Biogenesis, and Expansion. PLANT CELLS, UNLIKE ANIMAL CELLS, are surrounded by a rela- tively thin but mechanically strong cell wall. This wall consists of. PDF | On Jan 1, , Jean-Paul Joseleau and others published The Plant Cell Walls () medical-site.info PDF | Plant cell walls are among the features that distinguish plants from animals. The cell wall contributes to internal cellular turgor pressure while offering.
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synthesis is essential to the study of cell wall function in plant growth and development and for The plant cell wall is a complex macromolecular structure that. tion and diversity of chemical and structural features of the plant cell walls. National Laboratory, Oak Ridge, TN (medical-site.info ton. used in order to study the structure of the primary cell wall of that the sycamore cell wall contains a pectic rhamnogalactu- ronan polymer, and.
Bacterial peptidoglycan. Overview and evolving concepts H. Labischinski, H. Maidhof 3.
Biosynthesis of the bacterial peptidoglycan unit J. Utilization of lipid-linked precursor and formation of peptidoglycan in the process of cell growth and division M. Molecular biology of bacterial septation J. Ayala, T. Garrido, M. Biochemistry of the penicilloyl serine transferases J. Ghuysen and G. Microbial peptidoglycan murein hydrolases G. Shockman, J. Cell wall changes during bacterial endospore formation C. Buchanan, A. Henriques, P.
Teichoic acid synthesis in Bacillus Subtitis H. Pooley, D. Lipoteichoic acids and lipoglycans W. Cell-wall-associated proteins in Gram-positive bacteria M. TFA releases primarily non-cellulosic polysaccharides; however, also parts of cellulose from regions containing kinks or dislocations will be hydrolyzed.
The supernatant was filtered with 0. The separated monosaccharides were quantified using calibration with monosaccharide standards l-arabinose, l-rhamnose, d-xylose, d-galactose, d-glucose, d-glucuronic and d-galacturonic acid Sigma. The content of intact cellulose microfibrils in the TFA-resistant pellet was quantified based on the method reported by [ 37 ]. Cellulose content was determined in triplicate for each sample. Comprehensive microarray polymer profiling CoMPP The analysis was performed essentially according to the method reported by [ 38 , 39 ].
Each extraction was done in triplicates and pooled to one sample. The probes used in this study are specific for plant cell wall polymers and listed in Additional file 1 : Table S1. The signal strength was quantified using Array-Pro Analyzer 6. Methylesterification degree of uronic acids The degree of methylesterification was analysed by saponification of AIR followed by enzymatic oxidation of methanol released by alcohol oxidase, as described by [ 40 , 41 ] with modifications.
Afterwards, the solution was neutralized with HCl and centrifuged. Ground barley and oat flour, provided by the manufacturer, served as reference material. Mixed-linkage glucan content was determined in triplicate for each sample. Immunolocalization and phloroglucinol staining Approx. The sections were then washed two times with PBS stained with Calcofluor 0. All sections were scanned with the same settings.
The sections were placed in the drop of solution, incubated app. Measurement of acetyl bromide lignin The concentration of acetyl bromide lignin was determined according to the method described by [ 42 ]. After complete digestion, samples were cooled down and cleared by centrifugation. The lignin analysis was performed in triplicate for each sample.
Measurement of monolignol ratios and hydroxycinnamates by analytical pyrolysis The straw or entire shoots of mature plants were pyrolyzed in duplicates in random order.
Only total ion chromatogram TIC peak areas of compounds with no or insignificant co-elution were used in calculations. All compounds used for calculating monolignol and hydroxycinnamate ratios were identified by authentic standards or published mass spectra [ 44 ]. The compounds were grouped according to methoxylation into H, G or S. Monolignol ratios were calculated as the peak area of the specific monolignol in proportion to the total peak area of the three monolignols.
Analogously, the hydroxycinnamate ratio was calculated.
Pretreatments and enzymatic saccharification Pretreatments and enzymatic saccharification were performed on mature straw and entire shoot samples, following the method described by [ 39 ].
Dry material was ground and distributed using an automated sample preparation robotic system Labman Automation Ltd. The plates were sealed with Teflon tape with a little hole above each well, placed on a heating block and further sealed with a thin aluminium plate and a Teflon plate to ensure a gas tight enclosure.
As discussed below the loosening of cell wall polysaccharides seems to be very important under osmotic, drought or salt stress to maintain the possibility for cells and organs to expand.
This causes a cell wall loosening similar to the action of classical loosening enzymes like expansins or xyloglucan modifying enzymes Renew et al. The apparently contradicting observations about peroxidase activity under drought stress should be examined in broader sense, which considers all, peroxidase activity, substrates and ROS as a unit.
The balance between these factors may well explain the different results observed in plant studies with abiotic stress. An excess of peroxidase activity, cross-linkable substrates and sufficient amounts of H 2 O 2 will favor the local stiffening of the wall, reduce cell wall expansion and thus strengthen the mechanical stability of the cells and organs.
This will cause disruption of sugar polymers of the cell wall with a concomitant weakening in the mechanical properties of the wall Fry, Cho et al. The strong reduction in root length observed in control seedlings of Arabidopsis on salt-containing media is less pronounced if the CaXTH gene is expressed.
However, aberrant leaf morphology curled leaves was found in several independent lines and transverse sections of leaves showed an irregular cell pattern compared to wild type plants. The same CaXTH gene was later expressed in tomato plants without phenotypical side effects Choi et al.
Again the transgenic tomato seedlings showed a strongly increased salt tolerance with longer roots. The exact mode of action was not determined but the authors speculate about a beneficial cell wall strengthening of mesophyll cells, protecting them from excessive water loss. In addition, they suggest an important role of the XTH activity in remodeling the cell wall of stomata possibly preventing excess water loss.
Arabidopsis plants with a reduced level of cytokinin are more salt tolerant than the wild type. A transcriptome profiling identified numerous genes upregulated in the tolerant mutant, among them XTH genes and glycoside hydrolases Nishiyama et al.
Rice plants exposed to abiotic stress cold, heat, drought showed a strong increase in transcripts for OsXET9 , a xyloglucan modifying enzyme that might serve as a general stress marker gene Dong et al. Arabidopsis plants overexpressing a mannosephosphate reductase have increased levels of mannitol and are more tolerant to abiotic stress. Transcriptome analysis identified numerous cell wall modifying genes, which are upregulated in these plants among them xylosyltransferases involved in xyloglucan biosynthesis as well as XTH members.
The authors concluded that these genes are ineeded for cell growth and cell wall strengthening as a response to the accumulating mannitol Chan et al. Thus, many abiotic stress conditions lead to an increase in one or a few XTH genes.
Figure 1. The XTH gene family is classified according to Rose et al. Most but not all members are present on the Affimetrix ATH1 chip. The mutant has a surprisingly normal phenotype considering the attributed major role of xyloglucan for the stability of the primary cell wall. Biomechanical measurements however showed a reduced stiffness. One revised model comes to the conclusion that only a minor portion of the xyloglucan, which is not accessible to XTH enzymes, is involved in cellulose interaction.
Using a creep cell wall extension assay Park and Cosgrove showed that significant creep was only observed with glucanases which also cleave cellulose beside xyloglucan, suggesting that the tight connection must be modified for extension of the wall. This model however does not exclude the possibility that xyloglucan, which is at a given time point accessible for XTH, later becomes part of the inaccessible xyloglucan involved in the strong network with cellulose.
Expansin genes are also often transcriptionally upregulated by abiotic stress conditions. Motivated by such findings Han et al. Roots of overexpressor lines developed far better under high salt conditions than wild type tobacco seedlings. It was suggested that seedlings with increased expansin expression have a higher water retention ability, though the possible mechanism as well as the potential change in the cell walls remain unclear.
The overexpression of expansin A4 from rose in Arabidopsis leads to higher germination rates under salt stress, longer roots and an increase of lateral roots Lu et al. Furthermore, the overexpressing lines are more drought tolerant and recover after the stress, whereas all wild type plants died Dai et al. The gene was originally identified by the strong induction in rose petals undergoing dehydration.
Knockout of the Arabidopsis expansin like gene AtEXLA2 leads to plants with longer roots than the wild type under normal growth conditions but renders the roots to be more sensitive to salt stress Abuqamar et al.
This is in line with previous studies which suggest the necessity of a balanced expansin activity for normal cell growth and wall remodeling. Rice plants stop to elongate the internodial sections under drought stress leading to stunted plants. To unravel the process Todaka et al. The gene for OsPIL1 is down-regulated under drought.
They identified a number of target genes, including several expansin genes. GUS reporter gene construct they demonstrated a strong directly OsPil1-dependent induction of OsEXP4A by coexpression of the transcription factor in a rice protoplast system.
Ectopic expression of OsPIL1 leads to rice plants with long internodes, whereas repression of the gene results in very short plants suggesting that the coordinated expression of expanins among other genes is mainly responsible for internodial cell length and thus for plant height. In plants both, expansins and XTH, are present as a larger gene family with 35 members Lee et al. Figure 1 shows the relative expression rate of the whole gene family in control shoots and roots as well as under different abiotic stress conditions.
Note that not all members are represented on the ATH1-microarray chip. Only the dataset from Atgenexpress was used Kilian et al. The heat map shows that only a few members of each gene family respond to each stress factor and it also points to different responses in shoots and roots.
Growth of plant organs under stress is apparently a conflict between stiffening of cell walls by cross-linking and loosening them by ROS, expansins and XTH. A possible simplified model for growth under abiotic stress is presented in Figure 2. The frequently observed growth arrest under abiotic stress may be caused by cross-linking of glycoproteins and phenolics esterified with hemicellulose polymers.
This process requires ROS, the activity of peroxidases and substrates for the enzyme in balanced quantities. The cross-linking results in a dense network possibly preventing the undisturbed access of expansins and XTH to the xyloglucan substrate Figure 2B. If ROS production continues and all cross-linkable substrates are used up by previous peroxidase activity, elevated ROS-levels may cause radical mediated cleavage of polymer chains Figure 2C.
Figure 2. Model of growth of cell walls in unstressed conditions A , plants under abiotic stress showing growth arrest B , and tolerant plants overcoming the growth arrest by using ROS-mediated cleavage of cell wall polymers C see text for details. The pectins are often modified in plants exposed to drought stress. Leucci et al. The major finding was the increase in side chains of the pectic polymers rhamnogalacturonan I and II RGI and RGII , possibly because the pectins form hydrated gels which limit the damage to cells Leucci et al.
Furthermore, the biosynthesis of pectic polymers under drought stress was less affected in the tolerant cultivar Piro et al. A similar study with wheat seedlings comparing a drought sensitive with a tolerant line also showed more pectins in the tolerant cultivar, especially in young seedlings Konno et al.
A comparison of the cell wall composition of root tips from two soybean cultivars showed far higher levels of pectins in the salt tolerant cultivar than in the sensitive line, suggesting that the higher pectin content is beneficial for root growth under salt stress conditions An et al. Older plant material from two wheat cultivars with different salt tolerance was compared by Uddin et al.
Unesterified uronic acids increased upon salt stress in both cultivars. However, the increase in uronic acids in the salt tolerant cultivar was slower and stopped at a lower level compared to the sensitive line.
The method did not allow discriminating between galacturonic acid from pectins and glucuronic acid from the arabinoxylans. Thus, the exact change in the cell wall remains to be determined.
Rakszegi et al. The major finding was the increase in the dietary fiber arabinoxylan in all cultivars under both stress conditions. Frost tolerance of different Miscanthus genotypes is associated with compositional changes in the cell wall.
The amount of mixed-linked glycans strongly increases in all cultivars after cold acclimatization. The sum of galacturonic and glucuronic acid however increases in frost sensitive lines but decreases in the tolerant one.
All lines respond with a dramatic increase of cinnamyl alcohol dehydrogenase after cold acclimatization suggesting that enhanced lignification is associated with cold temperature treatment Domon et al. The changes in lignin content and composition caused by various stress factors was recently reviewed Magalhaes Silva Moura et al. Resurrection plants survive dehydration of their vegetative tissues to air dry state for extended periods and recover full metabolic competence upon rehydration Rascio and La Rocca, ; Moore et al.
The physiological changes have been studied intensively in some model resurrection plants like Craterostigma plantagineum or Xerophyta viscosa. Analysis of cell walls from resurrection plants either in the hydrated or the desiccated stage revealed species specific differences Moore et al. Upon desiccation several species have increased levels of arabinose, which are found in fractions associated with pectins and arabino-galactan-proteins.
High arabinan levels are also present in the cell wall of guard cells from Commelina communis Jones et al. A study with intact RG-I from potato clearly showed by NMR techniques, that arabinan side chains are hydrated faster than galactan side chains Larsen et al. Therefore, a high arabinan amount will readily rehydrate cell walls after drought.
Cell walls of seeds dry out during maturation and a number of seed cell walls also contain higher arabinan levels than the vegetative tissue Mosele et al. During germination the arabinan is largely metabolized and serves as a precursor for the synthesis of new wall polymers or arabino-galactan proteins upon activation to UDP-arabinose Gomez et al.
The high arabinan levels in seed cell walls as well as in desiccated resurrection plants has led to two conclusions. First of all, the arabinans likely fulfill a function as pectic plasticizers to keep the cell wall flexible under abiotic stress Moore et al. Second, the mechanism of high arabinan in cell walls from drying tissue is an invention of seeds which was later adopted by resurrection plants. Whether the plasticizer hypothesis fits for a broad variety of plants needs to be addressed in future.
An increase in arabinose for instance was not found in the resurrections plants Xerophyta viscosa or X. Arabidopsis mur-4 mutants in the enzyme UDP-xylose epimerase, which provides UDP-arabinose as a precursor for polymer synthesis, have extremely low levels of arabinose in their cell walls. However, mur-4 mutants show no visible changes in the phenotype, have viable seeds and a normal seed set Burget et al.
The perception of abiotic stress in the cell wall likely involves members of different receptor-like kinases, comprising a very large family of integral plasma membrane proteins. These receptor-like kinases are believed to perceive changes of the environment in the extracellular space and transmit their signal into the cell, using either second messengers, reactive oxygen species, interfering with abscisic acid signaling or by phosphorylating transcription factors or other unidentified signaling proteins Lindner et al.
Many of the genes for receptor-like kinases are induced by abiotic stress itself, thereby amplifying the signal for the necessary stress adaption response Lindner et al. A long known example for this is RPK1 from Arabidopsis. Constitutive expression of RPK1 causes an upregulation of a number of stress induced genes and results in an enhanced abiotic stress tolerance Osakabe et al. Furthermore, target genes of RPK1 are upregulated in a similar fashion by overexpression of RPK1 as observed by applying stress factors like drought, salt, cold, or heat.
The same RPK1 was recently identified as a major determinant for the regeneration frequency of shoots from Arabidopsis calli, a process that is unrelated to abiotic stress but may be linked to abscisic acid signaling Motte et al. This raises the question whether RPK1 is a primary receptor for abiotic stress or whether it is involved in transducing the stress signal. Unfortunately, the mechanism by which receptor-like kinases perceive the environmental stress remains to be elucidated.
A second group of cell wall integrity receptors is the CrRLK1 family originally identified in Catharanthus roseus. Reduced cell elongation phenotypes were also found for mutants in the1 and herk1 when both mutants were combined. Though CrRLK are primarily involved in controlling cell wall integrity under normal physiological conditions, they might provide a framework for the control of cell walls under abiotic stress.
For the formation of localized lignin deposition in the Casparian stripe an interaction of peroxidases and superoxide producing NADPH-oxidases was shown recently Lee et al. Boron is an essential plant micronutrient required for cross-linking side chains of pectin RGII. It forms diesters between apiose residues Ishii et al. Boron deficiency in crop plants is associated with an increase in thickness of the cell wall often referred to as the swollen cell wall phenotype. Thus, the increase in thickness is not caused by deposition of more carbohydrate polymers but by an increase of the pore size of the cell wall Fleischer et al.
A similar phenotype is observed in plants which have a reduced availability of UDP-apiose and thus less side chains in RGII, though the boron availability is normal Ahn et al. Plants grown under limiting boron concentrations are frequently observed on soils with high rain falls, which leach out the boric acid released from rocks. They exhibit pleiotropic phenotypes like inhibition of growth, damage in xylem vessels, and disturbance of plasma membrane transport processes covered by recent reviews Camacho-Cristobal et al.
In an attempt to dissect the response Koshiba et al. Within 12 h of boron deficiency the first cells undergo programmed cell death accompanied by the production of ROS and lipid break down products Koshiba et al. This suggests that the drastic change in cell wall architecture activates the cell wall quality control system to a level which promotes programmed cell death as a response. Boron needs to be present in an optimal concentration because too high levels of boron are phytotoxic.
This observation was recently addressed by the finding that normal boron levels also cross-link glycosylinositol phosphorylceramides of the plasma membrane with arabinogalactan proteins of the cell wall, thereby attaching the membrane to the cell wall Voxeur and Fry, High concentrations of boron disrupt this interaction which may explain the phytotoxicity of high levels of boron. The many phenotypes observed with either too low or too high concentrations of boron have stimulated a discussion that proposes a signaling function for boron Goldbach and Wimmer, ; Gonzalez-Fontes et al.
Plants grown under boron deficiency will likely activate a part of the cell wall integrity control system, which might then activate signaling pathways indirectly observed as boron mediated signaling.
The cell wall is clearly affected by many abiotic stress conditions. Most data come from transcriptome analysis rather than biochemical experiments. The balance between the formation of ROS and the transcriptional changes for cell wall remodeling enzymes seems to be important for the outcome, either growth arrest in salt and drought sensitive cultivars or a continuation of preferentially root growth, though with a reduced rate.
Surprisingly little is known about changes in the cell wall itself, a challenge for a better understanding of abiotic stress tolerance. The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. The funding of the publication cost for this article by the open access fond of Salzburg University is gratefully acknowledged.
Abuqamar, S. A mutation in the expansin-like A2 gene enhances resistance to necrotrophic fungi and hypersensitivity to abiotic stress in Arabidopsis thaliana.
Plant Pathol. Ahn, J. An, P. Effects of NaCl on root growth and cell wall composition of two soya bean cultivars with contrasting salt tolerance. Crop Sci. Atkinson, N. The interaction of plant biotic and abiotic stresses: Braidwood, L. Mybody is a cage: New Phytol.