Mechanism of Gibberellin-Dependent Stem Elongation in Peas

Cosgrove, Daniel J.; Sovonick-Dunford, Susan

doi:10.1104/pp.89.1.184

Cited by 89 publications

(53 citation statements)

References 22 publications

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“…However, we found that GA3 caused a slight reduction in osmotic and turgor pressure of R-grown cucumber hypocotyls. This supports previous work with dwarf watermelon (26) and dark-grown peas (10). Likewise, Stuart and Jones (22) found poor correlation between osmotic pressure and GA3-induced changes in growth rate in lettuce seedlings.…”

Section: Discussionsupporting

confidence: 77%

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Gibberellic Acid Stimulation of Cucumber Hypocotyl Elongation

Taylor

Cosgrove²

1989

Plant Physiol.

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Recently developed techniques have been used to reinvestigate the mechanism by which gibberellic acid (GA3) stimulates elongation of light-grown cucumber (Cucumis sativus L.) seedlings. Osmotic pressure and turgor pressure were slightly reduced in GA3-treated seedlings, which elongated 3.5 times faster than control seedlings. This indicated that GA3 enhancement of growth was not controlled by changes in the osmotic properties of the tissues. Stress/strain (Instron) analysis revealed that plastic extension of the cell walls of GA3-treated seedlings increased by up to 35% above the control values. Stress-relaxation measurements on frozen-thawed tissue showed that To, the minimum relaxation time, was reduced following application of GA3. In vivo wall relaxation (measured by the pressure block technique)showed that the wall yield coefficient was increased, and the yield threshold was slightly reduced. Thus GA3 affected both the mechanical (viscoelastic) and biochemical (chemorheological) properties of the cell walls of light-grown cucumber. The previous hypothesis, that GA3 stimulates cucumber hypocotyl growth by increasing osmotic pressure and cell turgor, is contradicted by our results.GA3 can reverse the inhibition of stem elongation caused by light in many plant species (1,12,17,18,21,23,24). The mechanism by which GA3 enhances the rate of elongation has been investigated by several groups, many of whom have concluded that GA3 acts on cell wall mechanical properties to increase growth (2,13,15,18,20).Cucumber is an often-cited exception to this general trend, in that GA3 is thought to stimulate hypocotyl elongation by causing increases in cell turgor pressure and osmotic pressure. This hypothesis, however, is based on meager direct evidence. Rather, it is indirectly supported by studies which found little effect of GA3 on the mechanical properties of growing walls (5, 14), and it assumes that wall growth properties are well correlated with wall mechanical properties (4). This assumption, however, is sometimes invalid. For example, a recent study (8) Therefore, this study was undertaken to reexamine the mechanism by which GA stimulated elongation in lightgrown cucumber. Osmotic and turgor pressures were measured directly, and in vivo wall relaxation properties were assessed in living tissue using the pressure block technique. We also assessed wall mechanical properties in frozen-thawed tissue by stress-relaxation and Instron analyses. MATERIALS AND METHODS Plant Material

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Section: Discussionsupporting

confidence: 77%

“…A second order polynomial was used to fit the resulting curves, from which values for total, elastic and plastic extensibilities were obtained (10).…”

Section: Plant Materialsmentioning

confidence: 99%

Gibberellic Acid Stimulation of Cucumber Hypocotyl Elongation

Taylor

Cosgrove²

1989

Plant Physiol.

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“…2). These conclusions are consistent with current interpretation of physical parameters regulating cell enlargement in Pisum (6,7).…”

Section: Correlation Of Wall Plasticity With Sheath Expansionsupporting

confidence: 80%

“…Stuart and Jones (24) concluded that GA-induced increases in elongation were regulated by changes in wall extensibility, and that in the absence ofincreased extensibility, changes in turgor pressure had little direct effect. In another report (7), etiolated pea stems treated with an inhibitor of GA synthesis showed a significant threefold decline in relative growth rate that was reversed by addition of GA. Measurements on individual cortical cells showed that turgor pressure and yield threshold was greater for inhibitor-treated cells than for inhibitor + GA-treated cells but the differences were not large enough to explain the differences in intact growth. The authors attributed this to the effects of excision which was found to reduce growth rate also.…”

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confidence: 99%

Gibberellic Acid Regulates Cell Wall Extensibility in Wheat (Triticum aestivum L.)

Keyes¹,

Sorrells²,

Setter³

1990

Plant Physiol.

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Mutations (Rht genes) blocking sensitivity to gibberellic acid (GA) were used to examine phytohormone mediated cell wall expansion in wheat (Triticum aestivum L.). Irreversible extensibility of immature leaf segments, as determined by stress/strain (instron) measurements, declined with Rht gene dose. Exogenous GA3 significantly increased wall extensibility in the nonmutant controls but had no effect on the near-isogenic GA-insensitive genotypes. Furthermore, ancymidol, an inhibitor of gibberellin biosynthesis, diminished wall extensibility in the nonmutant control. Extensibility of immature segments was highly correlated with mature leaf sheath length (R = +0.95). The results indicate that wall yielding properties of expanding wheat leaves are associated with leaf cell expansion potential and that GA is involved in the determination of those properties.The plane of cell division together with the rate and orientation of irreversible expansion determine cell size and shape. The rate of plant cell expansion may be further reduced to a few physical components including: (a) cell wall extensibility, which is the capacity of the wall to undergo irreversible (plastic) extension in response to a load; (b) the yield threshold of the wall, which is the minimum stress required to initiate extension; (c) hydraulic conductance, the capacity ofthe tissue to transport water to the expanding cell; and (d) the difference in water potential between the cell and extracellular space (16). Lockhart's (16) equations show that a change in the growth rate can take place with changes in wall structural/ mechanical properties which determine extensibility and/or changes in hydraulic processes and/or turgor changes.Heyn (9)

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“…In peas, GA,-dependent growth is brought about by a similar biophysical mechanism (Cosgrove and Sovonick-Dunford, 1989), whereas R lowers the wall yield coefficient alone (Kigel and Cosgrove, 1991).…”

Section: --mentioning

confidence: 99%

Phytochrome, Gibberellins, and Hypocotyl Growth (A Study Using the Cucumber (Cucumis sativus L.) long hypocotyl Mutant)

et al. 1995

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The possible involvement of gibberellins (CAs) in the regulation of hypocotyl elongation by phytochrome was examined. Under white light the tal1 long hypocotyl (Ih) cucumber (Cucumis sativus L.) mutant, deficient in a type B-like phytochrome, shows an increased "responsiveness" (defined as response capability) to applied CA, (the main endogenous active CA) compared to the wild type. Supplementing far-red irradiation results in a similar increase in responsiveness in the wild type. Experiments involving application of the precursor GA, and of an inhibitor of CA, inactivation suggest that both the GA, activation and inactivation steps are phytochrome independent. Endogenous C A levels of whole seedlings were analyzed by combined gas chromatography-mass spectrometry using deuterated interna1 standards. The levels of GA, (and those of CA,,, the inactivated CA,) were lower in the //I mutant under low-irradiance fluorescent light compared with the wild type, similar to wild type under higher irradiance light during the initial hypocotyl extension phase, and higher during the phase of sustained growth, in which extension involved an increase in the number of cells in the upper region. In all cases, growth of the Ih mutant was more rapid than that of the wild type. It is proposed that CA, and phytochrome control cell elongation primarily through separate mechanisms that interact at a step close to the terminal response.

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Mechanism of Gibberellin-Dependent Stem Elongation in Peas

Cited by 89 publications

References 22 publications

Gibberellic Acid Stimulation of Cucumber Hypocotyl Elongation

Gibberellic Acid Stimulation of Cucumber Hypocotyl Elongation

Gibberellic Acid Regulates Cell Wall Extensibility in Wheat (Triticum aestivum L.)

Phytochrome, Gibberellins, and Hypocotyl Growth (A Study Using the Cucumber (Cucumis sativus L.) long hypocotyl Mutant)

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