Enhancement of Wall Loosening and Elongation by Acid Solutions
TL;DR: It is shown that the pH response can be clearly separated from the CO(2) response, and certain other aspects of the growth and wall-loosening responses, are described.
Abstract: The ability of low pH and CO(2) to induce rapid cell elongation and wall loosening in the Avena coleoptile has been examined with the use of a continuous growth-recording technique and an Instron extensometer, respectively. In particular, the properties of the response to hydrogen ions have been examined in detail and have been compared with the responses initiated by CO(2) and auxin. The optimal pH for growth is about 3.0, and both the maximal growth rate and wall extensibility are similar to that produced by optimal auxin. The timing (initiated in less than 1 minute) and duration (up to 2 hours) of the response to hydrogen ions, as well as certain other aspects of the growth and wall-loosening responses, are described. It is shown that the pH response can be clearly separated from the CO(2) response. Possible mechanisms for the initiation of the growth response to low pH are briefly discussed.
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TL;DR: Recent discoveries have uncovered how plant cells synthesize wall polysaccharides, assemble them into a strong fibrous network and regulate wall expansion during cell growth.
Abstract: Plant cells encase themselves within a complex polysaccharide wall, which constitutes the raw material that is used to manufacture textiles, paper, lumber, films, thickeners and other products. The plant cell wall is also the primary source of cellulose, the most abundant and useful biopolymer on the Earth. The cell wall not only strengthens the plant body, but also has key roles in plant growth, cell differentiation, intercellular communication, water movement and defence. Recent discoveries have uncovered how plant cells synthesize wall polysaccharides, assemble them into a strong fibrous network and regulate wall expansion during cell growth.
2,832 citations
Cites background from "Enhancement of Wall Loosening and E..."
...Expansin Growing plant cells characteristically exhibit ACID GROWTH...
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TL;DR: The Acid Growth Theory, which states that when exposed to auxin, susceptible cells excrete protons into the wall (apoplast) at an enhanced rate, resulting in a decrease in apoplastic pH, activates wall-loosening processes, the precise nature of which is unknown.
Abstract: Plant cells elongate irreversibly only when load-bearing bonds in the walls are cleaved. Auxin causes the elongation of stem and coleoptile cells by promoting wall loosening via cleavage of these bonds. This process may be coupled with the intercalation of new cell wall polymers. Because the primary site of auxin action appears to be the plasma membrane or some intracellular site, and wall loosening is extracellular, there must be communication between the protoplast and the wall. Some "wall-loosening factor" must be exported from auxin-impacted cells, which sets into motion the wall loosening events. About 20 years ago, it was suggested that the wall-loosening factor is hydrogen ions. This idea and subsequent supporting data gave rise to the Acid Growth Theory, which states that when exposed to auxin, susceptible cells excrete protons into the wall (apoplast) at an enhanced rate, resulting in a decrease in apoplastic pH. The lowered wall pH then activates wall-loosening processes, the precise nature of which is unknown. Because exogenous acid causes a transient (1-4 h) increase in growth rate, auxin must also mediate events in addition to wall acidification for growth to continue for an extended period of time. These events may include osmoregulation, cell wall synthesis, and maintenance of the capacity of walls to undergo acid-induced wall loosening. At present, we do not know if these phenomena are tightly coupled to wall acidification or if they are the products of multiple independent signal transduction pathways.
786 citations
01 Jan 1989
TL;DR: Transplasmalemma Redox Activity and the H+ -ATPase, as well as Evolutionary Relationships, are studied.
Abstract: INTRODUCTION . . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 PHYSIOLOGICAL ROLE OF THE PROTON PUMP . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 Suggested Functions... . . . . . . . .. . . . . . ... . . . . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . 62 Evidence from Studies with Yeast Mutants . . . . . . . . . . . . . . . . .... . . . . . . . ...... . . . 63 Relationship Between H+ -ATPase and K+ Transport . . . . . . . . . . . . . . ... . . .. . . . . . . . . . .. . . . . . 64 REGULATION OF PLASMA MEMBRANE ATPase ACTIVITy . . . . . . . . . . . . . . . . . . . . . . . . . 65 Factors Modulating ATPase activity . . . . . . . . . . . . . ..... . . . . ..... . . . . . . . . . . . ... . . . . . . . . .. . . . . . . . 65 Possible Regulation by Protein Kinases . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ... . . . . . . . . . . . . 66 Transplasmalemma Redox Activity and the H+ -ATPase . . . . . . .. . . . . . . . . . . . . . . . . . . . . .. . . . . 69 STRUCTURE AND MECHANISM OF (E-P) ATPases . . . . .. . . . . . . . .. . . . . . . . . . . . . . . . . . . . . . . . 69 Evolutionary Relationships . . . . ..... . . . . . . . .. . . .. . ... . . . . . .... . . . . . . . . . . . . . .. .. . . . . . . . . . . .. . . . . . 69 Alignment of ATPase Sequences Based on Structure Prediction . . . . ... . . ... . . . . . . . . . . . . 7 1 Functional Domains . .. . . .. . . . . ... . .. . . . .. . . . . . . . . . . . . . . . . .. . . . . ..... . . . . . .. . . . . . . . .. . . . . . . . . . . . . . 80 Coupling Mechanism . . . . . . . . . . . . . ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .... . . . . . . . . . . . . . . . . . . . . . . .... . . 86 SUMMARY AND PERSPECTIVES . . . . . . . . . . ..... . . . . . . . . . . . . . . . . . . . . . . .. . . . . . . . . . . . . . .. . . . . . . .. 88
585 citations
01 Jan 1999
TL;DR: A summary model for wall extension is presented, in which expansin is a primary agent of wall extension, whereas endoglucanases, xyloglucaan endotransglycosylase, and other enzymes that alter wall structure act secondarily to modulate expansin action.
Abstract: Polysaccharides and proteins are secreted to the inner surface of the growing cell wall, where they assemble into a network that is mechanically strong, yet remains extensible until the cells cease growth. This review focuses on the agents that directly or indirectly enhance the extensibility properties of growing walls. The properties of expansins, endoglucanases, and xyloglucan transglycosylases are reviewed and their postulated roles in modulating wall extensibility are evaluated. A summary model for wall extension is presented, in which expansin is a primary agent of wall extension, whereas endoglucanases, xyloglucan endotransglycosylase, and other enzymes that alter wall structure act secondarily to modulate expansin action.
553 citations
Cites background from "Enhancement of Wall Loosening and E..."
...This view is supported by the fact that sustained wall extension can indeed occur in vitro, without the direct need for wall synthesis (22, 94)....
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TL;DR: Recent progress on hormone biosynthesis and on hormonal transduction pathways has been impressive, but there are many blanks still to be filled in and the rate at which new discoveries are made will continue to accelerate.
Abstract: It is 60 years since Went and Thimann (1937) published their classic book Phytohormones. At that time, the term phytohormone was synonymous with auxin, although the existence of other phytohormones, such as cell division factors, was anticipated on the basis of physiological experiments. It is impressive that aside from some confusion about the structure of auxin, many of the basic phenomena of auxin physiology were already known at that time. It is equally impressive that much auxin biology, including the CholodnyWent hypothesis (Went and Thimann, 1937) regarding the role of auxin in mediating graviand phototropism, the pathway of auxin biosynthesis, and the mechanism by which auxin causes cell wall loosening, remains controversial. Since 1937, gibberellin (GA), ethylene, cytokinin, and abscisic acid (ABA) have joined auxin as phytohormones, and together, they are regarded as the "classical five" (Figure 1). This group is expected to grow as the hormonal functions of other compounds are recognized and as new hormones are discovered (see Creelman and Mullet, 1997, in this issue). As is evident from this short review, recent progress on hormone biosynthesis and on hormonal transduction pathways has been impressive. Also evident is that there are many blanks still to be filled in. With the application of the powerful new techniques of chemical analysis and molecular genetics, the rate at which new discoveries are made will continue to accelerate. It's a great time to be a plant hormonologist!
537 citations
Cites background from "Enhancement of Wall Loosening and E..."
...To promote growth, plant hormones are expected to cause loosening of the cell wall, but how is this achieved? The acid-growth theory postulates that secretion of hydrogen ions into the cell wall is stimulated by auxin and that the lowered pH in the apoplast activates wall-loosening processes (Rayle and Cleland, 1970; Hager et al., 1971)....
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References
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484 citations
TL;DR: Analysis of the data indicates that auxin probably does not act on the elongation of these tissues by promoting the synthesis of informational RNA or of enzymatic protein, and the speed with which cycloheximide inhibits elongation suggests that continual protein synthesis may be important in the mechanism of cell wall expansion.
Abstract: The timing of the auxin response was followed in oat and corn coleoptile tissue by a sensitive optical method in which the elongation of about a dozen coleoptile segments was recorded automatically. The response possesses a latent period of about 10 min at 23°C, which is extended by low concentrations of KCN or by reducing the temperature, but is not extended by pretreatments with actinomycin D, puromycin, or cycloheximide at concentrations that partially inhibit the elongation response. Analysis of the data indicates that auxin probably does not act on the elongation of these tissues by promoting the synthesis of informational RNA or of enzymatic protein. Not excluded is the possibility that auxin acts at the translational level to induce synthesis of a structural protein, such as cell wall protein or membrane protein. While the data do not provide direct support for this hypothesis, the speed with which cycloheximide inhibits elongation suggests that continual protein synthesis may be important in the mechanism of cell wall expansion.
173 citations
"Enhancement of Wall Loosening and E..." refers background or methods in this paper
...The elongation of coleoptiles was measured by the high resolution continuous recording technique of Evans and Ray (6)....
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...A comparison of the pH response with the growth responses initiated by CO2 (7) and auxin (6) suggests that the three processes are unique and different....
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TL;DR: It is concluded that the increase of growth rate in acid buffers is due to the conversion of growth substance already in the plant from an inactive salt form to an active non-dissociated form.
Abstract: 1.
The growth of theAvena coleoptile in buffer solutions of different pH has been investigated. The formation of curvatures in acid solutions by plants having the epidermis removed from one side has been confirmed.
2.
Acid solutions increase the growth rate by increasing the cell wall plasticity. Increase of cell wall plasticity is known to result from the action of growth substance.
3.
The increase of growth rate in acid buffers is inhibited by HCN concentrations of the same order as those which inhibit the increase of growth rate due to growth substance.
4.
There is no increase in cell-acidity under the influence of growth substance.
5.
There is growth substance present in the plant even after the hormone producing tip is removed.
6.
The increase of growth rate with decrease ofinternal pH follows closely the increase of non-dissociated acid with decrease of pH in a solution of the weak acid, growth substance.
7.
From the foregoing it is concluded that the increase of growth rate in acid buffers is due to the conversion of growth substance already in the plant from an inactive salt form to an active non-dissociated form.
93 citations
TL;DR: A reassessment of the turgor pressure of intact Avena coleoptiles has shown that it is greater than Pc, and it is proposed that wall extension involves two steps, each of which requires turgar pressure.
Abstract: 1.
Auxin-induced wall loosening, as measured by the Instron extensometer technique, and the conversion of wall loosening into extension, as measured by cell elongation, differ in their relationship to turgor pressure (TP). Wall loosening can occur at any TP greater than zero while rapid cell extension only occurs when the TP exceeds a critical value (Pc).
2.
The amount of auxin-induced increase in wall extensibility is proportional to the turgor pressure in the region between Pc and zero. In the absence of auxin, wall extensibility decreases slightly when TP exceeds Pc.
3.
A reassessment of the turgor pressure of intact Avena coleoptiles has shown that it is greater than Pc. The TP of intact Avena coleoptiles is sufficient to permit turgor-driven cell elongation to occur.
4.
It is proposed that wall extension involves two steps, each of which requires turgor pressure. Covalent bonds which render the wall rigid are broken only when the wall is under tension and when auxin is present in the tissue. Extension of the wall then requires that hydrogen bonding between polymers be broken by a TP in excess of Pc.
78 citations
TL;DR: It is shown that auxin increases the extensibility of Avena coleoptile sections and this increase occurs even when elongation is osmotically inhibited, which would indicate that RNA svnthesis is required for auxin action.
Abstract: Actinoiiiycini D, an inllibitor of RNA synthesis (10, 12), will prevent auxin-induced cell elongation (4. 8. 12, 16). It has been assumed that it acts by inhibiting the action of auxin (8, 12, 16). If this is correct, it would indicate that RNA svnthesis is required for auxin action. Auxin-induced elongation is a complex process which requires a number of factors (5). In Avena coleoptile tissues the factor which normally controls elongation is the extensibility of the cell wall (2, 7, 21). Addition of auxin to a tissue causes a loosening of the cell wall which, in turn, results in rapid elongation. Any inhibitor that blocks the auxin-induced wall loosening will inhibit elongation. But a compound that inhibits elongation does not necessarily have to have any effect on wall loosening. Mannitol, for example, inhibits rapid elongation but does not affect wall loosening (2). Since other auxin-insensitive factors are needed for growth, inhibition of any of these will also lead to an inhibition of elongation. Thus a compound could inhibit elongation either by blocking the auxin-induced wall loosening or by affecting some other factor. In the past, it has not been l)ossil)le to separate these 2 possibilities. Recently Olsen et al. (18) have shown that it is l)ossible to directly measure the extensibility of the wall by using a modification of the technique of Heyn (9). At the end of the incubation period, the bulk of the protoplasm is removed from the cells with boiling methanol followed by Pronase. Then an Instron stress-strain analyzer is used to measure the load which develops across the walls as the walls are subjected to a constant rate of strain. The strain per unit stress (WEx) is determined from the resulting load-extension curve. It should be noted that WEx is a measure of the combined elastic and plastic extensibility of the walls. Using this technique, Olson et al. (18) have shown that auxin increases the extensibility of Avena coleoptile sections. This increase occurs even when elongation is osmotically inhibited (17). This technique can be used to study the effects of inhibitors on auxin-induced wall extensibility. This investigation was undertaken in order to deter-
63 citations
"Enhancement of Wall Loosening and E..." refers methods in this paper
...Avena seedlings were grown as described earlier (2), and coleoptiles were used when they were 25 to 32 mm in length....
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