. In the epidermis (thought to be the tissue responsive to auxin in the control of growth), FC promoted a significant increase in wall synthesis, although less than that in the cortex, while there was some evidence of a similar promotion by IAA. Both IAA and FC had a greater effect on incorporation into the matrix component of the wall than into cellulose. The results that FC caused a substantial promotion of cell wall synthesis which was not due solely to elongation, and that the inner non-growth responsive cortical tissues can respond to IAA. Moreover, a comparison of the effects of IAA and FC on the different components of the wall suggests that the response in the epidermis differs from that in the other tissues.
Article
The dependence of auxin-induced growth on continued cell wall synthesis was investigated in stem segments of etiolated pea (Pisum sativum L. cv. Alaska) seedlings using the cell wall synthesis inhibitors monensin and 2,6-dichlorobenzonitrile (DCB). Monensin (5 μM) potently inhibited indole-3-acetic acid (IAA)-induced growth, particularly during the second hour of treatment, whereas growth in fusicoccin (FC) was inhibited much less effectively. Incorporation of [14C]-glucose into both matrix and cellulose fractions of the wall showed a sharp increase beginning after about 60 min, this rise being promoted by both IAA and FC. Monensin inhibited this rise in incorporation of label and completely removed the promotion of this by IAA, although some promotion by FC remained. Monensin inhibited incorporation into cellulose in a manner similar to that into matrix, but the use of the apparently specific cellulose synthesis inhibitor DCB showed that cellulose synthesis could be strongly inhibited without effect on growth, at least in the short term. The results support the view that sustained auxin-induced growth depends upon the incorporation of new matrix cell wall components into the wall.
Article
The effects of IAA and galactose on the endogenous levels of UDP-sugars and nu-cleotides were compared between a monocotyledon, using coleoptile segments of oat (Avena sativa L. cv. Victory I) and a dicotyledon, using epicotyl segments of azuki bean (Vigna angularis Owhi and Ohashi cv. Takara). The following results were obtained: From these results, we conclude that UTP is involved in the IAA action and also in the differential effects of galactose on the UDP-glucose formation, which is needed for cell wall synthesis and ensuing cell elongation.
Article
Solute generation and cell wall synthesis were examined in sunflower hypocotyl peripheral layers, the growth rate of which had been altered by gravistimulation. Measurements of both the concentrations of the major solutes and the osmotic potential showed that although upper cells stopped growing, the solute levels in these cells continued to increase at rates comparable to those in lower cells. This indicated that altered growth rates, generated during gravicurvature, are not based on solute generation but must result from cell wall changes. Gravimetric and precursor incorporation studies showed that net wall synthesis continued in upper cells despite their lack of growth. An ultrastructural study of the epidermal cells on the uppermost (non-elongating) and lowermost (elongating) surfaces of horizontal cucumber hypocotyls showed that the relative amounts of the various membrane fractions were similar in upper and lower cells despite their very different growth rates.
Article
The activities of the enzymes of uridine diphosphate sugar interconversions (UDP-D-glucose 4-epimerase, UDP-D-glucuronate 4-epimerase, UDP-D-xylose 4-epimerase, UDP-D-glucose dehydrogenase and UDP-D-glucuronate decarboxylase) were measured by using enzymic preparations (protein precipitated between 40-65% (NH4)2SO4 saturation) isolated from segments at different stages of elongation of the third internode of pea seedlings. All enzymic activities increased from dividing and non-elongated cells to fully elongated cells. At all stages of growth, the specific activity or the activity per cell of UDP-D-glucose dehydrogenase was much lower than that of UDP-D-glucuronate decarboxylase and this may represent a controlling step in the formation of UDP-D-xylose. During elongation, changes were also found in the activities of the epimerases. These could be correlated with the corresponding variations which occur in the chemical structure and physical properties of pectins during cell wall extension. However, the high levels of the epimerases present in cells which have completed elongation growth suggest that pectin synthesis is mainly controlled at the sites of the synthetase reactions.
Article
Avena coleoptile sections were treated with a fraction of a fungal filtrate containing a potent cellulase. Elongation rate was not affected although turgor pressure remained constant and wall extensibility was increased. These data show that the simple weakening of cell walls is not sufficient to promote growth and suggest that endogenous polysaccharidases are not the means by which the growth rate of the coleoptile is regulated.
Chapter
This chapter provides an overview of plant cell-walls. The cell wall is an envelope that encases the plant cell. The wall must be rigid enough to give the plant strength and form, and yet, if necessary, it must yield freely to facilitate growth. The network of cell walls, where adjoining cells have a wall in common, provides in a plant the structural framework analogous to both the skin and the bones of an animal. In some plants, especially those having woody tissues, the strength of this cell-wall network is prodigious. However, despite their apparently tough sheathing, the cells of the growing regions of a plant are able to extend to many times their initial length. The cell wall lies outside the plasma membrane, which defines the boundaries of the cell itself. The wall is freely permeable to most molecules, but the membrane exhibits selective permeability tending to concentrate certain dissolved molecules and ions inside the cell. The presence of such charged components as acidic polysaccharides within the wall imparts ion-exchange properties to the wall. The chapter discusses the concepts related to the types of cell-wall polysaccharides and elaborates the methods used in the elucidation of primary-wall structure. It also presents an overview of cell-wall glycoproteins.
Article
The effects of galactose on IAA‐induced elongation and endogenous level of UDP‐glucose (UDPG) in oat (Avena sativa L. cv. Victory) coleoptile segments were examined under various growth conditions to see if there was a correlation between the level of UDPG and auxin‐induced growth. The following results were obtained: Galactose (10 mM) inhibited the auxin‐induced cell elongation of oat coleoptile segments after a lag of ca 2 h. Determinations of cell wall polysaccharides and UDP‐sugars indicated that galactose, when inhibiting the cell wall polysaccharide synthesis, decreased the level of UDPG but caused an increase in the levels of Gal‐1‐P and UDP‐Gal. When coleoptile segments treated with IAA and galactose were transferred to galactose‐free IAA‐solution, the segment elongation was restored and the amounts of cell wall polysaccharides increased. During this period, the amount of UDPG increased and the levels of Gal‐1‐P and UDP‐Gal slightly decreased or leveled off. The UDP‐pentoses changed similarly as UDPG did. Addition of sucrose (30 mM) enhanced IAA‐induced cell elongation and removed growth inhibition by 1 mM galactose. Sucrose increased the amounts of the cell wall polysaccharides and the level of UDPG in the presence or absence of IAA and also counteracted the decrease in UDPG caused by galactose. These results indicate that the level of UDPG is an important limiting factor for cell wall biosynthesis and, thus, for auxin‐induced elongation.
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