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Ethylene and Auxin in the Control of Wood Formation
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

This thesis considers aspects of the regulation of growth rate and fibre properties in forest trees. These properties are both genetically determined and influenced by environmental stimuli. Induction of reaction wood is an environmentally induced process involving changes in growth rate and fibre properties that can be readily studied. Plant hormones are signalling agents that play important roles in the initiation and coordination of wood formation; in this thesis the plant hormones auxin and ethylene were investigated using gas chromatography/mass spectrometry (GC/MS). A novel MS technique for measuring the ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC) in minute amounts of plant tissue was developed. Ethylene is often connected to stress responses in plants, and ethylene evolution is increased when reaction wood is formed. Here it is demonstrated that this increase is regulated by ACC oxidase, the enzyme catalysing the last step in the ethylene biosynthetic pathway. This is in contrast to most of the earlier findings that tended to indicate that ethylene production directly reflects the availability of ACC. Although ethylene is strongly up-regulated during reaction wood formation, its role in modulating the growth rate and fibre properties remains unknown. Further, it is demonstrated that reaction wood in both poplar (Populus tremula L.) and pine (Pinus sylvestris L.) is formed without changes in auxin concentration in the cambial tissues. This suggests that the previously held assumption that the difference in auxin concentration is key factor in the induction of reaction wood is unsound. Further, auxin concentrations were compared in hybrid aspen trees (Populus tremula L. x tremuloides Michx.) growing vertically at different growth rates. These trees showed good correlations between auxin levels and growth rates. The growth rate was mediated by increases in the cell cycling rate rather than in the width of the cell division zone. Thus, the growth rate in poplar was correlated to auxin levels in normal wood formation, but not during reaction wood formation.

Place, publisher, year, edition, pages
Umeå: Swedish University of Agricultural Sciences , 2003. , 40 p.
, Acta Universitatis Agriculturae Sueciae Silvestria, ISSN 1401-6230 ; 268
Keyword [en]
auxin ; ethylene ; lignification ; growth rate ; fibres ; cambium ; gas chromatography ; reaction wood ; organic acids ; mass spectrometry ; populus tremula ; pinus sylvestris
National Category
Forest Science Natural Sciences Chemical Sciences
Research subject
URN: urn:nbn:se:umu:diva-79571ISBN: 91-576-6502-8OAI: diva2:642990
Public defence
2003-03-28, 10:00 (English)

Retroaktiv registrering.

Available from: 2013-08-30 Created: 2013-08-23 Last updated: 2013-08-30Bibliographically approved
List of papers
1. Asymmetric expression of a poplar ACC oxidase controls ethylene production during gravitational induction of tension wood
Open this publication in new window or tab >>Asymmetric expression of a poplar ACC oxidase controls ethylene production during gravitational induction of tension wood
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2003 (English)In: The Plant Journal, ISSN 0960-7412, E-ISSN 1365-313X, Vol. 34, no 3, 339-349 p.Article in journal (Refereed) Published
Abstract [en]

Ethylene is produced in wood-forming tissues, and when applied exogenously, it has been shown to cause profound effects on the pattern and rate of wood development. However, the molecular regulation of ethylene biosynthesis during wood formation is poorly understood. We have characterised an abundant 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase gene (PttACO1) in the wood-forming tissues of Populus tremula (L.) × P. tremuloides (Michx). PttACO1 is primarily expressed in developing secondary xylem, and is specifically upregulated during secondary wall formation. Nevertheless, according to GC–MS analysis combined with tangential cryosectioning, the distribution of ACC was found to be fairly uniform across the cambial-region tissues. Gravitational stimulation, which causes tension wood to form on the upper side of the stem, resulted in a strong induction of PttACO1 expression and ACC oxidase activity in the tension wood-forming tissues. The ACC levels increased in parallel to the PttACO1 expression. However, the increase on the upper (tension wood) side was only minor, whereas large amounts of both ACC and its hydrolysable conjugates accumulated on the lower (opposite) side of the stem. This suggests that the relatively low level of ACC on the tension wood side is a result of its conversion to ethylene by the highly upregulated PttACO1, and the concurrent accumulation of ACC on the opposite side of the wood is because of the low PttACO1 levels. We conclude that PttACO1 and ACC oxidase activity, but not ACC availability, are important in the control of the asymmetric ethylene production within the poplar stem when tension wood is induced by gravitational stimulation.

Place, publisher, year, edition, pages
Blackwell Publishing, 2003
ACC oxidase, development, ethylene, gravistimulation, tension wood, secondary xylem
National Category
urn:nbn:se:umu:diva-79573 (URN)10.1046/j.1365-313X.2003.01727.x (DOI)000182455200008 ()
Available from: 2013-08-23 Created: 2013-08-23 Last updated: 2014-02-14Bibliographically approved
2. Patterns of Auxin Distribution during Gravitational Induction of Reaction Wood in Poplar and Pine
Open this publication in new window or tab >>Patterns of Auxin Distribution during Gravitational Induction of Reaction Wood in Poplar and Pine
2004 (English)In: Plant Physiology, ISSN 0032-0889, E-ISSN 1532-2548, Vol. 135, no 1, 212-220 p.Article in journal (Refereed) Published
Abstract [en]

Gravistimulation of tree stems affects wood development by unilaterally inducing wood with modified properties, called reaction wood. Commonly, it also stimulates cambial growth on the reaction wood side. Numerous experiments involving applications of indole-3-acetic acid (IAA) or IAA-transport inhibitors have suggested that reaction wood is induced by a redistribution of IAA around the stem. However, in planta proof for this model is lacking. Therefore, we have mapped endogenous IAA distribution across the cambial region tissues in both aspen (Populus tremula, denoted poplar) and Scots pine (Pinus sylvestris) trees forming reaction wood, using tangential cryosectioning combined with sensitive gas chromatography-mass spectrometry analysis. Moreover, we have documented the kinetics of IAA during reaction wood induction in these species. Our analysis of endogenous IAA demonstrates that reaction wood is formed without any obvious alterations in IAA balance. This is in contrast to gravitropic responses in roots and shoots where a redistribution of IAA has been documented. It is also of interest that cambial growth on the tension wood side was stimulated without an increase in IAA. Taken together, our results suggest a role for signals other than IAA in the reaction wood response, or that the gravitational stimulus interacts with the IAA signal transduction pathway.

Place, publisher, year, edition, pages
ASPB Publications, 2004
National Category
urn:nbn:se:umu:diva-79572 (URN)10.1104/pp.104.038927 (DOI)000221420800024 ()
Available from: 2013-08-23 Created: 2013-08-23 Last updated: 2014-02-19Bibliographically approved

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