Summary Fifteen poplar cDNA encoding fasciclin‐like arabinogalactan proteins (PopFLAs) were finely characterized, whereas the presence of arabinogalactan proteins (AGPs) was globally assessed during wood formation. PopFLAs transcript accumulation was analysed through EST distribution in cDNA libraries, semi‐quantitative RT‐PCR, microarray experiment and Northern blot analysis. Similarly, AGPs contents were globally quantified by rocket electrophoresis. AGPs accumulation was further examined by Western blotting and immunocytolocalization. Ten PopFLAs were specifically expressed in tension wood (TW) and not expressed in the cambial zone. Rocket electrophoresis revealed important AGPs accumulation in TW xylem. An anti‐AGPs specific antibody recognized two proteins preferentially present in the cell wall‐bound fraction from TW. Immunocytochemistry revealed a strong labelling close to the inner part of the G‐layer of TW fibres. PopFLAs are expressed in xylem and many are up‐regulated in TW. It is suggested that some PopFLAs accumulating at the inner side of the G‐layer may have a specific function in the building of this layer. PopFLAs expression may therefore be linked to the specific mechanical properties of TW.

In functioning eucalypt ectomycorrhizas, biochemical alterations are accompanied by a differential accumulation of polypeptides including the synthesis of symbiosis-related proteins (JL Hilbert, Martin FM [1988] New Phytol 110: 339-346). In the present study, protein biosynthesis in the early stages of ectomycorrhiza formation on Eucalyptus globulus subsp. bicostata Kirkp. was examined using compatible and incompatible isolates of the basidiomycete Pisolithus tinctorius (Coker & Couch). Changes in polypeptide composition were observed within hours following contact of the compatible mycelium with the roots, well before the differentiation of typical symbiotic tissues. At this stage, at least seven symbiosis-related proteins (ectomycorrhizins) accumulated in root tissues. In vivo incorporation of [35S]methionine by ectomycorrhizas followed by electrophoresis of the labeled proteins revealed that most of these differences in polypeptide concentrations, including the ectomycorrhizin accumulation, are the result of differential protein biosynthesis rather than posttranslational modifications of the polypeptides. The initial development of eucalypt ectomycorrhizas, therefore, coincides with the synthesis of symbiosis-related proteins and the data presented here provide essential evidence to ascribe a functional developmental role to these proteins.Induction of ectomycorrhizal symbiosis on tree roots by soil fungi in the classes ascomycetes and basidiomycetes has been shown to be a highly evolved and complex process, requiring a fine-tuned interaction between compatible mycorrhizal fungi and their host plant (4,10,17). The fungus encodes the basic enzymatic machinery for absorbing, transporting, and assimilating major mineral ions (e.g. phosphate and inorganic nitrogen). The plant maintains a unique ecological niche that is necessary for fungal growth and devel-' This paper is dedicated to the memory of Prof. J. Harley and is the second paper of a series.

The presence of an alpha4-fucosyltransferase in plants was first deduced from the characterization of Lewis-a glycoepitopes in some N-glycans. The first plant gene encoding an alpha4-fucosyltransferase was recently cloned in Beta vulgaris. In the present paper we provide evidence for the presence of an alpha4-fucosyltransferase in A. thaliana by measurement of this glycosyltransferase activity from a purified microsomal preparation and by immunolocalization of Le(a) epitopes on glycans N-linked to glycoproteins located to the Golgi apparatus and on the cell surface. The corresponding gene AtFT4 (AY026941) was characterized. A unique copy of this gene was found in A. thaliana genome, and a single AtFT4 transcript was revealed in leaves, in roots, and at a lower extent in flowers. The coding sequence of AtFT4 gene is interrupted by two introns spanning 465 bp and 84 bp, respectively. The putative 393-amino-acid protein (44 kDa, pI: 6.59) contains an N-terminal hydrophobic region and one potential N-glycosylation site, but AtFT4 has poor homology (less than 30%) to the other alpha3/4-fucosyltransferases except for motif II. When expressed in COS 7 cells the protein is able to transfer Fuc from GDP-Fuc to a type 1 acceptor substrate, but this transferase activity is detected only in the culture medium of transfected cells

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