Control of the kinematics of wood formation by a morphogenetic gradient
2015
Hartmann, Félix | Rathgeber, Cyrille | Fournier, Meriem | Moulia, Bruno | Laboratoire d'Etudes des Ressources Forêt-Bois (LERFoB) ; Institut National de la Recherche Agronomique (INRA)-AgroParisTech | Laboratoire de Physique et Physiologie Intégratives de l'Arbre Fruitier et Forestier (PIAF) ; Institut National de la Recherche Agronomique (INRA)-Université Blaise Pascal - Clermont-Ferrand 2 (UBP)
In conifers, tracheary elements (tracheids) are produced by the vascular cambium, which is an undifferentiated tissue lying between the bark and the wood already formed. In temperate zones, a succession of annual growth rings can be easily seen on the cross-section of a fallen tree. The radial structure of a tree ring is characteristic and repeated almost unchanged from one ring to the other. The mechanisms which regulate wood formation and lead to the typical growth ring structure are not known. At the tissue level, differentiating tracheids are organized into radial files. Along these files, several developmental zones can be observed (Fig. 1). It has been suggested by several experimental works that graded-concentration profiles of some biochemical signals could guide cells during their differentiation by providing them with positional information (Bhalerao and Fischer, 2014). This is the so-called “morphogenetic-gradient hypothesis”. The phytohormone auxin is the most prominent candidate as signaling molecule, but the role played by the peptide TDIF also got experimental support (Hirakawa et al., 2010). However, it is still not known whether a morphogenetic gradient can effectively control tissue growth and patterning. A developmental and biophysical approach relying on growth kinematics and on signal transport has thus been conducted through modelling to assess the hypothesis that this gradient could guide cell differentiation via concentration thresholds.
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