Journal of Experimental Botany, Vol. 51, No. 349, pp. 1395-1401,
August 2000
© 2000 Oxford University Press
Original Paper |
A comparison of proteins from the developing xylem of compression and non-compression wood of branches of Sitka spruce (Picea sitchensis) reveals a differentially expressed laccase
Unit of Plant Biochemistry, Biochemistry and Cell Biology Division, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, UK
Received 12 January 2000; Accepted 20 April 2000
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Abstract |
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Soluble and cell wall-associated proteins were extracted from the developing xylem of the compression and non-compression sides of branches of Sitka spruce (Picea sitchensis (Bong) Carr.) by an identical procedure. Equal amounts of proteins were separated by SDS-PAGE, and polypeptides were identified that were more abundant in soluble and cell wall-associated extracts from the developing xylem of either compression or non-compression wood. Two polypeptides (at apparent Mrs of 48 kDa and 120 kDa) that were more adundant in cell wall-associated extracts of the developing xylem of the compression tissues were selected for amino-terminal protein sequencing. The 48 kDa polypeptide yielded an amino-terminal sequence that had no homology with known protein, gene or EST database sequences. The amino-terminal sequence of the 120 kDa polypeptide was homologous to a number of laccase-type polyphenol oxidases (EC 1.10.3.2) thought to be involved in lignin biosynthesis in trees. Using non-denaturing SDS-PAGE, the 120 kDa laccase was confirmed as a major oxidase activity in extracts of lignifying compression xylem but it was barely detectable in the non-compression extracts where an 85 kDa oxidase was the predominant activity. The differential expression of oxidases in compression and non-compression xylem is discussed.
Key words: Cell wall proteins, compression wood, lignification, Picea, xylogenesis.
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Introduction |
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Compression wood is formed in stems of conifers as a corrective reaction to a bending from the perpendicular and is formed naturally on the underside of horizontally orientated branches (Fahn, 1982
). Compression wood differs from opposite or non-compression wood in the ultrastructure of its tracheids and in the structure and composition of their secondary cell walls (Timell, 1973, 1986). Compression wood tracheids are uniform and lack the differences found between earlywood and latewood tracheids of non-compression wood. They are generally shorter, are more rounded and have characteristic intercellular spaces. The secondary cell walls of compression wood tracheids are noticeably thicker, but they are composed of only two layers (S1 and S2) compared with three layers in non-compression wood. The cell walls of compression wood tracheids contain more lignin, less cellulose and altered levels of matrix hemicelluloses including unique polysaccharides. Approximately 90% of lignin is present in the secondary cell wall layers, particularly in the lumen side of the S2 layer [S2(L)], with correspondingly less lignin in the middle lamella and primary cell wall. Compression wood lignin also has an elevated content of p-hydroxyphenylpropane units (Monties, 1989) with altered inter-unit bonding compared to non-compression wood (Nimz et al., 1981). As a consequence of these differences in structure and composition, compression wood has altered physical properties that impinge on its value as timber or pulp. The wood is generally denser but more brittle and suffers from enhanced longitudinal shrinkage. Groundwood and sulphite pulps are inferior to those from non-compression wood (Dinwoodie, 1981). The formation of compression and non-compression wood follows a similar developmental programme, from production of cambial initials through enlargement and secondary wall deposition, maturation to apoptosis, but the tracheids differ greatly in their ultrastructure, rate of growth, cell wall structure and composition. The phenotypes of non-compression and compression wood must result from the differential expression of the same genotype and this illustrates the inherent plasticity of wood cell development. The differentially expressed genes may control cell shape and cell wall structure and the comparison of compression and non-compression wood development may be useful to identify genes involved in these processes. In this paper, a comparative protein-based approach to identify proteins that are specifically expressed in developing xylem from the compression and non-compression sides of branches of Sitka spruce is reported.
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Materials and methods |
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Plant material
Branches (maximum 15 cm diameter) of Sitka spruce (Picea sitchensis (Bong) Carr.) were obtained from a single clone in the Forest Research clone bank at Ledmore, Perth and Kinross, Scotland, in late May 1998. In the laboratory, the branches were cut into approximately 50 cm lengths, the bark removed and the developing xylem was carefully scraped from the old wood on the compression and non-compression sides of each branch and frozen. The scraped tissues contained only enlarging and differentiating xylem cells. The extent of formation of compression wood on the underside of branches was estimated by its darker colour.
Extraction procedure
Compression and non-compression tissue (~100 g per extraction) was extracted by the method outlined previously (Deighton and McDougall, 1998). The compression and non-compression samples were extracted using the same set of buffers and under identical conditions. In brief, the tissue was homogenized in ice-cold homogenization buffer [25 mM MOPS pH 7.0 containing 0.5% (v/v) polyvinylpyrrolidine (PVP) and 0.5 mM phenylmethylsulphonyl fluoride (PMSF)] using a Waring blender then an Ultra-Turrax disintegrator. The soluble fraction was obtained after filtration through glass-fibre filters (Whatman GF/A). The insoluble residues were re-homogenized in fresh buffer that lacked both PVP and PMSF, these filtrates were discarded and the entire procedure was repeated three times. The insoluble residues (crude cell walls) were then extracted with 25 mM MOPS, pH 7.0, containing 200 mM CaCl2 (ConA buffer) for 1 h on ice with stirring to obtain the cell wall extracts. The use of high-salt buffers to enrich cell wall-associated proteins is a well-known technique (Fry, 1988).
Portions of the cell wall extracts were applied to small (5–7 ml bed volume) Concanavalin-A Sepharose (Pharmacia Ltd) columns and the eluate discarded. After a wash with a 5-fold column volume of ConA buffer, the ConA-bound fraction, which is enriched in cell wall-associated glycoproteins (McDougall, 1997), was eluted using equal volumes of ConA buffer containing 100 mM 
-methyl mannoside.
Analytical SDS-PAGE
Protein content was measured by the dye-binding method (Bradford, 1976). Proteins in extracts (25 or 50 µg) were precipitated by the addition of a 2.5-fold (v/v) excess of cold (-20 °C) acetone, mixed well then stored overnight at -20 °C and collected by centrifugation (10 000 g, 5 min) in a microfuge. The precipitated proteins were then redissolved in SDS-PAGE sample buffer, heated at 95 °C for 5 min then applied to SDS-PAGE. This technique was carried out using a Mini-Protean II slab gel system according to the makers' instructions (Bio-Rad, Hemel Hempstead, UK). Both prestained markers (broad range, New England Biolabs, Hitchin, UK) and silver-stain protein markers (broad range, Bio-Rad) were used for molecular weight estimation and gels were stained using the Bio-Rad silver-stain method.
The silver-staining intensity of polypeptides in the non-compression and compression extracts was compared. To overcome sample-to-sample and gel-to-gel variation, only polypeptides that were consistently more abundant in six replicate gels were noted. The pattern of polypeptides was also compared after SDS-PAGE in 10% and 12.5% acrylamide gels to ensure that polypeptides in the compression and non-compression extracts co-electrophoresed under different conditions.
Non-denaturing SDS-PAGE (ND SDS-PAGE)
This procedure was carried out as described before (Richardson et al., 1997). The procedure was similar to conventional SDS-PAGE but samples were prepared in buffer lacking ß-mercaptoethanol and SDS and were not boiled. Marker proteins were boiled to ensure that they were denatured. Gels were stored overnight at 8 °C before use to quench endogenous oxidants. Running buffer was chilled prior to use and gels were run at 8 °C to maintain enzyme activity. After normal electrophoresis, oxidase-like activity was detected using either 6.9 mM -naphthol/8.4 mM N,N,N',N'-tetramethyl p-phenylene diamine (-naphthol/TMPD) or 0.2 mM diaminofluorene (DAF) in 100 mM sodium acetate buffer pH 5.0. The pattern of oxidase-like activities was the same using either substrate and was not influenced by the addition of 100 µg ml-1 catalase (Sigma product no. C-30). Six replicate gels were run to confirm the consistency of the pattern of oxidase-like activities. Staining was complete within 20 min and, after oxidase-like polypeptides had been noted, peroxidase activity was visualized by the addition of 1 mM hydrogen peroxide.
Amino-terminal protein sequencing
Equal amounts of protein (100–200 µg) from compression and non-compression extracts were precipitated using acetone then prepared in Nu-PAGE sample buffer according to the manufacturer's instructions (NOVEX, San Diego, USA). The samples were separated by electrophoresis in pre-cast gradient (4–12% polyacrylamide) gels using the Nu-PAGE MES running buffer. The gel was blotted onto PVDF membrane using the Nu-PAGE blotting system and stained with Amido black. The abundance of target polypeptides was checked against initial silver-staining results and suitable polypeptides were excised for protein sequencing. The amino-terminal sequence of the excised polypeptides was determined using a PROCISE 492 protein sequencer using a modified Edmann degradation method optimized for PVDF blots (Applied Biosystems, Warrington, UK).
Sequence similarities were determined using the ‘BLITZ’ method against the non-redundant protein and DNA databases maintained by the European Bioinformatics Institute (http://www2.ebi.ac.uk/bic-sw). Similarities to non-redundant EST sequences were determined using the BLASTN series of programmes using the database of expressed sequence tags (ESTs) maintained by the National Centre for Biotechnology Information (http://www2.ncbi.nih.gov/dbEST) and the Loblolly pine cDNA sequence analysis project jointly run by the University of Minnesota and North Carolina State University (http://www.cbc.umn.edu/ResearchProjects/index.html). The positions of N-terminal residues of DNA sequences were predicted using the SignalP programme (http://www. cbs.dtu.dk/services/SignalP) and sequences were retrieved from ExPASy Geneva (http://www.expasy.ch/srs5).
Assays for oxidase activity, monolignol oxidase activity and protein content
Oxidase activity was determined by measuring the formation of the oxidized chromophore of 2, 2'-azinobis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) at 420 nm over a fixed period (Sterjiades et al., 1992). Monolignol oxidase activity was measured by the decline in Amax of the three monolignols (coniferyl alcohol, 262 nm; sinapyl alcohol, 270 nm; p-coumaryl alcohol, 260 nm) over a fixed period. Each monolignol was present at 0.2 mM in 100 mM sodium acetate pH 5.0 and the controls lacked enzyme. The products of monolignol oxidation also absorb at these maxima so reductions in Amax cannot be related directly to moles of monolignol oxidized. Coniferyl alcohol and sinapyl alcohol were purchased from Sigma Chemical Co. Ltd and pure p-coumaryl alcohol was a gift from Ashley Wallace and Dr Alistair Murray, Chemistry Department, University of Dundee.
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Results |
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Polypeptides at apparent Mr values of 66, 62, 58, and 47 kDa were more abundant in the soluble extracts of the compression tissue and the polypeptides at 66 kDa and 62 kDa and were barely detected in the non-compression extracts (Fig. 1
; compare lanes A and B). The polypeptides at 60, 54, 46, 44, and a doublet at 42 kDa were more abundant in the soluble extracts of the non-compression tissue, but none of these polypeptides was unique to the non-compression tissue.
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Polypeptides at apparent Mr values of 120, 78, 60, 54, and 48 kDa were more abundant in the cell wall extracts from compression tissue, but no polypeptide was more abundant in the equivalent non-compression extract (Fig. 1
; compare lanes C and D). A polypeptide with an apparent Mr of 120 kDa was much more abundant in the ConA-bound extract of the compression tissue whereas a polypeptide at 34 kDa was more abundant in the ConA-bound extract of the non-compression tissue (Fig 1; compare lanes E and F). There were differences in the pattern of polypeptides in the cell wall extracts and their ConA-bound counterparts (compare lanes C and E, non-compression; lanes D and F, compression) which indicates that not all of the proteins in the cell wall-associated extracts bind to this lectin. For example, the polypeptide at 78 kDa, which was abundant in the cell wall extract from the compression tissue (Fig. 1; lane D second arrow from top), was not present in the corresponding ConA-bound extract (Fig. 1; lane F).
Polypeptides that were more abundant in the high salt extracts (48 kDa) and the ConA-bound extracts (120 kDa) from compression wood xylem (Fig. 1) were selected for amino-terminal sequencing. The 48 kDa polypeptide yielded an amino-terminal sequence that had no significant homology with any sequence in DNA, protein or EST databases (Table 1). The 120 kDa polypeptide was much more abundant in the extracts obtained from the cell walls of compression tissue using high salt (Fig. 1; lane C and D) and the corresponding ConA-bound extract than the similar extracts from non-compression tissue (Fig. 1; lane E and F). This strongly suggests that this polypeptide was a cell wall-associated glycoprotein (McDougall, 1997). The compression abundant 120 kDa polypeptide yielded an amino-terminal sequence that was homologous with a number of plant laccases (Table 1). The greatest homology was with one of the four laccase genes from the developing xylem of Liriodendron tulipifera, laccase 2–4 (65% identity and 85% similarity), whereas the other Liriodendron genes had lower homology (Lafayette et al., 1999). The Sitka sequence also had considerable homology to an Arabidopsis EST for a putative laccase (T9I4.21), a laccase from tobacco (Kiefer-Meyer et al., 1996) and a laccase (Poplar-110) from poplar xylem (Ranocha et al., 1999). In addition, the amino-terminal sequence of the Sitka protein could be aligned exactly with the amino-terminal residues predicted (Nielsen et al., 1997) or observed for these proteins.
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Moreover, the 120 kDa polypeptide had homology (53% identity) with an EST sequence from the developing xylem of compression wood of Loblolly pine (Pinus taeda) which, in turn, had considerable homology to other plant laccase genes over its full sequence (Allona et al., 1999
). This confirms that the 120 kDa polypeptide is a conifer laccase. This is the first report of a protein sequence of a conifer laccase although a laccase has been purified (Bao et al., 1993) and laccase-like sequences have been identified in EST programmes from Loblolly pine (Allona et al., 1999).
The total and specific oxidase activities of the cell wall-associated extracts from the developing compression and non-compression xylem were similar (Table 2). This suggests that the non-compression extracts contain a different set of oxidases that compensate for the over-abundance of the 120 kDa laccase in the compression extracts.
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Non-denaturing SDS-PAGE was used to identify oxidase-like activities in the ConA-bound extracts from compression and non-compression xylem. Three oxidase-like activities with apparent Mr values of 128, 85 and 60 kDa were readily identified in the compression extracts (Fig. 2
, lane B, filled arrows) whereas the non-compression extract appeared to contain only the 85 and 60 kDa oxidase-like activities (Fig. 2, lane A, filled arrows). In fact, the 128 kDa oxidase-like activity was present in the non-compression extract but it was very faint and was more readily visualized after prolonged (1 h) staining.
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The oxidase-like activities with apparent Mr values of 128 and 85 kDa did not darken upon the addition of hydrogen peroxide whereas the diffuse activity at around 60 kDa darkened and a peroxidase activity at around 40 kDa appeared (results not shown). This confirms that the 128 and 85 kDa oxidase-like activities were not caused by peroxidase activity.
As proteins often migrate aberrantly under non-denaturing conditions (Richardson et al., 1997), the apparent Mr values quoted are only guides to the actual masses of the polypeptides responsible for these activities. Nevertheless, when the oxidase-like activity at 128 kDa was eluted and re-run on analytical SDS-PAGE, it co-electrophoresed with the 120 kDa polypeptide in the compression ConA-bound extracts (results not shown). This suggests that the 128 kDa oxidase-like activity was caused by the 120 kDa laccase identified above. The oxidase-like activity at 85 kDa may be similar to an oxidase previously identified in extracts of developing xylem of Sitka spruce by ND SDS-PAGE (Richardson et al., 1997).
The ConA-bound extracts from the compression and non-compression tissues had similar oxidase activity against ABTS, but they had different abilities to oxidize monolignols (Table 3). Both extracts had the same order of preference (sinapyl alcohol>coniferyl alcohol> p-coumaryl alcohol), but the compression extract was less able to oxidize coniferyl alcohol than the non-compression extract.
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Discussion |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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The comparative protein-based approach identified a number of cell wall-associated proteins that were more abundantly expressed in the developing xylem of the compression or non-compression tissues of branches of Sitka spruce. These proteins may influence the development of the differences in wall structure characteristic of compression wood tracheids, and are targets for protein sequencing. A simple one-dimensional electrophoretic separation was sufficient to identify target proteins in the cell wall-associated extracts. However, it is clear that more powerful, two dimensional methods using isoelectric focusing and SDS-PAGE, such as those employed by Sitbon et al. in their study of proteins expressed during cambial reactivation in Scots pine (Sitbon et al., 1993
), would be required to resolve the large number of proteins in the soluble extracts.
Two compression xylem-abundant polypeptides were sequenced. The sequence of 48 kDa polypeptide had no significant amino-terminal homology with known sequences in protein, DNA or EST databases. However, this lack of homology is not unexpected. A recent survey of cell wall-associated proteins from suspension-cultured plant cells using one-dimensional SDS-PAGE (Robertson et al., 1997) identified some enzymes by homology of their amino-terminal protein sequence with database sequences. Moreover, approximately half of the sequenced proteins had no homology to sequences in protein, EST or DNA databases. Considering that many proteins that have powerful effects on cell wall properties [e.g. XET (Fry, 1995) and expansins (Cosgrove, 1997)] have been found to be cell wall-associated, these unique proteins represent a large reservoir of enzymes with unknown but potentially commercially interesting properties.
The 120 kDa polypeptide was demonstrated to be a laccase-type polyphenol oxidase (EC 1.10.3.2) by homology of its amino-terminal protein sequence with known plant laccase sequences. Further examination using non-denaturing SDS-PAGE also suggested that this laccase was a major oxidase activity in the compression xylem extracts. In comparison, the 120 kDa laccase activity could barely be detected in the non-compression xylem extracts where the predominant activity was an 85 kDa oxidase which may be similar to the oxidase previously identified (Richardson et al., 1997) and purified (McDougall, 1998) from developing Sitka xylem. Although a general elevation of the levels of lignin biosynthetic enzymes has been reported (Kutsuki and Higuchi, 1981; Zhang and Chiang, 1997) in the more heavily lignified compression wood xylem, the difference in abundance of the 120 kDa and 85 kDa oxidases suggests differential expression of oxidase genes in developing compression and non-compression xylem. Different sets of laccase-like oxidase isoforms were reported in extracts of the lignifying xylem from the upper and basal portions of tobacco stems (Richardson and McDougall, 1997). Lafayette et al. demonstrated that four laccase genes were differentially expressed in the developing xylem of Liriodendron tulipifera (Lafayette et al., 1999) and it seems likely that other families of laccase genes in poplar (Ranocha et al., 1999) and tobacco (Kiefer-Meyer et al., 1996) are also subject to site- or developmental-specific expression. Allona et al. reported six laccase-like genes in their survey of ESTs from the developing xylem of compression wood of Loblolly pine (Pinus taeda) (Allona et al.,1999). However, the comparative level of expression of laccases in compression and non-compression tissues was not reported.
This differential expression of oxidases in the lignifying, developing compression and non-compression xylem suggests separate functions for these enzymes. As well as an elevated lignin content, compression wood tracheids have a higher content of p-hydroxyphenylpropane units, derived from p-coumaryl alcohol, and lower content of guaiacyl units, derived from coniferyl alcohol, than non-compression wood (Timell, 1986; Monties, 1989). Although the compression and non-compression extracts were equally able to oxidize p-coumaryl alcohol, the compression extracts were less able to oxidize coniferyl alcohol. The greater abundance of the 85 kDa oxidase activity in the non-compression extracts indicates that it may be more able to oxidize coniferyl alcohol. This observation supports the theory proposed by Dean et al. that the expression of specific laccase isoforms, with different redox potentials, may be linked to the deposition of syringyl-rich or guaiacyl-rich lignins in different lignifying tissues (Dean et al., 1998).
Other groups have used comparative approaches to discover differentially expressed genes in the developing xylem of reaction versus normal wood. For example, Leple et al. intimated their use of a subtractive cDNA-AFLP-based strategy to identify differentially expressed mRNAs in tension and non-tension woods from poplar (Leple et al., 1999). Allona et al. prepared subtraction libraries specific for genes expressed in either compression or non-compression xylem using cDNA libraries from developing xylem of compression and non-compression wood of Loblolly pine (Pinus taeda) (Allona et al., 1999). They found that most sequences with homology to lignin biosynthetic enzymes were noted only in the subtraction libraries specific for the more heavily lignified compression wood.
These mRNA/cDNA-based methods and the protein-based approach share some basic features. They require a comparative method to screen out genes/proteins involved in mundane ‘house-keeping’ functions and they depend on homology searches against protein, EST and DNA sequence databases to identify the differentially expressed genes/proteins. In addition, unique genes/proteins present much the same problems. On the other hand, unlike cDNA/mRNA-based methods, the study of expressed proteins can give some idea of post-translational modifications of proteins. For example, in this study, binding to Concanavalin A was used to produce a subset of cell wall-associated glycoproteins (McDougall, 1997). The careful use of other specific extraction methods could enrich proteins from other subcellular locales, such as integral membrane proteins (Tani et al., 1998). The subpopulations of proteins obtained may be more easily compared and completely resolved for sequencing (Robertson et al., 1997) than the thousands of proteins that make up the complement of expressed proteins or ‘proteome’ (Anderson and Anderson, 1998) of developing xylem cells (Sitbon et al., 1993)
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Acknowledgments |
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I thank Andrew Richardson and Julie Duncan for their hard work, Heather Ross for help with protein sequencing and Professor Howard V Davies for his support. I also thank Dr Ian M Morrison for his helpful comments. I am indebted to Dr Steve Lee of Forest Research, Forestry Commission for access to the Sitka spruce clonebank. The Scottish Crop Research Institute receives grant-in-aid from the Scottish Executive Rural Affairs Department.
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Notes |
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1 Fax: +44 1382 562426. E-mail: gmdou{at}scri.sari.ac.uk
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Abbreviations |
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ABTS, 2, 2'-azino bis (3-ethylbenzothiazoline-6-sulphonic acid); ConA, Concanavalin A; DAF, diaminofluorene; EST, expressed sequence tag; ND SDS-PAGE, Non-denaturing SDS-PAGE; PMSF, phenylmethylsulphonyl fluoride; PVP, polyvinylpyrrolidone; TMPD, N,N,N',N'-tetramethyl p-phenylene diamine..
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References |
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TopAbstractIntroductionMaterials and methodsResultsDiscussionReferences |
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Allona I, Quinn M, Shoop E, Swope K, St Cyr S, Carlis J, Riedl J, Retzl E, Campbell MM, Sederoff RR, Whetten RW.1999. Analysis of xylem formation in pine by cDNA sequencing. Proceedings of the National Academy of Sciences, USA 95, 9693–9698.
Anderson NL, Anderson NG.1998. Proteome and proteomics: new technologies, new concepts, and new words. Electrophoresis 19, 1853–1861.[Web of Science][Medline]
Bao W, O'Malley DM, Whetten R, Sederoff RR.1993. A laccase associated with lignification in Loblolly pine xylem. Science 260, 672–674.
Bradford MM.1976. A rapid and sensitive method for the detection of microgram amounts of protein utilising the principle of protein–dye binding. Analytical Biochemistry 7, 248–256.
Cosgrove DJ.1997. Assembly and enlargement of the primary cell wall in plants. Annual Review of Cell and Developmental Biology 13, 171–201.[Web of Science][Medline]
Dean JFD, LaFayette PR, Rugh C, Tristam AH, Hoopes JT, Eriksson K-EL, Merkle SA.1998. Laccases associated with lignifying vascular tissues. In: Lignin and lignin biosynthesis. American Chemical Society series no. 597, 96–108.
Deighton N, McDougall GJ.1998. Coniferyl alcohol oxidase operates via a free radical intermediate. Phytochemistry 48, 601–606.
Dinwoodie JM.1981. Timber, its nature and behaviour. London: Van Nostrand Reinhold.
Fahn A.1982. Plant anatomy, 3rd edn. London: Pergamon Press.
Fry SC.1998. The growing plant cell wall: chemical and metabolic analysis. Essex, UK: Longman.
Fry SC.1995. Polysaccharide-modifying enzymes in the plant-cell wall. Annual Review of Plant Physiology and Plant Molecular Biology 46, 497–513.[Web of Science]
Hubbard SC, Ivatt RJ.1981. Synthesis and processing of asparagine-linked oligosaccharides. Annual Review of Biochemistry 50, 555–583.[Web of Science][Medline]
Kiefer-Meyer M-C, Gomord V, O'Connell A, Halpin C, Faye L.1996. Cloning and sequence analysis of laccase-encoding cDNA clones from tobacco. Gene 178, 205–207.[Web of Science][Medline]
Kutsuki H, Higuchi T.1981. Activities of some enzymes of lignin formation in reaction wood of Thuja orientalis, Metasequoia glyptostroboides and Robinia pseudoacacia. Planta 152, 365–368.
Lafayette PR, Eriksson K-EL, Dean JFD.1999. Characterization and heterologous expression of laccase cDNAs from xylem tissues of yellow-poplar (Liriodendron tulipfera). Plant Molecular Biology 40, 23–35.[Web of Science][Medline]
Leple J-C, Gayon R, Pilate G.1999. Identification of differentially expressed mRNA during tension wood formation in poplar using a AFLP-based strategy. Journal of Experimental Botany 50, Supplement, 32.
McDougall GJ.1997. Procedure for selection of cell wall-associated glycoproteins. Phytochemistry 45, 633–636.
McDougall GJ.1998. Purification of coniferyl alcohol oxidase from lignifying xylem of Sitka spruce using immobilised metal affinity chromatography. Journal of Plant Physiology 153, 539–544.
Monties B.1989. Lignins. In: Harborne JB, ed. Methods in plant biochemistry, Vol. 1. London: Academic Press, 113–157.
Nielsen H, Engelbrecht J, Brunak S, von Heijne G.1997. Identification of prokaryotic and eukaryotic signal peptides and prediction of their cleavage sites. Protein Engineering 10, 1–6.
Nimz HH, Robert D, Faix O, Nemr DW.1981. Carbon-13 NMR spectra of lignin 8. Structural differences between the lignins of hardwoods, softwoods, grasses and compression wood. Holzforschung 35, 16–26.
Ranocha P, McDougall GJ, Hawkins S, Sterjiades R, Borderies G, Stewart D, Cabanes-Macheteau M, Boudet AM, Goffner D.1999. Biochemical characterization, molecular cloning and expression of laccases—a divergent gene family in poplar. European Journal of Biochemistry 259, 485–495.[Web of Science][Medline]
Richardson A, McDougall GJ.1997. A laccase-like polyphenol oxidase from lignifying tobacco xylem. Phytochemistry 44, 229–235.
Richardson A, Stewart D, McDougall GJ.1997. Identification and partial characterisation of a coniferyl alcohol oxidase from lignifying xylem of Sitka spruce (Picea sitchensis). Planta 203, 35–43.
Robertson D, Mitchell GP, Gilroy JS, Gerrish C, Bolwell GP, Slabas AR.1997. Differential extraction and protein sequencing reveals major differences in patterns of primary cell wall proteins from plants. Journal of Biological Chemistry 272, 15841–15848.
Sterjiades R, Dean JFD, Eriksson K-EL.1992. Laccase from Sycamore maple (Acer pseudoplatanus) oxidizes monolignols. Plant Physiology 99, 1162–1168.
Sitbon F, Eklof S, Riding RT, Sandberg G, Olsson O, Little CHA.1993. Patterns of protein synthesis in the cambial region of Scots pine shoots during reactivation. Physiologia Plantarum 87, 601–608.
Tani H, Kamidate T, Watanabe H.1998. Aqueous micellar two-phase systems for protein separation. Analytical Sciences 14, 875–888.
Timell TE.1973. Ultrastructure of the dormant and active cambial zones and the dormant phloem associated with the formation of normal and compression woods in Picea abies (L.) Karst. Technical publication no. 80. Syracuse, New York: State University of New York.
Timell TE.1986. Compression wood in gymnosperms. Heidelberg, Germany: Springer-Verlag.
Zhang X-H, Chiang VL.1997. Molecular cloning of 4-coumarate coenzyme A ligase in Loblolly pine and the roles of this enzyme in the biosynthesis of lignin in compression wood. Plant Physiology 113, 65–74.[Abstract]
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