Coleoptile Cell Walls Research Articles

Cell Wall Bound Ferulic Acid in Barley Seedlings during Development and its Photoisomerization

Only the E-isomer of ferulic acid was detected in alkaline hydrolyzates of cell walls of coleoptiles and primary leaves of etiolated barley seedlings. The levels of E-ferulic acid increased significantly with growth reaching a maximum of 50 μ moles/g dry cell wall. The accumulation started one day later and finished one day later than the increase in dry weight of cell walls. On irradiation of dark grown plants the Z-isomer was produced in cell walls by direct photoisomerization of the E-isomer. The levels of Z-isomer formed did not change during a subsequent 21 hr dark incubation.

The Instron technique as a measure of immediate-past wall extensibility

The relationship between the plastic-extensibility values (PEx) obtained in the Instron technique and the growth parameter, wall extensibility (Φ) has been evaluated for Avena sativa L. coleoptile cell walls. The possibility that PEx is proportional to the growth rate rather than to Φ has been eliminated by showing that turgor-driven changes in the growth rate do not cause comparable changes in PEx. For Avena coleoptiles, PEx appears to be a measure of the average Φ over the previous 60-90 min rather than a measure of the instantaneous Φ of the growth equation. This is indicated by the fact that while PEx and the growth rate start to change simultaneously after addition of indole-3-acetic acid or KCN, the growth rate reaches a new, constant value 60-90 min before a new plateau value of PEx is obtained. Similar results are obrained with soybean (Glycine max L.) hypocotyl walls, indicating that the relationship between PEx and the parameter Φ is a general one, although the period over which Φ is averaged differs from tissue to tissue. In addition, it is shown that PEx can be measured more than once on the same section; a new potential for plastic extension is regenerated whenever the force vectors are changed even slightly. It is concluded that PEx is a measure of those domains in the wall where a wall-loosening event has occurred which has not been eliminated by further wall synthesis or other biochemical events.

Fusicoccin-Induced Acidification in the Cell Wall of Corn Coleoptiles Measured Electrophysiologically

Summary Fusicoccin (FC) induces changes of concentration potential and tissue resistance of corn coleoptiles within a few seconds after application. These changes are interpreted as a result of a rapid cell wall acidification caused by the plasmalemma proton pump stimulated by FC. Coleoptiles treated with indoleacetic acid (IAA) or light did not show any responses. A rough calculation of the amount of excreted protons is presented.

Autolytic activities of the cell wall in rice coleoptiles. Effects of nojirimycin

Oryza sativa L. var. bahia coleoptile cell walls show sufficient autolytic activity for the release into the surrounding medium of amounts up to 60 μg of sugars per mg of dry weight of cell wall. The products released elute in Bio‐gel P.2 as mono‐ and polysaccharides with glucose as the sole component. The polysaccharide component releases tri‐ and tetrasaccharides on treatment with a glucanase specific for β (1–3) (1–4) linkages in the same proportion as that of the mixed glucan of the cell wall. This supports the hypothesis that the polysaccharide component originates from the cell wall glucan and that autolysis is therefore related to the processes of the loss of rigidity of the cell wall. Nojirimycin (a specific glucanase inhibitor and inhibitor of auxin‐induced elongation) decreases autolytic activity of the cell walls, reducing it to 30% of its normal value. Bio‐gel P. 2 elution of the products released in autolysis in the presence of nojirimycin shows that only the monosaccharide fraction was affected.

Growth and cell wall changes in rice coleoptiles

A fractionation of non-cellulosic sugars of Oryza sativa L. coleoptile cell walls was carried out and the composition of each fraction was studied during coleoptile growth.Percentages of fractions extracted with boiling water and with oxalate (pectic substances) were almost constant throughout development. An increase in the K II hemicellulosic fraction (extracted with 24% KOH) content, and a decrease in the K I hemicellulosic fraction (extracted with 10% KOH) were detected, when coleoptile growth finished.The percentage of glucose content in the K I hemicellulosic fraction was highest in young coleoptiles and lowest in old ones. Furthermore, a highly significant linear relationship between amounts of glucose and growth rate was obtained, while a inverse relationship between the amount of xylose and arabinose and growth rate was attained.

Ion exchange properties of the corn coleoptile cell wall space. I. Concentration potentials and fixed charge activity

The measurements of the concentration potentials were used to calculate the negative fixed charge activity of the cell wall space of corn coleoptiles on the basis of a Donnan model. The results show a strong dependence of the fixed charge activity on the concentration of the external solutions. This is attributed to the dissociation of the carboxylic groups in the cell wall space characterized by a pK value of about 3.5.

Auxin-induced changes in the molecular weight of hemicellulosic polysaccharides of the Avena coleoptile cell wall

The average molecular weight of the water soluble hemicelluloses (hemicellulose B) of the Avena coleoptile cell wall was determined by gel permeation chromatography (GPC) and viscometry. Analysis of the neutral sugar composition of henucellulose B eluted from a GPC column (Sepharose 4B) indicated that it consists of β-glucan with a high molecular weight and arabinoxylan with a low molecular weight. A kinetic study of the effect of auxin on the molecular distribution of henucellulose B demonstrated that auxin decreased the β-glucan content of the hemicellulose as early as the first hour incubation, but not the arabinoxylan content, when it stimulated the extension of the coleoptile segments. Calculation of the weight-average molecular weight from the chromatograms suggested that auxin decreased the molecular weight of hemicellulose B; this was also confirmed by viscometry. Thus, auxin may cause cell wall loosening, leading to cell extension, through its effect on β-glucan degradation or through the decrease in the molecular weight of hemicellulose B.

Effect of cycloheximide and cordycepin on auxin-induced elongation and β-glucan degradation of noncellulosic polysaccharides of <italic>Avena</italic> coleoptile cell wall

Effect of cycloheximide and cordycepin on auxin-induced elongation and β-glucan degradation of noncellulosic polysaccharides of <italic>Avena</italic> coleoptile cell wall

Effect of auxin on changes in the oriented structure of wall polysaccharides in response to mechanical extension in oat coleoptile cell walls

Effect of auxin on changes in the oriented structure of wall polysaccharides in response to mechanical extension in oat coleoptile cell walls

Auxin-indnced changes in barley coleoptile cell wall composition

Auxin-indnced changes in barley coleoptile cell wall composition

CELL WALL STRUCTURE AND ELONGATION GROWTH IN ZEA MAYS COLEOPTILE TISSUE

SUMMARYData from pulse‐chase studies on the turnover of glycosidic linkages in cell walls of maize coleoptile sections and other work on the effect of auxin or low pH on sugar release from ‘sheets’ of cells derived from the same tissue are presented. The qualitative and quantitative effects of auxin and low pH on sugar release from cell sheets are almost identical in the short term. Using a recently derived model of the maize coleoptile cell wall, a hypothesis is proposed concerning the role of auxin‐induced proton release in the cleavage of glycosidic linkages in relation to growth.

Infrared analysis of oat coleoptile cell walls and oriented structure of matrix polysaccharides in the walls

Infrared absorption spectra of film specimens of oat coleoptile cell walls, before and after protease treatment and after treatment for removal of lipid materials, pectic substances and hemicellulose, were recorded, and the characteristic bands in the spectrum of the wall assigned. Polarization spectrum measurements on the wall provided evidence indicating that the non-cellulosic polysaccharide matrix as well as cellulose micronbrils has an oriented structure in the wall and that the oriented structure changes during extension growth as well as upon mechanical extension of the walls.

Structure of hemicellulosic polysaccharides of Avena sativa coleoptile cell walls

The glycosidic linkage compositions of intact and, in some cases, enzyme-degraded polysaccharides extracted from the cell walls of oat coleoptiles and subsequently purified have been examined. A major component is shown to be a glucuronoarabinoxylan similar in structure to those described for a variety of other monocots. The noncellulosic glucan component is a β-linked polymer containing both 1,4- and 1,3-linked glucosyl residues in a ratio of 2 to 1. Analysis of the oligosaccharide produced by ‘lichenase’ digestion of this β-glucan suggests that the the 1,3- and 1,4-glucosyl linkages repeat in regular fashion. A small amount of xyloglucan polysaccharides like those described for cell walls of dicots was also detected.

Matrix polysaccharides of oat coleoptile cell walls

Separation of component polysaccharides in extractable fractions of the noncellulosic matrix of Avena sativa coleoptile cell walls shows that the principal classes of polymers present are glucuronoarabinoxylans (GAX) and iodine-negative hemicellulosic β-glucans. Rhamnogalacturonan is a minor component. GAX contains about 5–10% glucuronic acid and its 4- O-methyl ether, arabinose in amount almost equal to xylose, and a small amount of galactose; some subfractions contained appreciable amounts of glucose and galacturonic acid but these may derive from separate, contaminating polysaccharides. From the sedimentation and diffusion coefficients and intrinsic viscosities of one subfraction each of the GAX and of the hemicellulosic glucan that had been purified to apparent homogeneity by criteria of sedimentation and borate electrophoresis, MWs of about 200 000 were calculated by two methods. The viscosity characteristics and gel-forming ability of the hemicellulosic glucan give evidence of appreciable molecular interactions which suggest that this polymer is an important structural component of the cell wall.

Effect of α-Tomatine on the Response of Wheat Coleoptile Segments to Exogenous Indole-3-acetic Acid

A concentration of 10−5 M tomatine had no effect on leakage from, or elongation of, wheat coleoptile segments, but consistently reduced IAA-enhanced extension growth by c. 50 per cent. There was no evidence of chemical interaction between the alkaloid and the auxin in solution, and IAA action was not affected by pre-treatment for up to 3 h with 10−5 M tomatine. Studies with [2-14C]IAA revealed that 10−5 M tomatine did not inhibit uptake of auxin into segments. The effect of pre-treating segments for up to 3 h with IAA could be virtually nullified by 10−5 M tomatine, as could also IAA-induced changes in properties of coleoptile cell walls. Results are discussed in relation to the ability of tomatine to disrupt membrane function and to current hypotheses implicating membranes in the primary action of auxin.

Phenolic Acids in Wheat Coleoptile Cell Walls

The phenolic constituent of nonvascular cell walls of wheat (Triticum aestivum L.) coleoptiles, which yields vanillin upon nitrobenzene oxidation, is not lignin as I previously claimed. It seems to be mainly ferulic acid bonded to carbohydrate, probably by an ester linkage. The acid is associated with a fraction of the wall rich in arabinose and xylose, although it is not known whether it is esterified directly with these pentose residues. The phenolic-carbohydrate complex is released by cellulase, but not by pronase or a mixture of hemicellulases.

Activation of Avena Coleoptile Cell Wall Glycosidases by Hydrogen Ions and Auxin

Several cell wall-bound glycosidases present in Avena sativa coleoptiles were assayed by following the hydrolysis of p-nitrophenyl-glycosides. Particular emphasis was placed on characterizing some parameters affecting the activity of beta-galactosidase. The pH optimum of this enzyme is 4.5 to 5.5; it is sensitive to copper ions and p-chloromercuribenzoate treatment and apparently has an exceptionally low turnover rate. Indoleacetic acid treatment enhanced in vivo beta-galactosidase activity of coleoptile segments by 36% over control after 60 minutes. This enhancement was prevented by abscisic acid and cycloheximide. High buffer strengths and low pH reduced the indoleacetic acid-enhanced increase in enzyme activity. These data lend support to the following proposed model of indoleacetic acid action. Indoleacetic acid enhances the release of hydrogen ions into the cell wall which promote the activities of cell wall glycosidases, some of which may participate in the cell extension process.

Auxin-induced Changes in Avena Coleoptile Cell Wall Composition

Sugar and uronic acid residues were derived from wall polysaccharides of oat (Avena sativa, var. Victory) coleoptiles by means of 2 N trifluoroacetic acid, 72% sulfuric acid, or enzymic hydrolysis. The products of hydrolysis were reduced and acetylated to form alditol acetates which were analyzed using gas chromatography. Time-course studies of auxin-promoted changes in various wall fractions indicate that when exogenous glucose was available, increases in certain wall constituents paralleled increases in length. However, under conditions where exogenous glucose was not available, and where wall synthesis was limited, such correlations with growth were not apparent. Under these latter conditions total wall weight initially increased slightly, then decreased. These changes in weight were the net of increases in cellulose and some noncellulosic constituents and a decrease of over 75% in noncellulosic glucose. When coleoptile sections were preincubated without exogenous glucose for 8 hours to deplete endogenous wall precursors and subsequently treated with auxin, there were no detectable increases in wall weight. There was instead an auxin-promoted decrease in wall weight, and this decrease paralleled a decrease in noncellulosic glucose. There were no significant changes in other wall components. The auxin-promoted decreases in noncellulosic glucose are interpreted as a possible step in the mechanism of growth.

Stress‐relaxation Properties of the Avena Coleoptile Cell Wall

AbstractChanges in the cell wall properties of Avena coleoptile segments were studied under various conditions by stress‐relaxation analysis. Rheological models consisting of four or an infinite number of Maxwell viscoelastic components were used. The stress‐relaxation parameters of these models, t1, to, T, Gi and stress/strain ratio, were determined. The following results were obtained.1. The 1/T1 increased and stress/strain ratio decreased with the age of the coleoptiles. Decapitation caused a decrease in l/t1.2. Auxin increased I/T1 but decreased to and stress/strain ratio within 5 minutes after application.3. Treatment with a fungal β‐l,3‐glucanase increased 1/T1 both in living and methanol‐killed, pronase‐treated coleoptiles. Cellulase did not cause the changes observed in the parameters of the isolated cell wall of the coleoptile segments. This held true for all treatments (with and without auxin, killed and pronase‐treated).The results obtained suggest that auxin primarily causes a partial degradation of the non‐cellulosic physaccharide components of the cell wall.

The Effect of Auxin on Stress Relaxation in Isolated Avena Coleoptiles

In order to characterize further the mechanical properties of coleoptile cell walls, stress relaxation measurements were made on methanol-boiled sections of Avena coleoptiles. Relaxation was measured both in mechanically conditioned specimens and in specimens which had not been previously extended. In both cases the relaxation was proportional to log time. Mechanical conditioning increased the relaxation modules and decreased the relative rate of relaxation. In contrast, pretreatment of the live coleoptiles with indoleacetic acid reduced the relaxation modulus and the absolute rate of relaxation but did not affect the relative rate of relaxation. Essentially similar pictures of the mechanical properties of coleoptile walls are obtained from stress relaxation and creep tests; the wall behaves as a nonlinear viscoelastic material.