Effet de la dur�e d'application d'un stimulus gravitationnel 
sur la formation de bois de tension et de bois oppos� dans de jeunes pousses 
de peuplier (<i>Populus euramericana</i> cv `Ghoy')

Jin

et al. 2017

Sci Rep

In Populus, the transcripts of fasciclin-like arabinogalactan proteins (FLAs) are accumulated in tension wood (TW) xylem, however their biological functions in TW formation are largely unknown. In this work, we demonstrated that PtFLA6, one of poplar TW-associated PtFLAs, was abundantly expressed in TW, and mainly localized in differentiating G-fibers. The bended stems of PtFLA6 antisense transgenic poplar showed decreased transcripts of PtFLAs, including PtFLA6, and reduced PtFLA6 like proteins, leading to inhibited TW differentiation and formation. We also showed that gibberellin A3 (GA3) was enriched in the xylem of TW side, accompanied with a lowered level of PtRGA1, a poplar DELLA protein. When GA3 biosynthesis was restrained in the bended poplar stems by a GA biosynthesis inhibitor (daminozide), TW formation was obviously repressed, as a result of restricted PtRGA1 degradation, and reduced PtFLA6 like proteins and PtFLA expression. Further studies indicated that PtFLAs were negatively regulated by PtRGA1. This study suggests that PtFLAs play important roles in the poplar TW formation, possibly regulated by GA signaling.

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Fasciclin-like arabinogalactan proteins, PtFLAs, play important roles in GA-mediated tension wood formation in Populus

Jin

et al. 2017

Sci Rep

“…De très légères réorientations, dues à des éléments tels que le vent, la lumière, le poids propre, etc., peuvent interférer avec le stimulus artificiel. Ceci est d'autant plus vrai qu'il a été montré que [27], dans le cas de jeunes pousses de peuplier, le temps de présentation (temps néces-saire à l'intégration du stimulus) et le temps de latence (temps minimal, compté depuis l'induction du stimulus, nécessaire à l'apparition de modifications anatomiques) sont relativement courts. Enfin, il apparaît que la variation du pourcentage de bois de tension tend à diminuer quand le stimulus augmente.…”

Section: Quantification Du Bois De Tensionunclassified

“…Cela signifie que plus de la moitié des cellules cambiales ont réagi au stimulus gravitationnel. Les valeurs d'angle de l'arc de bois de tension, mesurées sur les pousses inclinées à 30°, correspondent exactement à celles obtenues précédemment sur un matériel végétal similaire [27]. Sur des pousses de saule inclinées à 30°, Robards [41] a mesuré un arc de bois de tension de 203°.…”

Section: Arc De Bois De Tensionunclassified

Effet de l?intensit� d?un stimulus gravitationnel induit artificiellement sur la croissance et la formation du bois de tension dans de jeunes pousses de peuplier (Populus euramericana cv ?Ghoy?)

Jourez

Vaïanopoulos²,

Hebert³

2003

Ann. For. Sci.

Self Cite

Résumé -La formation d'un tissu de bois de tension est induite artificiellement au moyen d'un stimulus gravitationnel obtenu en inclinant de jeunes pousses de l'année de Peuplier euraméricain cv 'Ghoy' à diverses intensités de 0 à 30° durant la saison de végétation. Au terme de l'expé-rimentation, il s'avère que l'allongement des pousses ainsi que l'angle de l'arc de bois de tension, ne sont pas affectés par l'intensité du stimulus. Au contraire, le redressement de l'axe, la quantité de fibres gélatineuses, la croissance secondaire sur écorce, la surface de la section et du xylème secondaire, les différents rayons caractéristiques, les diamètres sous écorce et l'excentricité de la moelle, répondent quantitativement à l'inclinaison. La quantité de bois de tension est corrélée au redressement, à la croissance secondaire sur écorce et à la croissance radiale sous écorce. Par ailleurs, la formation du bois de tension et l'excentricité réagissent au stimulus gravitationnel, sans pour autant être liés entre eux par une relation de cause à effet. Enfin, il existe une position naturelle d'équilibre des tiges, différente de la verticale, vers laquelle les pousses qui ont été déplacées, tentent de revenir en formant un tissu de bois de tension. stimulus gravitationnel / bois de tension / croissance / Populus euramericana cv 'Ghoy' Abstract -Effect of intensity of gravitational stimulus artificially induced on growth and tension wood formation in young shoots of poplar (P. euramericana cv 'Ghoy'). The formation of tension wood tissue is artificially induced by means of a gravitational stimulus obtained by inclining young shoots of poplar at different intensities, from 0 to 30°, during a growing season. At the end of the experiment, it appears that shoot elongation as well as the angle of tension wood arc are not affected by the stimulus intensity. In contrast, the upright reorientation of the axis, the amount of gelatinous fibres, the secondary growth over bark, the cross-section area of the stem and of the secondary xylem, the different rays, the diameter under bark and the pith eccentricity, react quantitatively to the lean intensity. The amount of tension wood is correlated with the upright reorientation, the secondary growth over bark and the radial growth under bark. Tension wood formation and eccentricity react to the gravitational stimulus but they are not causally linked. Finally, it exists a natural equilibrium position, different from the vertical, to which moved shoots try to return via the formation of a tension wood tissue. gravitational stimulus / tension wood / growth / Populus euramericana cv 'Ghoy'

“…These internal forces, referred to as growth stresses, are particularly intense in the longitudinal direction and are due to the maturation of the wood produced by radial growth and, more especially, to the natural longitudinal shrinkage it induces (Almeras et al 2008;Archer 1989;Boyd 1977;Constant and Nepveu 2007). In the case of mechanical stimulation (such as a disequilibrium in the field of gravity), an angular sector of the new ring can differentiate into reaction wood, a particular wood that generates considerably higher stresses than normal wood, especially in broadleaved species (Bamber 2001;Coutand et al 2007;Jourez and Avella-Shaw 2003). The asymmetry of reaction wood production leads to growth stress asymmetry that tends to curve the stem and to modify its orientation, for example, to counteract the effect of gravity and restore stem verticality (Almeras et al 2005;Huang et al 2010).…”

Section: Introductionmentioning

confidence: 98%

Impact of stand density on tree morphology and growth stresses in young beech (Fagus sylvatica L.) stands

Dassot

Constant²,

Ningre³

et al. 2014

Trees

Key message According to biomechanical processes, tree morphology (trunk inclination, height-to-diameter ratio and crown area) explains statistically silvicultural effects on growth stress variation. Abstract Growth stresses constitute the main mechanism allowing the tree to control its posture against its mechanical environment, but are also among the most important factors contributing to the depreciation of timber value. This study aimed at assessing the link between stand planting density and growth stress level in European beech (Fagus sylvatica) stands. Beech seedlings were planted in four plots corresponding to four planting densities: 2,500, 5,000, 10,000 and 40,000 stems/ha. They were left to grow for 26 years without any intervention, resulting in trees with highly different morphologies but of the same age and provenance. After 26 years of growth, both the tree morphology and growth stress indicators were measured on the standing trees in each plot and an attempt was made to establish a link between them. Our results showed that initial stand density influences growth stresses of the first order as a result of its impact on tree morphology. The best predictors of high growth stresses were high trunk inclination, high height-to-diameter ratio (slenderness factor) and low crown area. According to mechanosensing theories, these morphological criteria emphasised that growth stresses are due to a global mechanical stimulation rather than to local stem inclination alone. Research now has to be undertaken on new methods that combine the integrative assessment of tree morphology as well as its monitoring over time.