Plant Cell Wall Growth Research Articles

Cu/Zn superoxide dismutases in developing cotton fibers: evidence for an extracellular form

Hydrogen peroxide and other reactive oxygen species are important signaling molecules in diverse physiological processes. Previously, we discovered superoxide dismutase (SOD) activity in extracellular protein preparations from fiber-bearing cotton (Gossypium hirsutum L.) seeds. We show here, based on immunoreactivity, that the enzyme is a Cu/Zn-SOD (CSD). Immunogold localization shows that CSD localizes to secondary cell walls of developing cotton fibers. Five cotton CSD cDNAs were cloned from cotton fiber and classified into three subfamilies (Group 1: GhCSD1; Group 2: GhCSD2a and GhCSD2b; Group 3: GhCSD3 and GhCSD3s). Members of Group 1 and 2 are expressed throughout fiber development, but predominant during the elongation stage. Group 3 CSDs are also expressed throughout fiber development, but transiently increase in abundance at the transition period between cell elongation and secondary cell wall synthesis. Each of the three GhCSDs also has distinct patterns of expression in tissues other than fiber. Overexpression of cotton CSDs fused to green fluorescent protein in transgenic Arabidopsis demonstrated that GhCSD1 localizes to the cytosol, GhCSD2a localizes to plastids, and GhCSD3 is translocated to the cell wall. Subcellular fractionation of proteins from transgenic Arabidopsis seedlings confirmed that only c-myc epitope-tagged GhCSD3 co-purifies with cell wall proteins. Extracellular CSDs have been suggested to be involved in lignin formation in secondary cell walls of other plants. Since cotton fibers are not lignified, we suggest that extracellular CSDs may be involved in other plant cell wall growth and development processes.

Ectopic expression of Expansin3 or Expansinβ1 causes enhanced hormone and salt stress sensitivity in Arabidopsis

Expansins are cell wall loosening proteins that appear to permit the microfibril matrix network to slide in growing plant cell walls, thereby enabling the wall to expand. To scrutinize possible impacts on plant growth and development when expansins are over-expressed, we characterized phenotypic alterations of the transgenic plants that constitutively expressed AtEXP3 or AtEXP-beta1 under control of 35S-CaMV promoter. Our results suggest that both AtEXP3-OX and AtXPbeta1-OX are very sensitive to salt stress. However, the mechanisms underlying their enhanced salt sensitivity appear to be different.

The plant cell wall. * Rose JKC, ed 2003. * Oxford: CRC Press. 99.50 (hardback). * 381 pp.

Cell walls have long been recognized as important and unique features of plant cells, contributing not only to the architecture of plant organs but also to the control of growth, to the exclusion of pathogens and to the production and transmission of signalling molecules. Gross measurements of plant cell composition established long ago that the plant devotes a large proportion of its biosynthetic endeavours to building walls. In addition, however, the sequencing of the Arabidopsis genome has recently highlighted the cell wall as something to which the plant devotes an unexpectedly large proportion of its genes – some 15% of them. Why, for example, should Arabidopsis have eighty-odd genes apparently encoding pectin methylesterases? Why are there thirty-odd xyloglucan endotransglucosylase/endohydrolases (XTHs) and α-expansins? These are among the questions to which our current knowledge of plant cell wall biology cannot provide the answers. Research into this branch of science is clearly set to continue for some years to come. There are no modern texts focusing, at the research level, on aspects of the biology and chemistry of plant cell walls. Brett and Waldron's Physiology and Biochemistry of Plant Cell Walls (Chapman & Hall, 1996) is a valuable introduction, particularly for teaching purposes. My own book, The Growing Plant Cell Wall: Chemical and Metabolic Analysis (The Blackburn Press, 2000), deals specifically with methodology. Linskens and Jackson's Plant Cell Wall Analysis (Springer, 1996) concentrates on certain relatively narrow topics such as olive pulp cell walls. Joss Rose has therefore identified an important gap in the literature. It would be inaccurate to say that the book ‘fills’ this gap – rather it occupies some of the space within it. Many topics remain to be dealt with more fully by future authors. Nevertheless, the present book is an extremely valuable addition to the literature. The ten chapters are all by different authors (27 authors in total), and thus the style and approach vary throughout the book, inevitably favouring the authors' own interests. Nevertheless, I found all ten chapters valuable and up-to-date reviews of the selected topics. The topics covered range from the chemical (structure and composition of polysaccharides and lignin) and biophysical (infra-red spectroscopy, atomic force microscopy, polymer interactions and the mechanism of cell expansion) to the cytological, metabolic and developmental. The final chapter (partly written by the editor) specifically deals with ‘plant cell walls in the post-genomic era’, a topic that overlaps usefully with the previous nine chapters and allows a helpful summing-up. Many of the earlier chapters already focus heavily on the exploitation of information gained from genomic analysis; and, probably because of space limitations, this has led to a degree of sketchiness in the coverage of some fundamentals, e.g. of chemistry, metabolism and cytology. For example, shaded ovals, hexagons and rectangles do not adequately substitute for chemical formulae for imparting information on the structures of GPI anchors (Fig. 4.3); and O is used as a one-letter abbreviation for an amino acid, presumably hydroxyproline, without definition. On the other hand there are some interesting novel ideas, which deserve a higher profile, for example the idea that supercoiling of tethering xyloglucan chains contributes to the tension between neighbouring microfibrils (Fig. 1.11). The book will be most suitable for research students, postdocs and academics. Advanced undergraduates undertaking project work in this field will also find it useful as a guide to the original literature. All photographs are monochrome, which, although fine for electron micrographs, is perhaps a little restrictive for modern light (including fluorescence) microscopy. However, this is a well-referenced, well-indexed and well-produced book, which deserves to be very widely used.

Synthetic genes for the elucidation of glycosylation codes for arabinogalactan-proteins and other hydroxyproline-rich glycoproteins.

Hydroxyproline-rich glycoproteins (HRGPs) are ubiquitous architectural components of the growing plant cell wall, accounting for as much as 10-20% of the dry weight. HRGPs are implicated in all aspects of plant growth and development, including responses to stress. The HRGP superfamily contains three major groups which represent a continuum of peptide periodicity and hydroxyproline-O-glycosylation. These groups range from the highly periodic and lightly arabinosylated repetitive proline-rich proteins (PRPs), through the cross-linked extensins which are periodic and highly arabinosylated, to the arabinogalactan-proteins (AGPs) which are the most highly glycosylated and least periodic. The repetitive units are small, often only four- to six-residue-glycosylated modules viewed hypothetically as functional motifs, or glycomodules. The Hyp contiguity hypothesis predicts that Hyp arabinosylation increases with Hyp contiguity and that clustered noncontiguous Hyp residues are sites of arabinogalactan polysaccharide addition in the AGPs and gums. Recent results involving glycosylation site mapping of endogenous HRGPs and HRGP design using synthetic genes have corroborated the hypothesis. The uses of synthetic genes in HRGP glycosylation site mapping and structural/functional analysis are also discussed.

Structure and functions of feruloylated polysaccharides

Cell wall polysaccharides contain a small amount of ester-linked hydroxycinnamic acid derivatives, such as p-coumaric and ferulic acids. These hydroxycinnamic acids can be coupled oxidatively to form the acid dimers. Dimer formation in the growing plant cell wall would cause the cross-linkage of cell wall polysaccharides and lead to an increase in wall rigidity. Feruloyl polysaccharide esters would also participate with lignin monomers in oxidative coupling pathways to generate a ferulate-polysaccharide-lignin complexes during cell wall development. Feruloyl oligosaccharides derived from feruloyl polysaccharides have been shown to inhibit cell elongation growth induced by auxin or gibberellins. Feruloyl polysaccharides are critical entities in directing wall cross-linking and in limiting biodegradability by microorganisms.

Role of transglycosylation in the integration of xyloglucan into the growing plant cell wall in vivo

Abstract Xyloglucan endotransglycosylase (XET) activity is widespread in plant cell walls, but its action on xyloglucan in vivo has been difficult to prove because the reaction products are not expected to differ chemically from the reactants. By feeding of cultured Rosa cells with [13C]glucose and [3H]arabinose followed by [12-C]glucose, and isopyenic centrifugation of the extracted xyloglucan in caesium trifluoroacetate, we have obtained evidence for the annealing of segments of newly-secreted xyloglucan to xyloglucan chains that were already present in the cell wall. This is the first evidence for interpolymeric transglycosylation of xyloglucan in vivo.

Lipo-oligosaccharide nodulation factors: A new class of signaling molecules mediating recognition and morphogenesis

Jean Dbnari6 and Julie Cullimore Laboratoire de Biologie Moleculaire des Relations Plantes-Microorganismes CNRS-INRA, 31326 Castanet-Tolosan Cedex France The legume-rhizobia symbiosis is estimated to fix per an- num as much nitrogen as the fertilizer industry and is of great agronomic and ecological importance. This efficient nitrogen-fixing association occurs as a result of the forma- tion of a new specialized organ, the root nodule, which is induced by the prokaryotic symbiont on its specific plant partner (see Nap and Bisseling, 1990). The rhizobial genes that determine the host recognition and nodulation have recently been found to specify the synthesis of excreted lipo-oligosaccharide signals (Figure 1) which are capable of eliciting, at extremely low concentrations, many of the plant responses characteristic of the bacteria themselves. These responses include the initiation of cell division, in- duction of specific changes in cell morphology, and trig- gering of a plant organogenic program leading to the for- mation of the nodule. This review focuses on the role of this new class of signaling molecules in host-partner rec- ognition and nodule development in the legume-rhizobia symbiosis. Rhizobia, Prokaryotes that Elicit a Specific Plant Organogenesis Rhizobia (now classified into three genera, Rhizobium, Sradyrhizobium and Azorhizobium) are soil bacteria that can elicit the formation of nitrogen-fixing nodules on the roots of selected species of the legume family. Some of these bacteria exhibit a narrow host range of nodulation; for example three of the species discussed in this review, R. meliloti, R. leguminosarum biovar viciae and B. japoni- cum nodulate respectively alfalfa, pea/vetch and soybean and not each other’s hosts. In contrast R. sp. NGR234 has a broad host range, nodulating over 70 legume genera and even a non-legume, Parasponia (see Denarie et al., ‘I 992). Symbiotic nodule formation is based on two processes, plant infection and induction of a novel organ (Nap and Bisseling, 1990). To penetrate into their hosts, rhizobia elicit stimulation and reorientations of plant cell wall growth, presumably due to a restructuring of the cytoskele- ton. These changes result in both the entrapment of the bacteria within root hair curls and also the initiation and development of infection threads, tubular structures ,through which bacteria pass on their way down the root hair to the underlying cortical cell layers (Figure 2A). Ahead of the advancing threads a major developmental switch is elicited in the root cortex. Cortical cells are induced to dedifferentiate and divide, and a meristem is then formed, whose functioning generates the nodule. Nodules have a particular ontogeny and anatomy; they are not mere tu- mors but fully differentiated organs divided into a number of cell-types and tissues. Alfalfa nodules for example (Fig- ure 28) contain a distal meristem, an infection zone, a zone where the cells are filled with nitrogen-fixing bacteria, and vascular bundles that ensure metabolic exchanges with the rest of plant. Genetic manipulation of the prokaryotic partner has led to the identification of a set of rhizobial genes (the nod genes) required for infection, nodulation and the control of host specificity (Figure 1). The expression these genes isdependent upon plant signals, usuallyflavonoids, excreted in root exudates. In the presence of appropriate plant inducers, rhizobial NodD regulatory proteins activate the transcription of thestructural nodgenes. Among these, and present in all rhizobia, are common nodA% genes, in which mutations lead to a complete abolition of infection and nodulation. In addition, there are nod genes that are species/strain specific, such as noV De- narie et al., 1992; Fisher and Long, 1992). Nodulation Genes Specify the Production of Lipo-Oligosaccharide Nod Factors What could be the biochemical function of the rhizobial nod gene products? A link between the genetic determi-

A proton nuclear magnetic resonance study of the physical changes in growing plant cell walls

Changes in broadline proton nuclear magnetic resonance parameters of cell walls during growth of etiolated hypocotyls of bean (Phaseolus vulgaris L.) indicate that cell wall structure becomes more rigid during development. Most of the changes are completed in the first 6 cm below cotyledon insertion and are correlated with increased restriction of proton movements in regions of dense polymer packing.

Cell adhesion, cell separation and plant morphogenesis

A simplified and useful view of plant cell development is that it involves the spatial and temporal organization of cell division, cell expansion and cell differentiation all taking place within the constraints of a lack of cell migration. A facet of such development that has often been neglected, is understanding how the cells of a developing structure hold fast or adhere. Subsequently in development the adhered cells of apices or embryos give rise to more loosely attached cells in mature structures where the degree of cell separation and intercellular space formation is developmentally regulated. Recent cell biological studies, most significantly in the derivation of monoclonal antibody probes forthe plant cell surface (Knox, 1992; Roberts, 1990), have increased our awareness of the local modifications of cell walls and rekindled interest in aspects of plant cell wall adhesion and intercellular space formation. It seems timely to examine our current understanding of the mechanisms of cell adhesion and separation and their importance for plant morphogenesis. Molecular probes for cell surface components offer immense potential, not only for the specific study of the local wall modifications such as those resulting in cell separation but also as probes of molecular markers of cell identity relating to position and context. This essay attempts to draw some of the threads together regarding both the nature and importance of cell adhesion and cell separation in plant tissues.

Liquid crystal order and turbulence in the planar twist of the growing plant cell walls

During growth, the plant cell wall behaves as a dynamic structure that exemplifies a case of unstable balance between a capability to organize a characteristic order and a permanent tendency to destroy the order. This interpretation allows previous results to be complemented and reappraised; it also integrates the cell wall behavior into a unified frame. The wall thickenings are structured according to a crystal-like pattern (cholesteric mesophase). Laminar helicoids are locally deposited on cell facets and form actual flat and planar twists in which the causes of topological defects are minimized. The helicoidal pattern is short-lived and its occurrence results from a complex interplay between self-assembly and disassembly properties. Two alternative processes destroy this critical state: 1. Externally, the surface extension which produces a progressive degradation and a randomization by shearing and stretching; 2. Internally, aleatory and punctual instabilities which alter the genesis of the system at the plasmalemma/wall interface. As the time goes on, the twisting either resumes or, in contrast, the perturbation increases. The system tends to become unpredictable thus suggesting turbulence.

Book reviews

The Growing Plant Cell Wall, by S. C. Fry.The LK Pesticide Guide 1988, edited by G. W Ivens.Handbook of Plants with Pest‐control Properties, by M. Grainge and S. Ahmed.The Crop Protection Directory 1988–89, edited by Elaine Warrell.Leptographium Root Diseases of Conifers edited by T C. Harrington and F W Cobb. Jr.Laboratory Exercises in Plant Pathology: An Instructional Kit, edited for the American Phytopathological Society by A. B. A. M. Baudoin with the assistance of G. R. Hooper, D. E. Mathre and R. B. Carroll.Wheat and Wheat Improvement, second edition, edited for the American Society of Agronomy by E. G. Heyne.

Changements cytochimiques et ultrastructuraux des parois cellulaires de la pellicule du raisin, Vitis vinifera, durant la croissance et la maturation de la baie

Cytochemical and ultrastructural analysis of cell wall characteristics was performed in the dermal system of the grape berry (Vitis vinifera L. cv. Pinot noir), using a test for polysaccharides (periodic acid – thiosemicarbazide – silver proteinate, associated with dimethylsulfoxide extraction). Samples were examined at successive stages of fruit development. The main events of the first growth phase, i.e., thickening of hypodermal cell walls and their tangential extension, continued during the second growth phase. At all the stages of grape development, tangentially expanding walls were typical of actively growing plant cell walls, with an ordered texture, new layer deposition, and progressive rotation of microfibrillar subunits (bow-shaped patterns). At maturity, hydration, swelling of the walls, and an increase in the amount of soluble pectic substances were noticed. No redifferentiation of the cell walls occurred. The cuticle, already differentiated into two layers at the first growth phase, was clearly lamellar during the second. At maturity a number of layers, distinguishable by their cytochemical reactivity, were detected. Cuticle thickness increased during "véraison" and was maintained throughout the second growth phase. A considerable increase in the content of epicuticular waxes was noticed during ripening.

Structure and function of plant cell wall polysaccharides.

Studies of the primary structures of polysaccharides of growing plant cell walls have shown that these structures are far more complex than was anticipated just a few years ago. This complexity can best be appreciated by considering xyloglucan, a hemicellulose present in the cell wall of both monocots and dicots, and rhamnogalacturonan II (RG-II) and rhamnogalacturonan I (RG-I), two structurally unrelated pectic polysaccharides. This realization led us to postulate that cell wall polysaccharides have functions beyond determining the size, shape and strength of plants. Some years ago we demonstrated that oligosaccharide fragments of a branched beta-linked glucan of fungal cell walls can elicit the production of phytoalexins (antibiotics) in plants by inducing the formation of the enzymes responsible for synthesis of the phytoalexins. It has now been ascertained and confirmed by synthesis that the elicitor activity resides in a very specific hepta-beta-D-glucoside. The heptaglucoside has been shown to elicit phytoalexins by activating the expression of specific genes, that is, by causing the synthesis of the mRNAs that encode the enzymes that synthesize phytoalexins. In other words, complex carbohydrates can be regulatory molecules. Further experiments established that oligosaccharide fragments of polysaccharides, produced by acid or base hydrolysis or by enzymolysis of primary cell walls of plants, also evoked defence responses in plants. Subsequently, we learned that defined fragments of polysaccharides, released from covalent attachment within plant cell walls, can function as regulators of various physiological processes such as morphogenesis, rate of cell growth and time of flowering and rooting, in addition to activating mechanisms for resisting potential pathogens. Examples of plant oligosaccharides with regulatory properties (called oligosaccharins) will be described.

Calcium movements and the cellular basis of gravitropism

An early gravity-transduction event in oat coleoptiles which precedes any noticeable bending is the accumulation of calcium on their prospective slower-growing side. Sub-cellular calcium localization studies indicate that the gravity-stimulated redistribution of calcium results in an increased concentration of calcium in the walls of responding cells. Since calcium can inhibit the extension growth of plant cell walls, this selective accumulation of calcium in walls may play a role in inducing the asymmetry of growth which characterizes gravitropism. The active transport of calcium from cells into walls is performed by a calcium-dependent ATPase localized in the plasma membrane. Evidence is presented in support of the hypothesis that this calcium pump is regulated by a feed-back mechanism which includes the participation of calmodulin.

In vitro and in vivo polysaccharides assembly: ultrastructural and cytochemical study of growing plant cell wall components.

Wall morphogenesis in higher plants is a problem still open to controversy. Until now the possibility of a transmembrane control and the involvement of microtubules were mostly envisaged. Self-assembly processes have been observed in the case of walls of Chlamydomonas and bacteria. Spontaneous gelling interactions between xanthan and galactomannan from Ceratonia have been analyzed very recently. The present work provides indications that some processes of spontaneous aggregation could occur in higher plants during the formation and expansion of cell wall.Observations were performed on hypocotyl of mung bean (Phaseolus aureus) for which growth characteristics and wall composition have been previously defined.In situ, the walls of actively growing cells (primary walls) show an ordered three-dimensional organization (fig. 1). The wall is typically polylamellate with multifibrillar layers alternately transverse and longitudinal. Between these layers intermediate strata exist in which the orientation of microfibrils progressively rotates. Thus a progressive change in the morphogenetic activity occurs.

The Growth of Plant Cell walls

Publisher Summary 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.

Structure and Growth of Plant Cell-Walls

The Plant Cell-Wall By Prof. Pieter A. Roelofsen. (Encyclopedia of Plant Anatomy, Band 3, Teil 4.) Pp. vii + 335 + 68 plates. (Berlin-Nikolassee: Gebruder Borntraeger, 1959.) n.p.