Changes In Cell Wall Properties Research Articles

Increased Cell-Wall Mass and Resistance to Freezing and Snow Mold during Cold Acclimation of Winter Wheat under Field Conditions

Accumulation of soluble carbohydrates plays an important role in enhancement of resistance to freezing and snow mold of plants during cold acclimation. Nevertheless, few studies have examined whether changes in cell wall properties are involved in enhancement of resistance during cold acclimation. In this study, four winter wheat cultivars were sown in a field on six different dates during August–October, and their resistance to freezing and snow mold were compared in relation to soluble carbohydrate content and cell-wall mass in leaves. Resistance to freezing and snow mold was much higher in the plants sown on 23 September than in those sown on 9 September. The percentage of cell-wall mass in leaf to total dry mass (%CW) and water-soluble carbohydrate content also increased considerably during 9–23 September. Multiple regression analyses revealed that %CW contributed significantly to freezing resistance, whereas total water-soluble carbohydrate content contributed significantly to snow mold resistance. These results suggest that increased %CW enhances freezing resistance during cold acclimation.

Changes in the geometry of the apical meristem and concomitant changes in cell wall properties during photoperiodic induction of flowering in Chenopodium rubrum.

• A putative role for local forces at the surface of the apical meristem for plant organogenesis has been postulated in various studies. To correlate changes in morphogenesis to altered local forces, we followed the geometry of the apical meristem during photoperiodic flower induction in Chenopodium rubrum. • The shape of the apical meristem was determined using cryo-scanning electron microscopy. Cell wall properties on the surface of the dome were visualized using uplight polarization microscopy. • A subtle depression at the summit of the apical dome, typical for the vegetative state, became rounded during the early phase of flower induction. The observed changes were quantified as an increase in the ratio of height to diameter of the dome. In parallel, the properties of cell walls on the surface of the dome changed. • The changes in geometry of the apical meristem were attributed to water movement in the meristem paralleled by a change in cell wall properties at the top of the dome. The results support the hypothesis that local changes in surface tension precede initiation of organ primordia.

Expansin gene expression in Datura ferox L. seeds is regulated by the low-fluence response, but not by the high-irradiance response, of phytochromes

Expansins are a multi-gene family of proteins involved in changes in cell wall properties. In seeds where the embryo is completely surrounded by the endosperm, dormancy breakage requires weakening of the micropylar endosperm, increased embryo growth potential or both. Cell wall alterations are fundamental components of these processes, and expansins are thought to participate in them. Here, we explore the possible involvement of expansins in the control of germination by phytochrome in Datura ferox L. seeds. Based on the conserved sequences of known expansin genes, corresponding primers were designed to investigate the expression of expansin mRNAs by reverse transcriptase polymerase chain reaction (RT-PCR). One expansin mRNA was detected in micropylar endosperm of D. ferox, while two mRNAs were present in the embryo prior to radicle emergence. Expansin transcript content is promoted by red (R) light, both in the micropylar endosperm and the embryo; these effects of R are far-red light (FR) reversible, displaying a typical low-fluence response (LFR) in a way fully consistent with the photocontrol of germination. On the other hand, when the promotion of germination by the LFR is antagonized by exposing the seeds to continuous FR through a high-irradiance response (HIR) or by ABA, the inhibitory treatments do not affect expansin mRNA abundance. The results support the participation of expansins in the promotion of germination by LFR of phytochromes, and suggest that inhibition of germination by HIR or ABA does not include a reduction in the transcription of expansin genes.

Changes in cell-wall properties of wheat (Triticum aestivum) roots during aluminum-induced growth inhibition.

The effects of aluminum (Al) on root elongation, the mechanical extensibility of the cell wall, and the amount of cell-wall polysaccharides in the roots of Al-resistant (Atlas 66) and Al-sensitive (Scout 66) cultivars of wheat (Triticum aestivum L.) were examined. Exposure to 10 &mgr;M AlCl3 for 6 h inhibited root elongation in Scout 66 but not in Atlas 66. It also decreased the mechanical extensibility of the cell wall in the roots of both cultivars, but prominently only in the roots of Scout 66. The amount of hemicellulose in the 10-mm region of root apex of Scout 66 was increased by the exposure to Al, especially in the apical regions. Al did not influence the neutral sugar composition of either pectin or hemicellulose in Scout 66 roots. However, Al increased the weight-average molecular mass of hemicellulosic polysaccharides and the amounts of wall-bound ferulic and diferulic acids in Scout 66 roots. These findings suggest that Al modifies the metabolism of cell-wall components and thus makes the cell wall thick and rigid, thereby inhibiting the growth of wheat roots.

Lipid profiles of Helicobacter pylori colony variants.

A phase variation in Helicobacter pylori has been previously described. In one phase the bacterium had a cell wall lipid content typical for gram-negative bacteria (HpL), whereas in the other phase the bacterium was found to have a cell wall with increased amounts of lysophospholipids (HpS). The conversion is spontaneous, but could also be induced by acid (HpS(ind)) and was associated with in vitro release of Vac A and urease. The purpose of the present study was to determine the full phospholipid content of the cell wall to indicate a molecular mechanism of the colony variation. There were no appreciable differences between the lipid profiles of HpS and HpS(ind), while there were major differences between HpL and the S-variant. In the S-variant, lysophospholipids constituted about 50% of the total phospholipids, as compared to less than 2% in the L-variant. The proportion of total and individual cholesteryl glucosides also showed considerable changes. HpL was dominated by the phosphate-linked cholesteryl glucoside (72%) while the acylated cholesteryl glucoside was the main cholesteryl glucoside of the S-variant (65%). Our results demonstrate a dramatic change in cell wall properties after acid induction and spontaneously in vitro, and suggest some molecular mechanisms for this variation from an in vitro non-virulent to a virulent variant.

Control of leaf expansion in sunflower (Helianthus annuusL.) by nitrogen nutrition

Seedlings of Helianthus annuus L. were grown at an initially high relative nitrate supply rate (0.27 mol N mol N–1 d–1). The supply was subsequently reduced to a low rate (0.04 mol N mol N–1 d–1). The response of leaf area development to this abrupt decrease in nitrate availability was characterized by following the expansion of the primary and secondary leaf pairs. The timing of the drop in nitrate supply was when cell division in the epidermis of the primary leaf pair was largely complete. Reducing the availability of nitrate had a strong effect on leaf area expansion. The final leaf size of the primary leaf pair was affected indicating an effect of nitrate availability on cell expansion. By the end of the experiment the secondary leaf pair was only one-third the area of that on control seedlings. The role of epidermal cell turgor pressure in this growth response was assessed by direct measurements with a miniature cell pressure probe. No reduction in cell turgor pressure following the decrease in nitrate availability was detected. It is concluded that a reduction in turgor pressure was not responsible for the reduction in leaf area expansion and it is suggested that reduced cell expansion was due to changes in cell wall properties. Concentrations of leaf and root abscisic acid increased following the reduction in nitrate availability.

Stimulation and inhibition of pine root growth by osmotic stress

summaryThe effect of osmotic stress on the regulation of extension of roots of pine seedlings (Pinus pinaster Ait.) was studied. Extension rate (r) was measured as increase in root length, and as local growth rate (LGR) along the growing region. Turgor pressure (P) was measured over the same profile using the cell pressure probe. Correlation of LGR and P allowed changes in cell wall mechanical properties to be followed.In unstressed plants, differences in LGR along the root apex were owing to variations in the mechanical properties of the cell walls since P remained constant at 0.5 MPa along the first 10 mm of the root tip. Contrary to expectation, a moderate water stress of 0.15 MPa stimulated root growth despite a small reduction in P to 0.4 MPa. The walls of the expanding cells became looser, allowing enhanced growth in spite of reduced turgor. Examination of LGR showed that these changes occurred uniformly over the whole elongation zone. The advantage to the plant of this is discussed. Higher stresses (0.45 and 0.66 MPa) decreased cell turgor to a greater degree (≤0.3 MPa) and decreased growth rate. At the highest stress (0.66 MPa), P was maximal in cells that were still elongating, resulting in a longitudinal gradient in turgor. In both treatments LGR remained unchanged at the apex of the growing zone. Wall loosening appeared to have occurred in this region. Pine root extension is therefore modulated by changes in cell wall properties, with cell wall loosening resulting in increased growth at moderate stress. It appears that growth under higher stresses is limited by inability to maintain turgor.

The control of cell expansion in roots.

The expansion of roots is considered at the level of the single cell. The water relations of cell expansion are discussed. Water entry, solute import and cell wall properties are considered as possible regulatory points. It is argued that root cell expansion can be understood in terms of cell turgor pressure and the physical properties of the cell wall, provided solute supply is not limiting. Various measurements of cell wall properties in roots are presented and the assumptions underlying their measurements are presented. It is concluded that cell wall properties must be measured over short time periods to prevent alterations in wall properties during the experiment. The radial location of the load-bearing layers is discussed and it is concluded that, unlike aerial tissue, growth is limited by the properties of the inner layer of the root cortex. Evidence is presented to show that cell wall properties can change both during development and following turgor perturbation. In general, however, turgor itself is tightly regulated, particularly towards the root tip. A number of environmental situations are presented in which root growth is altered. The mechanism of the alteration is discussed at the single cell level. These 'stresses'include osmotic stress, low temperature and soil compaction. In many cases the alteration of root growth is consistent with changes in the ceil wall properties of the growing ceils. Severe stress, resulting in near cessation of root cell extension, can result in a change (usually an increase) in turgor pressure. The change in turgor pressure of the cells in the growing zone is smaller than that which would be expected from a continuation of an unstressed solute import rate. This exemplifies both the change in cell wall properties and the tight turgor homeostasis of root tips. The biochemical processes which underlie the modulation of cell wall properties are presented as they are currently understood in roots. Measurements of the chemical composition of the wall have not revealed any useful differences which can explain the developmental or stress-induced changes in cell wall properties. Recent work on cell wall enzymes and proteins may provide information about control of cross-linkages within the wall. In the last section the relative importance of apoplastic and symplastic solute transport to the expanding cells is considered. At present the consensus appears to favour the symplastic route, but the apoplastic pathway may also operate, possibly as a scavenging mechanism for leaked ions. The regulation of turgor pressure by linking solute import with wall loosening is discussed. Contents Summary 3 I. Introduction 4 II. Factors controlling cell expansion 4 III. Wall extensibility and yield threshold in roots 6 IV. Environmental effects on root cell expansion 10 V. Modification of cell wall biochemistry 15 VI. Linkage of growth with solute import 18 VII. Future prospects 21 VIII. Acknowledgements 22 IX. References 22.

Nitrate Supply and the Biophysics of Leaf Growth inSalix viminalis

The influence of nitrogen on leaf area development and the biophysics of leaf growth was studied using clonal plants of the shrub willow, Salix viminalis grown with either optimal (High N) or sub-optimal (Low N) supplies of nitrate. Leaf growth rate and final leaf size were reduced in the sub-optimal treatment and the data suggest that in young rapidly growing leaves, this was primarily due to changes in cell wall properties, since cell wall extensibility (% plasticity) was reduced in the Low N plants. The biophysical regulation of leaf cell expansion also differed with nitrogen treatment as leaves aged. In the High N leaves, leaf cell turgor pressure (P) increased with age whilst in the Low N leaves P declined with age, again suggesting that for young leaves, cell wall plasticity limited expansion in the Low N plants. Measurements of cell wall properties showed that cell wall elasticity (%E) was not influenced by nitrogen treatment and remained constant regardless of leaf age.

Photoinhibition of stem elongation by blue and red light: effects on hydraulic and cell wall properties.

The underlying mechanism of photoinhibition of stem elongation by blue (BL) and red light (RL) was studied in etiolated seedlings of pea (Pisum sativum L. cv Alaska). Brief BL irradiations resulted in fast transient inhibition of elongation, while a delayed (lag approximately 60 minutes) but prolonged inhibition was observed after brief RL. Possible changes in the hydraulic and wall properties of the growing cells during photoinhibition were examined. Cell sap osmotic pressure was unaffected by BL and RL, but both irradiations increased turgor pressure by approximately 0.05 megapascal (pressure-probe technique). Cell wall yielding was analyzed by in vivo stress relaxation (pressure-block technique). BL and RL reduced the initial rate of relaxation by 38 and 54%, while the final amount of relaxation was decreased by 48 and 10%, respectively. These results indicate that RL inhibits elongation mainly by lowering the wall yield coefficient, while most of the inhibitory effect of BL was due to an increase of the yield threshold. Mechanical extensibility of cell walls (Instron technique) was decreased by BL and RL, mainly due to a reduction in the plastic component of extensibility. Thus, photoinhibitions of elongation by both BL and RL are achieved through changes in cell wall properties, and are not due to effects on the hydraulic properties of the cell.

Monoclonal antibodies as tools in studying the differentiation of the dental mesenchyme: [formula omitted] Institute of Dentistry and Departments of Pathology and Immunology, University of Helsinki, SF-00280 Helsinki, Finland

Growth and development of etiolated pea (Pisum sativum L. cv. Alaska) and maize (Zea mays L. cv. Golden Cross Bantam) seedlings grown under simulated microgravity conditions were intensively studied using a 3-dimensional clinostat as a simulator of weightlessness. Epicotyls of etiolated pea seedlings grown on the clinostat were the most oriented toward the direction far from cotyledons. Mesocotyls of etiolated maize seedlings grew at random and coleoptiles curved slightly during clinostat rotation. Clinostat rotation promoted the emergence of the 3rd internodes in etiolated pea seedlings, while it significantly inhibited the growth of the 1st internodes. In maize seedlings, the growth of coleoptiles was little affected by clinostat rotation, but that of mesocotyls was suppressed, and therefore, the emergence of the leaf out of coleoptile was promoted. Clinostat rotation reduced the osmotic concentration in the 1st internodes of pea seedlings, although it has little effect on the 2nd and the 3rd internodes. Clinostat rotation also reduced the osmotic concentrations in both coleoptiles and mesocotyls of maize seedlings. Cell-wall extensibilities of the 1st and the 3rd internodes of pea seedlings grown on the clinostat were significantly lower and higher as compared with those on 1 g conditions, respectively. Cell-wall extensibility of mesocotyls in seedlings grown on the clinostat also decreased. Changes in cell wall properties seem to be well correlated to the growth of each organ in pea and maize seedlings. These results suggest that the growth and development of plants is controlled under gravity on earth, and that the growth responses of higher plants to microgravity conditions are regulated by both cell-wall mechanical properties and osmotic properties of stem cells.

The role of gibberellins in plant cell elongation

The gibberellins are an ubiquitous class of growth regulators in higher plants. They control various aspects of plant development and are known to be involved in all phases of the developmental cycle of angiosperms. These growth regulators were discovered because of the dramatic effect they exert on stem growth via effects on cell elongation. Gibberellins stimulate cell elongation by altering the rheological properties of the cell wall; as a consequence, the water potential of the cell is lowered allowing for water uptake and therefore an increase in cell volume. The precise mechanism for the change in cell wall properties brought about by the gibberellins is not known; however, we do know that the mechanism is not based on the secretion of protons as it is in the case of auxin‐stimulated growth.

Micromanipulation of stomatal guard cells

THE opening and closing of stomatal pores is controlled by deformations of the guard cells resulting from changes in the pressure relationships between epidermal and guard cells. Under natural conditions such changes are, in turn, controlled by changes in the osmotic concentrations of cell saps or by changes in cell water content, although they could also be controlled by changes in cell wall properties. We have measured the pressures required to bring about or maintain stomatal openings by applying pressures directly within subsidiary cells and guard cells of Tradescantia virginiana and Vicia faba leaves.

Radiation-induced stimulation of pollen-tube elongation in douglas-fir

Livingston G.K. and Stettler R.F. Radiation-induced stimulation of pollen-tube elongation in Douglas-fir. Radiation Botany 13, 65–72, 1973.-Mature pollen of Douglas-fir (Pseudotsuga menziesii) was subjected to gamma radiation from a 60 Co source at exposures of 4, 8, 16, 32, 64, 128 and 256 kR and incubated on an agar medium in vitro . Whereas germination per cents remained constant regardless of treatment, pollen-tube lengths at 48 hr of incubation were positively correlated with radiation dose. The same results were found with X rays. Irradiation seemed to both speed up germination and increase the rate of elongation. Oxygen uptake, as measured by a respirometer, increased proportionately to dose up to 64 kR but declined at higher doses. At the microscopic level, the two highest doses caused an exfoliation of the outer layers of the inline at the time of germination. It is suggested that the observed stimulation of pollen-tube elongation is brought about by an enhanced metabolism at the lower doses; but by a physical change in cell-wall properties at the higher doses.

Control of Auxin‐induced Stem Elongathn by the Epidermis

AbstractSegments of the 4th and 5th internodes of light‐grown pea seedlings were used for the study of control of stem elongation. With 5th internodes, at low turgor as well as at water saturation auxin primarily appeared to cause a change in cell wall properties of the epidermis but it showed little effect on expansion af the inner tissue. This was confirmed by comparison of expansion between peeled and unpeeled segments, split tests and by measurements of stress‐relaxation properties of the epidermal cell wall. Segments with the central part re‐moved elongated well in response to auxin, but the isolated epidermis showed neither auxin‐induced elongation nor cell wall loosening. A fungal β‐1,3‐glucanase appeared, at least partly, to have a similar effect as that of auxin on elongation, by changing cell wall properties of the epidermal cell wall. Peeled segments of 4th internodes expanded very little and auxin had little effect on their epidermal cell wall properties.

Stress-relaxation properties of plant cell walls with special reference to auxin action

Stress-relaxation analysis was employed to determine changes in cell wall properties of Avena coleoptile and green pea stem. The stress-relaxation curve of the cell wall was simulated by a model consisting of four Maxwell viscoelastic components. Auxin changes only the initial part of the curve, indicating that auxin primarily decreases the relaxation time of the model. Significance of the τ spectrum, representing a generalized Maxwell model for cell wall properties, is also discussed in terms of auxin action.