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1.
Previous mechanical studies using algae have concentrated on cell extension and growth using creep-type experiments, but
there appears to be no published study of their failure properties. The mechanical strength of single large internode cell
walls (up to 2 mm diameter and 100 mm in length) of the charophyte (giant alga) Chara corallina was determined by dissecting cells to give sheets of cell wall, which were then notched and fractured under tension. Tensile
tests, using a range of notch sizes, were conducted on cell walls of varying age and maturity to establish their notch sensitivity
and to investigate the propagation of cracks in plant cell walls. The thickness and stiffness of the walls increased with
age whereas their strength was little affected. The strength of unnotched walls was estimated as 47 ± 13 MPa, comparable to
that of some grasses but an order of magnitude higher than that published for model bacterial cellulose composite walls. The
strength was notch-sensitive and the critical stress intensity factor K
1c was estimated to be 0.63 ± 0.19 MNm−3/2, comparable to published values for grasses.
Received: 4 April 2000 / Accepted: 21 July 2000 相似文献
2.
To study the function of xyloglucan endotransglycosylase (XET) in vivo we isolated, a tomato (Lycopersicon esculentum Mill.) XET cDNA (GenBank AA824986) from the homologous tobacco (Nicotiana tabacum L.) clone named NtXET-1 (Accession no. D86730). The expression pattern revealed highest levels of NtXET-1 mRNA in organs highly enriched in vascular tissue. The levels of NtXET-1 mRNA decreased in midribs with increasing age of leaves. Increasing leaf age was correlated with an increase in the
average molecular weight (MW) of xyloglucan (XG) and a decrease in the relative growth rates of leaves. Transgenic tobacco
plants with reduced levels of XET activity were created to further study the biochemical consequences of reduced levels of
NtXET-1 expression. In two independent lines, total XET activity could be reduced by 56% and 37%, respectively, in midribs of
tobacco plants transformed with an antisense construct. The decreased activity led to an increase in the average MW of XG
by at least 20%. These two lines of evidence argue for NtXET-1 being involved in the incorporation of small XG molecules into the cell wall by transglycosylation. Reducing the incorporation
of small XG molecules will result in a shift towards a higher average MW. The observed reduction in NtXET-1 expression and increase in the MW of XG in older leaves might be associated with strengthening of cell walls by reduced
turnover and hydrolysis of XG.
Received: 24 January 2000 / Accepted: 21 July 2000 相似文献
3.
Kylie J. Nunan Ian M. Sims Antony Bacic Simon P. Robinson Geoffrey B. Fincher 《Planta》1997,203(1):93-100
Cell walls have been isolated from the mesocarp of mature grape (Vitis vinifera L.) berries. Tissue homogenates were suspended in 80% (v/v) ethanol to minimise the loss of water-soluble wall components
and wet-sieved on nylon mesh to remove cytoplasmic material. The cell wall fragments retained on the sieve were subsequently
treated with buffered phenol at pH 7.0, to inactivate any wall-bound enzymes and to dislodge small amounts of cytoplasmic
proteins that adhered to the walls. Finally, the wall preparation was washed with chloroform/methanol (1:1, v/v) to remove
lipids and dried by solvent exchange. Scanning electron microscopy showed that the wall preparation was essentially free of
vascular tissue and adventitious protein of cytoplasmic origin. Compositional analysis showed that the walls consisted of
approximately 90% by weight of polysaccharide and less than 10% protein. The protein component of the walls was shown to be
rich in arginine and hydroxyproline residues. Cellulose and polygalacturonans were the major constituents, and each accounted
for 30–40% by weight of the polysaccharide component of the walls. Substantial varietal differences were observed in the relative
abundance of these two polysaccharides. Xyloglucans constituted approximately 10% of the polysaccharide fraction and the remainder
was made up of smaller amounts of mannans, heteroxylans, arabinans and galactans.
Received: 26 November 1996 / Accepted: 30 January 1997 相似文献
4.
Summary The origin of a cell wall was an event of fundamental importance in the evolution of plants. In the green algae, cell walls apparently had independent origins in at least three lines of evolution. In this paper, the components of the cell wall were determined and compared in four filamentous green algae representing the charophycean, chlorophycean and ulvacean evolutionary lines. The walls of all four have hydroxyproline-containing proteins which separate into five or six bands upon SDS gel electrophoresis. Variation does exist, with the charophyte possessing fast moving electrophoretic bands and high hydroxyproline content, the chlorophytes having intermediate movement of bands and lower hydroxyproline content, and the ulvacean representative possessing slow moving bands and a very low, if not questionable, hydroxyproline and saccharide content. Qualitative and quantitative estimates of wall proteins and sugars have been determined and compared. A hypothetical scheme of cell wall evolution based on these data, those of previous analyses, and recent phylogenetic schemes is presented. Although sound conclusions cannot be made until more information is available, the scheme might help to emphasize the areas most in need of additional research.This work was supported by National Science Foundation Grant DEB 78-03554. 相似文献
5.
Changes in the limiting porosity of cell walls, i.e. the size limit for permeation of neutral molecules through the wall,
were studied in several higher-plant cell-suspension cultures. For this purpose, samples of biomass fixed at different cultivation
times were investigated using a method based on size-exclusion chromatography of polydisperse dextrans before and after equilibration
with the extracted cell clusters. In suspension cultures of Chenopodium album L., Dioscorea deltoidea Wall. and Medicago sativa L., the mean size limit (MSL; critical Stokes' radius for exclusion of neutral polymers from half of the intracellular space)
was found to vary between 2.4 and 3.8 nm. It decreased significantly during transition from the growth phase to the stationary
phase. In the case of the C. album culture this change was found to be irrespective of whether sucrose in the medium was completely depleted at the end of the
growth phase or not. The MSL was kept constant for long periods of the stationary phase if cell viability was maintained by
repeated sucrose supplement. In a suspension strain of Triticum aestivum L., the MSL of cell wall permeation was comparatively small (1.75 nm) and remained constant during all cultivation phases.
Relations between limiting porosity and cell wall growth, loss of pectic compounds to the medium, cross-linking activities
and cell wall stiffening are discussed.
Received: 19 December 1996 / Accepted: 23 April 1997 相似文献
6.
Transfer cell wall architecture: a contribution towards understanding localized wall deposition 总被引:1,自引:0,他引:1
Summary. A survey is presented of the architecture of secondary wall ingrowths in transfer cells from various taxa based on scanning
electron microscopy. Wall ingrowths are a distinguishing feature of transfer cells and serve to amplify the plasma membrane
surface area available for solute transport. Morphologically, two categories of ingrowths are recognized: reticulate and flange.
Reticulate-type wall ingrowths are characterized by the deposition of small papillae that emerge from the underlying wall
at discrete but apparently random loci, then branch and interconnect to form a complex labyrinth of variable morphology. In
comparison, flange-type ingrowths are deposited as curvilinear ribs of wall material that remain in contact with the underlying
wall along their length and become variously elaborate in different transfer cell types. This paper discusses the morphology
of different types of wall ingrowths in relation to existing models for deposition of other secondary cell walls.
Received July 20, 2001 Accepted November 29, 2001 相似文献
7.
8.
Isolated cell walls of mature Chlorella fusca consisted of about 80% carbohydrate, 7% protein, and 13% unidentified material. Mannose and glucose were present in a ratio of about 2.7:1 and accounted for most of the carbohydrate. Minor components were glucuronic acid, rhamnose, and traces of other sugars; galactose was absent. After treatment with 2 M trifluoroacetic acid or with 80% acetic acid/HNO3 (10/1, v/v), a residue with a mannose/glucose ratio of 0.3:1 was obtained, probably representing a structural polysaccharide. An X-ray diffraction diagram of the walls showed one diffuse reflection at 0.44 nm and no reflections characteristic of cellulose. Walls from young cells contained about 51% carbohydrate, 12% protein, and 37% unidentified material. Mannose and glucose were also the main sugars; their absolute amounts per wall increased 6–7 fold during cell growth. Walls isolated with omission of a dodecylsulphate/mercaptoethanol/urea extraction step had a higher protein content and, with young walls, a significantly higher glucose and fucose content. These data and other published cell wall analyses show a wide variability in cell wall composition of the members of the genus Chlorella.Abbreviations GLC
gas liquid chromatography
- TFA
trifluoroacetic acid 相似文献
9.
Blee KA Wheatley ER Bonham VA Mitchell GP Robertson D Slabas AR Burrell MM Wojtaszek P Bolwell GP 《Planta》2001,212(3):404-415
10.
Atomic force microscopy (AFM) was used to image celery (Apium graveolens L.) parenchyma cell walls in situ. Cellulose microfibrils could clearly be distinguished in topographic images of the cell
wall. The microfibrils of the hydrated walls appeared smaller, more uniformly distributed, and less enmeshed than those of
dried peels. In material that was kept hydrated at all times and imaged under water, the microfibril diameter was mainly in
the range 6–25 nm. The cellulose microfibril diameters were highly dependent on the water content of the specimen. As the
water content was decreased, by mixing ethanol with the bathing solution, the microfibril diameters increased. Upon complete
dehydration of the specimen we observed a significant increase in microfibril diameter. The procedure used to dehydrate the
parenchyma cells also influenced the size of cellulose microfibrils with freeze-dried material having larger diameters than
air-dried material.
Received: 16 November 1999 / Accepted: 7 March 2000 相似文献
11.
The gross composition of the outer epidermal cell wall from third internodes of Pisum sativum L. cv. Alaska grown in dim red light, and the effect of auxin on that composition, was investigated using interference microscopy. Pea outer epidermal walls contain as much cellulose as typical secondary walls, but the proportion of pectin to hemicellulose resembles that found in primary walls. The pectin and hemicellulose fractions from epidermal peels, which are enriched for outer epidermal wall but contain internal tissue as well, are composed of a much higher percentage of glucose and glucose-related sugars than has been found previously for pea primary walls, similar to non-cellulosic carbohydrate fractions of secondary walls. The epidermal outer wall thus has a composition rather like that of secondary walls, while still being capable of elongation. Auxin induces a massive breakdown of hemicellulose in the outer epidermal wall; nearly half the hemicellulose present is lost during 4 h of growth in the absence of exogenous sugar. The percentage breakdown is much greater than has been seen previously for whole pea stems. It has been proposed that a breakdown of xyloglucan could be the basis for the mechanical loosening of the outer wall. This study provides the first evidence that such a breakdown could be occurring in the outer wall.M.S. Bret-Harte would like to thank Dr. Peter M. Ray, of Stanford University, for helpful discussions and for technical and editorial assistance, Dr. Winslow R. Briggs, of the Camegie Institude of Washington, for the use of experimental facilities and for helpful discussions, Dr. Wendy K. Silk, of the University of California, Davis, for helpful discussions and financial support, Dr. Paul B. Green for financial support, and Drs. John M. Labavitch and L.C. Greve, of the University of California, Davis, for performing the -cellulose analysis on short notice, in response to a request by an anonymous reviewer. This work was supported by a National Science Foundation Graduate Fellowship to M.S. B.-H., National Science Foundation Grant DCB8801493 to Paul B. Green, and the generosity of Wendy K. Silk (Department of Land, Air, and Water Resources, University of California, Davis) during the final writing. 相似文献
12.
In vivo and in vitro swelling of cell walls during fruit ripening 总被引:17,自引:0,他引:17
Robert J. Redgwell Elspeth MacRae Ian Hallett Monica Fischer Jo Perry Roger Harker 《Planta》1997,203(2):162-173
Swelling properties of the cell walls of nine temperate fruit species, selected for their different ripening and textural
characteristics, were studied during ripening. Cell wall swelling was examined in intact fruit using microscopy techniques
and in vitro, using cell wall material isolated from fruit tissue. In fruit which ripened to a soft melting texture (persimmon,
avocado, blackberry, strawberry, plum), wall swelling was pronounced, particularly in vitro. In-vivo swelling was marked only
in avocado and blackberry. Fruit which ripened to a crisp, fracturable texture [apple (two cultivars), nashi pear, watermelon]
did not show either in-vivo or in-vitro swelling of the cell wall. There was a correlation between swelling and the degree
of pectin solubilisation, suggesting that wall swelling occurred as a result of changes to the viscoelastic properties of
the cell wall during pectin solubilisation. Chemical and enzymatic removal of pectin from kiwifruit cell wall material supported
the idea that swelling is associated with movement of water into voids left in the cellulose-hemicellulose network by the
solubilised pectin. However, the results also suggested that swelling in vivo was more complex than this, and that the physicochemical
changes which led to swelling included other elements of cell wall modification involving the site and mechanism of pectin
solubilisation and-or the cellulose-xyloglucan complex.
Received: 28 January 1997 / accepted: 11 March 1997 相似文献
13.
Plastic and elastic in-vitro extensibilities (E
pland E
el
) of cell walls from growing maize (Zea mays L.) coleoptile segments were measured by stretching frozen-thawed tissue, pre-extended to its in-vivo length, at constant force (creep test) in a custom-buildt extensiometer, equipped with a linear-displacement transducer. The indole-3-acetic acid (IAA)-induced change of E
pl
(E
pl
) is strictly correlated with the growth rate for a period of 3–4 h. Subsequently, E
plremains constant while the growth rate is slowing down. Since this discrepancy can be accounted for by a growth-dependent reduction of osmotic pressure, it is concluded that E
plrepresents quantitatively the relative increase of in-vivo extensibility (cell wall loosening) involved in IAA-mediated cell growth over a much longer time. On the other side it is argued that the growth rate may not be strictly correlated with wall extensibility during long-term growth. Abscisic acid (ABA) inhibits segment growth induced by auxin, fusicoccin, or exogenous acid, and this effect can be quantitatively attributed to an ABA-mediated reduction of cell wall extensibility as determined by the E
plmeasurement. Both, IAA and ABA have no effect on total protein synthesis, RNA synthesis, and amount of osmotic solutes. Fusicoccin-induced proton excretion is only slightly inhibited by ABA. In contrast to ABA, growth inhibition by cycloheximide (CHI) is always much larger than the concomitant reduction of E
pl
, indicating that a further growth parameter is also involved in the inhibition of cell growth by CHI. E
el
is not affected by either IAA, ABA, or CHI. It is concluded that E
pl
as determined by the applied method, represents a relative measure of the actual in-vivo extensibility of the growing cell wall at the very moment when the tissue is killed, rather than an average extensibility accumulated over some immediate-past period of time as suggested by Cleland (1984, Planta 160, 514–520). Hence, we further draw the conclusion that IAA and ABA control of cell growth can entirely be attributed to a modulation of cell wall extensibility by these hormones in maize coleoptiles.Abbreviations ABA
±abscisic acid
- CHI
cycloheximide
-
E
el
, Epl
elastic and plastic in vitro extensibilities, respectively (E
el+Epl=Etot>)
- FC
fusicoccin
- IAA
indole-3-acetic acid 相似文献
14.
The relationship between xyloglucan endotransglycosylase and in-vitro cell wall extension in cucumber hypocotyls 总被引:14,自引:0,他引:14
Simon J. McQueen-Mason Stephen C. Fry Daniel M. Durachko Daniel J. Cosgrove 《Planta》1993,190(3):327-331
It has been proposed that cell wall loosening during plant cell growth may be mediated by the endotransglycosylation of load-bearing polymers, specifically of xyloglucans, within the cell wall. A xyloglucan endotransglycosylase (XET) with such activity has recently been identified in several plant species. Two cell wall proteins capable of inducing the extension of plant cell walls have also recently been identified in cucumber hypocotyls. In this report we examine three questions: (1) Does XET induce the extension of isolated cell walls? (2) Do the extension-inducing proteins possess XET activity? (3) Is the activity of the extension-inducing proteins modulated by a xyloglucan nonasaccharide (Glc4-Xyl3-Gal2)? We found that the soluble proteins from growing cucumber (cucumis sativum L.) hypocotyls contained high XET activity but did not induce wall extension. Highly purified wall-protein fractions from the same tissue had high extension-inducing activity but little or no XET activity. The XET activity was higher at pH 5.5 than at pH 4.5, while extension activity showed the opposite sensitivity to pH. Reconstituted wall extension was unaffected by the presence of a xyloglucan nonasaccharide (Glc4-Xyl3-Gal2), an oligosaccharide previously shown to accelerate growth in pea stems and hypothesized to facilitate growth through an effect on XET-induced cell wall loosening. We conclude that XET activity alone is neither sufficient nor necessary for extension of isolated walls from cucumber hypocotyls. 相似文献
15.
Electron-energy-loss spectroscopic imaging of calcium and nitrogen in the cell walls of apple fruits 总被引:5,自引:0,他引:5
I. Max Huxham Michael C. Jarvis Lynette Shakespeare Colin J. Dover David Johnson J. Paul Knox Graham B. Seymour 《Planta》1999,208(3):438-443
Changes in texture are an integral part of ripening in most fleshy fruits and these changes are thought to be determined,
primarily, by alterations in cell wall structure. Electron energy loss spectroscopy (EELS) imaging was used to obtain quantitative
information on the levels of calcium and nitrogen in the cell walls of apple (Malus domestica Borkh. cv. Cox's Orange Pippin) fruits. Samples of fruit cortex were prepared for EELS by high-pressure freezing and molecular
distillation drying to minimize loss and redistribution of soluble cell wall components such as calcium. The EELS imaging
successfully resolved calcium and nitrogen levels in the middle lamella and primary cell wall. When the elemental compositions
of the cell walls of Cox's apples from two sites in the UK were compared at harvest or after 6 months storage, the orchard
which always produced consistently firmer fruit had significantly lower levels of cell wall calcium and higher levels of cell
wall nitrogen. This result was unexpected since firm texture in apples and other fruits has been commonly associated with
elevated levels of fruit calcium. The nitrogen-rich material in the sections used for EELS was insoluble in acidified methanol,
indicating that it represented a high-molecular-weight component in the cell wall. Furthermore, total tissue hydroxyproline
levels were greatest in material with elevated cell wall nitrogen, suggesting enhanced levels of wall structural proteins
in the tissue. These data indicate a correlation between increased amounts of cell wall nitrogen and firm fruit texture. The
possible role of cell wall proteins in determining the textural properties of fruit tissue is discussed.
Received: 19 November 1998 / Accepted: 28 January 1999 相似文献
16.
Maria Laurenzi Giuseppina Rea Rodolfo Federico Paraskevi Tavladoraki Riccardo Angelini 《Planta》1999,208(2):146-154
17.
Comparison between maize root cells and their respective regenerating protoplasts: wall polysaccharides 总被引:1,自引:0,他引:1
The cell-wall polysaccharides from different parts of maize roots have been analysed. The arabinose, galactose and mannose contents are influenced by cell differentiation, whereas xylose, rhamnose and uronic-acid contents are not. In cap cells, the pectin content is low but rhamnose and fucose are present in larger quantities. The cell-wall polysaccharides from cells of the elongation zone and their respective regenerating protoplasts were also analysed. The walls of the protoplasts contained higher xylose and mannose levels and a much lower level of cellulose than the cells from which they were derived. 相似文献
18.
Background and Aims
In seed plants, the ability of guard cell walls to move is imparted by pectins. Arabinan rhamnogalacturonan I (RG1) pectins confer flexibility while unesterified homogalacturonan (HG) pectins impart rigidity. Recognized as the first extant plants with stomata, mosses are key to understanding guard cell function and evolution. Moss stomata open and close for only a short period during capsule expansion. This study examines the ultrastructure and pectin composition of guard cell walls during development in Funaria hygrometrica and relates these features to the limited movement of stomata.Methods
Developing stomata were examined and immunogold-labelled in transmission electron microscopy using monoclonal antibodies to five pectin epitopes: LM19 (unesterified HG), LM20 (esterified HG), LM5 (galactan RG1), LM6 (arabinan RG1) and LM13 (linear arabinan RG1). Labels for pectin type were quantitated and compared across walls and stages on replicated, independent samples.Key Results
Walls were four times thinner before pore formation than in mature stomata. When stomata opened and closed, guard cell walls were thin and pectinaceous before the striated internal and thickest layer was deposited. Unesterified HG localized strongly in early layers but weakly in the thick internal layer. Labelling was weak for esterified HG, absent for galactan RG1 and strong for arabinan RG1. Linear arabinan RG1 is the only pectin that exclusively labelled guard cell walls. Pectin content decreased but the proportion of HG to arabinans changed only slightly.Conclusions
This is the first study to demonstrate changes in pectin composition during stomatal development in any plant. Movement of Funaria stomata coincides with capsule expansion before layering of guard cell walls is complete. Changes in wall architecture coupled with a decrease in total pectin may be responsible for the inability of mature stomata to move. Specialization of guard cells in mosses involves the addition of linear arabinans. 相似文献19.
Characterization of long-term extension of isolated cell walls from growing cucumber hypocotyls 总被引:24,自引:0,他引:24
Daniel J. Cosgrove 《Planta》1989,177(1):121-130
Walls from frozen-thawed cucumber (Cucumis sativus L.) hypocotyls extend for many hours when placed in tension under acidic conditions. This study examined whether such creep is a purely physical process dependent on wall viscoelasticity alone or whether enzymatic activities are needed to maintain wall extension. Chemical denaturants inhibited wall creep, some acting reversibly and others irreversibly. Brief (15 s) boiling in water irreversibly inhibited creep, as did pre-incubation with proteases. Creep exhibited a high Q10 (3.8) between 20° and 30°C, with slow inactivation at higher temperatures, whereas the viscous flow of pectin solutions exhibited a much lower Q10 (1.35). On the basis of its temperature sensitivity, involvement of pectic gel-sol transitions was judged to be of little importance in creep. Pre-incubation of walls in neutral pH irreversibly inactivated their ability to creep, with a half-time of about 40 min. At 1 mM, Cu2+, Hg2+ and Al3+ were strongly inhibitory whereas most other cations, including Ca2+, had little effect. Sulfhydryl-reducing agents strongly stimulated creep, apparently by stabilizing wall enzyme(s). The physical effects of these treatments on polymer interactions were examined by Instron and stress-relaxation analyses. Some treatments, such as pH and Cu2+, had significant effects on wall viscoelasticity, but others had little or no apparent effect, thus implicating an enzymatic creep mechanism. The results indicate that creep depends on relatively rugged enzymes that are firmly attached to or entangled in the wall. The sensitivity of creep to SH-reducing agents indicates that thiol reduction of wall enzymes might provide a control mechanism for endogenous cell growth.Abbreviations DTT
dithiothreitol
- EDTA
ethylenediaminetetraacetic acid
- EGTA
ethyleneglycol-bis-(-aminoethylether)-N,N,N,N-tetraacetic acid
- Hepes
N-2-hydroxyethylpiperazine-N-2-ethansulfonic acid 相似文献
20.
The process of division was investigated in the different types of plastids found in the tip cell of the protonema of Funaria hygrometrica Sibth. There were no structural changes in the envelope membranes of any of the plastid types during the initial stage of division. As the process of constriction advanced, thylakoids were locally disintegrated and sometimes starch grains in the isthmus were locally dissolved. In the isthmus, tightly constricted plastids were characterized by an undulating envelope and an increasing number of vesicles. After three-dimensional reconstruction of electronmicrographs a distinct filamentous structure was observed in the plane of division outside the plastid but close to the envelope. At different stages of division the constricted regions were partly surrounded by one or a few filaments. The roundish plastids in the apical zone were accompanied by single microtubule bundles, and the spindle-shaped plastids in the cell base were surrounded by single microtubules and microtubule bundles. A model of co-operation between microtubules and the filamentous structure in the division process is discussed.A preliminary report was presented at the Tagung der Deutschen Botanischen Gesellschaft und der Vereinigung für Angewandte Botanik, Hamburg, September 1986 相似文献