Elongation Of Segments Research Articles

The regulation of nerve fiber length by intercalated elongation and retraction

Cell body movements were observed in cultures of rat sympathetic neurons that were accommodated by the elongation of neurite segments intercalated between the cell bodies and distal neurites. The elongation may represent growth of the neurites in response to mechanical tension arising from the cell body movements. Preliminary observations also suggest that neurites made slack may actively shorten. Control of nerve fiber length by mechanical tension could allow the nervous system to readily accommodate changes in the size and shape of the organism that occur during development and growth. It is possible that nerve growth factor promotes nerve fiber elongation indirectly through tension generated by growth cone movements.

Evidence against the acid-growth theory of auxin action

Four experimental predictions of the 'acid-growth theory' of auxin (indole-3-acetic acid, IAA) action in inducing cell elongation were reinvestigated using abraded segments of maize (Zea mays L.) coleoptiles. i) Quantitative comparison of segment elongation and medium-acidification kinetics measured in the same sample of tissue reveals that these IAA-induced processes are neither correlated in time nor responding coordinately to cations present in the medium. ii) Exogenous protons are not able to substitute for IAA in causing segment elongation at the predicted pH of 4.5-5.0. Instead, external buffers induce significant segment elongation only below pH 4.5, reaching a maximal response at pH 1.75-2.5. Acid and IAA coact additively, and therefore independently, in the whole range of feasible pH values. iii) Neutral or alkaline buffers (pH 6-10) are unable to abolish the IAA-mediated growth response and have no effect on its lag-phase. iv) Fusicoccin, at a concentration producing the same H(+) excretion as high concentrations of IAA, is ineffective in inducing segment elongation. Moreover, sucrose and other sugars can quantiatively substritute for IAA in inducing H(+) excretion but are likewise ineffective in inducing elongation. It is concluded that these results are incompatible with the acid-growth theory of auxin action.

Evidence for the acid-growth theory of fusicoccin action

Three predictions of the acid-growth theory of fusicoccin (FC) action in inducing cell elongation were reinvestigated using abraded segments of maize (Zea mays L.) coleoptiles. i) Quantitative comparison of segment elongation and medium-acidification kinetics measured in the same sample of tissue shows that these FC-induced processes are strictly correlated in time and respond coordinately to cations present in the medium. ii) Fusicoccin (1 μmol l(-1)) induces a rapid acidification of the cell-wall solution, reaching a final level of pH 3.8-4.0. Exogenous protons are able to substitute quantitatively for FC in causing segment elongation at pH 3.8-4.0. At pH 4, FC has no additional effect on cell elongation. iii) Neutral buffers (pH 7) completely abolish the FC-mediated growth response. iv) Cycloheximide (10 mg l(-1)) inhibits both FC-induced and acid-buffer(pH 4)-induced elongation after a lag of 40-45 min, and FC-induced H(+) excretion after a lag of 2 h. Under the same conditions, indole-3-acetic acid-induced elongation and H(+) excretion are inhibited without detectable lag. It is concluded that these results are fully compatible with the acid-growth theory of FC action.

Use of a pH-response curve for growth to predict apparent wall pH in elongating segments of maize coleoptiles and sunflower hypocotyls

To determine the relationship between apparent pH of the wall solution and shoot segment elongation, curves for the initial growth rates as a function of pH of the external solution were determined for maize (Zea mays L.) coleoptiles and sunflower (Helianthus annuus L.) hypocotyls and used to predict apparent wall pH in segments responding to indole-3-acetic acid (IAA) and fusicoccin (FC). When a solution having a pH predicted for walls of coleoptile segments responding to IAA was applied to the segments in the presence of IAA, this pH was not maintained. However, when the same was done for coleoptile segments responding to FC, the predicted pH was maintained in the external solution. Sunflower hypocotyl tissue did not maintain the external pH at the predicted value in the presence of either IAA or FC. The results indicate that wall loosening in coleoptiles caused by IAA may not be solely controlled by pH in the wall, yet growth (wall loosening) caused by FC apparently is directly related to wall pH. In sunflower the growth response to neither IAA nor FC appears to be directly correlated with wall pH.

Galactose inhibition of auxin‐induced cell elongation in oat coleoptile segments

Auxin‐induced cell elongation in oat coleoptile segments was inhibited by galactose; removal of galactose restored growth. Galactose did not appear to affect the following factors which modify cell elongation: auxin uptake, auxin metabolism, osmotic concentration of cell sap, uptake of tritium‐labeled water, auxin‐induced wall loosening as measured by a decrease in the minimum stress‐relaxation time and auxininduced glucan degradation. Galactose markedly prevented incorporation of [14C]‐glucose into cellulosic and non‐cellulosic fractions of the cell wall. It was concluded that galactose inhibited auxin‐induced long‐term elongation of oat coleoptile segments by interfering with cell wall synthesis.

Inhibition of 2,4-Dichlorophenoxyacetic Acid-Stimulated Elongation of Pea Stem Segments by a Xyloglucan Oligosaccharide

Xyloglucan, isolated from the soluble extracellular polysaccharides of suspension-cultured sycamore (Acer pseudoplatanus) cells, was digested with an endo-beta-1,4-glucanase purified from the culture fluid of Trichoderma viride. A nonasaccharide-rich Bio-Gel P-2 fraction of this digest inhibited 2,4-dichlorophenoxyacetic-acid-stimulated elongation of etiolated pea stem segments. The inhibitory activity of this oligosaccharide fraction exhibited a well-defined concentration optimum between 10(-2) and 10(-1) micrograms per milliliter. Another fraction of the same xyloglucan digest, rich in a structurally related heptasaccharide, did not, at similar concentrations, significantly inhibit the elongation.

Regulating Effects of Brassino Steroids and of Sterols on Growth and H+ Secretion in Maize Roots

Summary The effects of brassinosteroid, of twelve related sterols and of three sterols on maize root growth and on H+ secretion were investigated. A number of steroids stimulated root segment elongation and H+ secretion as brassinosteroid does. Defined structural requirements were found for the effect on growth; on the contrary, all the steroids tested, among which stigmasterol, cholesterol and ergosterol, were active on H+ secretion. Cholesterol stimulated K+ uptake and dark CO2 fixation, two processes generally associated with the activity of the H+ pump.

Oleic acid metabolism: A biochemical marker for studying photoregulation of epicotyl elongation in Vigna unguiculata

Oleic acid metabolism can be considered to be an indicator of growth photoregulation in cowpea (Vigna unguiculata Westphal cv. M53) epicotyls. Phosphatidylcholine and phosphatidylethanolamine are the two lipid classes concerned in the photoregulation of oleic acid accumulation. The incorporation of radioactive precursors in internodes of whole plants has shown that there is de novo synthesis of these phospholipids during the light dependent growth process.The variations in oleic acid content were used to study the photocontrol of elongation in segments excised from the apical part of the epicotyl. In this system, as in whole plants, oleic acid was the only fatty acid showing significant variation related to the light/dark treatments. Differences in photoresponse between excised intenode segments and internodes in whole plants are discussed.

Role of IAA conjugates in inducing ethylene production by tobacco leaf discs

Indole-3-acetic acid (IAA) labeled in its carboxyl group was metabolized by tobacco leaf discs (Nicotiana tabacum L. cv. Xanthi) into three metabolites, two of which were preliminarily characterized as a peptide and an ester-conjugated IAA. Reapplication of each of the three metabolites (at 10 μM) resulted in a marked stimulation of ethylene production and decarboxylation by the leaf discs. Similarly, these three IAA metab olites could induce elongation of wheat coleoptile segments, which was accompanied by decarboxylation. Both the exogenously supplied esteric and peptidic IAA conjugates were converted by the leaf discs into the same metabolites as free IAA. (1-14C)IAA, applied to an isolated epidermis tissue, was completely metabolized to the esteric and peptidic IAA conjugates. This epidermis tissue showed much higher ethylene production rates and lower decarboxylation rates than did the whole leaf disc. The results suggest that the participation of IAA conjugates in the regulation of various physiological processes depends on the release of free IAA, which is obtained by enzymatic hydrolysis of the conjugates in the tissue. The present study demonstrates biological activity of endogenous IAA conjugates that were synthesized by tobacco leaf discs in response to exogenously supplied IAA.

Invertase and auxin-induced elongation in internodal segments of Phaseolus vulgaris

A close positive correlation was observed between segment elongation and the specific activity of soluble acid invertase in stem segments of P. vulgaris incubated for 21 hr in the presence of IAA or of several synthetic auxins and auxin analogues. Optimum concentrations for the stimulation of growth and invertase activity were similar and varied from 10 −6 M (2,4-D) through 10 −5 M (IAA, IBA, α-NAA, β-NAA) to greater than 10 −4 (IPA, PoAA, trans-cinnamic acid). The weak activity of trans-cinnamic acid, a competitive inhibitor of auxin action, may have resulted from cis-trans isomerization during incubation. The concentration of hexose sugars in the segments fell during incubation in the presence of auxin, the greatest decline in hexose concentration occurring in the presence of compounds exhibiting the greatest stimulation of growth.

Effect of abscisic acid on growth and indolyl-3-acetic acid levels in maize roots

The abscisic acid (ABA) effect on root elongation is first reported comparing intact roots and apical root segments (prepared from primary roots of LG11 maize) treated 1 h by buffered (pH 6.0) ABA then kept 5 h in the dark (humid air or in buffered medium). After 1 h, ABA has no effect except at 10 −4 M for which it caused a small growth inhibition. After 6 h, ABA at 10 −8 M (1 h treatment) enhances the elongation of root segments. But, for 10 −6 M and 10 −4 M it inhibits growth of both intact roots and root segments. In a second set of analyses, endogenous indolyl-3-acetic acid (IAA) of these ABA treated roots is measured. When they were immersed, their auxin content — analysed by gas chromatography-mass spectrometry (GC-MS) — was lower in comparison to roots maintained in humid air. Such decrease in the IAA level was significantly enhanced in ABA treated roots. After 1 h incubation some IAA is detected in the incubation solution containing maize roots. Its concentration increases when intact roots immersed in that solution were incubated in the presence of ABA.

Tissue interactions in indoleacetic acid-induced rapid elongation of lupin hypocotyls

The role of individual tissues in the indoleacetic acid (IAA)-induced rapid elongation response of lupin hypocotyl segments was investigated. The effect on elongation of removing specific tissues from non-IAA-treated segments was first determined. The epidermis apparently limits elongation of intact segments, since a burst of extension occurred when it was removed by peeling. In peeled segments, the stele (vascular tissue and pith) apparently limits the rate of extension since its removal resulted in very rapid extension of the remaining cylinder of cortex. On IAA treatment, the response of segments with the stele removed was initially similar to that obtained with intact segments, suggesting that the epidermis and cortex only are involved in the initial response. In segments where the epidermis had previously been removed this initial response to IAA was absent, but there was a longer term response. These results suggest that the response of intact segments to IAA consists of two superimposed phases. The first is the result of epidermal ‘relaxation’ and the second is an independent elongation controlled by the cortex.

The significance of surface changes on explanted polyurethane pacemaker leads.

Although over 140,000 polyurethane leads have been implanted in humans, a controversy has recently arisen dealing with the significance of frequently detected irregularities on explanted insulator surfaces by scanning electron microscopy (SEM), and their relationship with lead failure. We therefore implanted ten, 6 Fr atrial polyurethane leads and an equal number of 4 Fr ventricular leads in dogs for a mean 26 +/- 2 and 29 +/- 2 weeks, respectively. Fourteen leads were removed utilizing metered force. The remaining leads were removed surgically without force at the termination of the study. Specimens were stored in saline prior to physical testing (tensile strength and elongation) of intravascular and extravascular lead segments. Similarly stored samples were prepared for SEM analysis. The polyurethane insulator disconnected from the electrode on forcible removal in three atrial and two ventricular leads (concordant connected from the electrode on forcible removal in three atrial and two ventricular leads (concordant for two pairs). There was no significant relationship between the results of physical testing and extraction force, lead size, integrity on removal, sample location or SEM scores. Chemical analysis of surface changes employing both x-ray and electron emission spectroscopy failed to reveal evidence of protein adsorption or liquid impregnation. Samples soaked in sodium hydroxide displayed the same SEM irregularities. The combined effects of fissuring and fluid absorption by polyurethane did not affect chronic anodal or cathodal thresholds. In conclusion, a clear relationship between chronic surface irregularities and the insulator function of polyurethane, its relationship between chronic surface irregularities and the insulator function of polyurethane, its integrity in situ, or its strength at explant has not been established by this relatively short-term study. On the other hand, a potential time-dependent impact of these changes on lead performance has not been excluded. Moreover, only a single species of medical grade polyurethane has been clinically evaluated. Thus, the ultimate place of polyurethane leads in pacing systems has yet to be determined.

Kinetics of indole acetic acid‐induced growth in hypocotyl sections of Vigna mdiata

The kinetics of auxin‐induced elongation of segments from Vigna radiata (L.) Wilczek hypocotyls have been investigated using auxanometer measurements. Doseresponse curves were established for several well‐defined parameters of the growth response. The experimental data revealed that different kinetic parameters were affected differently by increasing auxin concentrations. The dose‐response curves are slightly sigmoid for fresh weight, nearly bell‐shaped for total elongation or maximal elongation rate, and nearly linear for maximal growth acceleration. The effects of auxin concentration on regulation of growth orientation are discussed.A biphasic response is observed mainly with segments taken from the middle of the hypocotyl (‘C’) which exhibit maximal growth rates. Segments from other levels, with lesser growth potentials, exhibit a very weak response. The two successive phases may then require different maturation states. Kinetics of the acceleration curves are very similar all along the hypocotyl and remain very homogeneous with increasing IAA concentrations.

Stimulation of Maize Root Growth by Triazinone

Summary Triazinone (TA: 4-ethoxy-l-[ p -tolyl]- s -triazine-2,3 [1H, 3H]-dione) significantly increased the elongation of apical segments prepared from primary maize ( Zea mays cv. LG 11) roots. The growth-promoting effect of TA was stronger for the illuminated root segments than for those kept in the dark. In both conditions the optimal TA concentration was found to be about 4 × 10 -4 M. At that level for 48 h incubation TA enhanced root elongation of about 60% and 100% for root segments of respectively 5 and 10-20 mm in initial length.

Ethylene effects on growing and gravireacting maize root segments

The effects of ethylene pretreatments (500 nl/l for 1 h) and treatments (100 nl/1 to 1000 nl/l for 6 h) on elongation and gravireaction of apical maize root segments were tested in light and in the dark. Ethylene was found to affect weakly root elongation and gravireaction, but to induce strong curvatures for root growing vertically.

Evidence for Receptor Function of Auxin Binding Sites in Maize

When 3- to 4-day-old dark-grown maize (Zea mays L. WF9 x Bear 38) seedlings are given red light, auxin-binding activity localized on endoplasmic reticulum membranes of the mesocotyl begins to decrease after 4 hours; by 9 hours, it falls to 50 to 60% of that in dark controls, on either a fresh weight or total particulate protein basis. Endoplasmic reticulum-localized NADH:cytochrome c reductase activity decreases in parallel. Loss of binding is due to decrease in number of sites, with no change in their affinity for auxin (K(d) 0.2 micromolar for naphthalene-1-acetic acid). Elongation of mesocotyl segments in response to auxin decreases with a similar time course. Elongation of segments from irradiated plants shows the same apparent affinity for auxin as that of the dark controls. Auxin-binding activity and elongation response also decrease in parallel down the length of the mesocotyl. These observations are consistent with a role of endoplasmic reticulum-localized auxin binding sites as receptors for auxin action in cell elongation.

Inhibition of auxin‐induced cell elongation by galactose

Galactose at concentrations higher than 3 mM inhibited specifically auxin‐induced elongation of oat, wheat and rice coleoptile segments but not of pea and mung bean stem segments. Glucose, arabinose, rhamnose, xylose, mannose and glucosamine did not inhibit auxin‐induced elongation of coleoptile segments. Galactose inhibited auxin‐induced but not hydrogen ion‐induced growth.

Kinetic analysis of root growth and georeaction

The kinetics of growth and georeaction of horizontal or vertical maize (cv. ORLA 264) apical root segments were analysed. Elongation and curvature data were fitted to a mathematical function and the effect of both light and decapitation reported. Elongation of horizontal segments was found to be more sensitive to light than to decapitation. A light treatment or the decapitation presented several effects on the shape of the growth curves. Growth of vertical segments was affected much more by decapitation than by light treatment. The shape of the curves was clearly different for decapitated and intact segments.Curvature is affected both by light and decapitation but the shape of the bending curves is modified principally by decapitation.Under the present conditions used, growth and georeaction of root segments do not seem to be strictly correlated.

The role of the epidermis in auxin-induced and fusicoccin-induced elongation of Pisum sativum stem segments

The effects of peeling and wounding on the indole-3-acetic acid (IAA) and fusicoccin (FC) growth response of etiolated Pisum sativum L. cv. Alaska stem tissue were examined. Over a 5 h growth period, peeling was found to virtually eliminate the IAA response, but about 30% of the FC response remained. In contrast, unpeeled segments wounded with six vertical slits exhibited significant responses to both IAA and FC, indicating that peeling does not act by damaging the tissue. Microscopy showed that the epidermis was removed intact and that the underlying tissue was essentially undamaged. Neither the addition of 2% sucrose to the incubation medium nor the use of a range of IAA concentrations down to 10(-8) M restored IAA-induced growth in peeled segments, suggesting that lack of osmotic solutes and supra-optimal uptake of IAA were not important factors over this time period. It is concluded that, although the possibility remains that peeling merely allows leakage of hydrogen ions into the medium, it seems more likely that peeling off the epidermis removes the auxin responsive tissue.