Articles
PEROXIDASES AND WALNUT (Juglans nigra L.) WOOD COLOURING
Article number
544_45
Pages
339 – 344
Language
English
Abstract
In the frame of the European research program W-BRAINS, we have jointly developed biochemical and histochemical approaches to characterise walnut wood (Juglans nigra L.) peroxidases and their role in heartwood colouring.
In this paper, we will mainly present histochemical results.
Peroxidasic activity have been revealed in situ using guaiacol as a substrate whereas the corresponding proteins have been localized by immunohistochemistry.
Peroxidasic activity is present in bark, cambium and sapwood but, in this last tissue, its localization is characteristic as it is only found in the ray cells.
It likely concerns cationic peroxidase forms as shown by electrophoresis and purification on column chromatography.
Peroxidasic activity decreases gradually in the last internal sapwood rings wich corresponds to the transition zone between sapwood and heartwood.
No activity was found in the heartwood, where coloured polymeric compounds appear.
These variations have been regularly observed according to the season, but the relative importance of peroxidasic activity in the different sapwood zones (external, middle and transition zones) seem to vary between winter and the growth period.
The presence of tyloses inside the vessels of the internal sapwood zone has been shown using scanning electron microscopy.
Peroxidase protein was revealed in these tyloses by immunohistochemistry but, in contrast to xylem rays peroxidase, it doesnt seem to be very reactive towards guaiacol and its participation to phenolic oxidation is still under discussion.
In this paper, we will mainly present histochemical results.
Peroxidasic activity have been revealed in situ using guaiacol as a substrate whereas the corresponding proteins have been localized by immunohistochemistry.
Peroxidasic activity is present in bark, cambium and sapwood but, in this last tissue, its localization is characteristic as it is only found in the ray cells.
It likely concerns cationic peroxidase forms as shown by electrophoresis and purification on column chromatography.
Peroxidasic activity decreases gradually in the last internal sapwood rings wich corresponds to the transition zone between sapwood and heartwood.
No activity was found in the heartwood, where coloured polymeric compounds appear.
These variations have been regularly observed according to the season, but the relative importance of peroxidasic activity in the different sapwood zones (external, middle and transition zones) seem to vary between winter and the growth period.
The presence of tyloses inside the vessels of the internal sapwood zone has been shown using scanning electron microscopy.
Peroxidase protein was revealed in these tyloses by immunohistochemistry but, in contrast to xylem rays peroxidase, it doesnt seem to be very reactive towards guaiacol and its participation to phenolic oxidation is still under discussion.
Publication
Authors
L. Dehon, C. Chalies, A. Fleuriet, J.J. Macheix
Keywords
walnut, Juglans nigra, peroxidase, heartwood, transition zone
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