Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The mechanism for tree orientation in angiosperms is based on the production of high tensile stress on the upper side of the inclined axis. In many species, the stress level is strongly related to the presence of a peculiar layer, called G-layer, in the fibre wall. The structure of G-layer has been recently described as a hydrogel thanks to N2 adsorption-desorption isotherms of supercritically dried samples showing a high mesoporosity (pores size from 2 to 50 nm). This led us to revisit the concept of G-layer that was until now only described from anatomical observation. Adsorption isotherms of both normal wood and tension wood have been measured on six tropical species. Measurements show that mesoporosity is high in tension wood with typical thick G-layer while it is much less with thinner G-layer, sometimes no more than normal wood. The mesoporosity of tension wood species without G-layer is as low as in normal wood. Not depending on the amount of pores, the pore sizes distribution are always centred around 6-12 nm. These results suggest that, among species producing fibres with G-layer, large structural differences of G-layer exist between species
ISSN: 0022-0957

hal-00387861
https://hal.archives-ouvertes.fr/hal-00387861
DOI : 10.1093/jxp/erp133

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy B - Oxford Open Option A
Résumé :  
The mechanism for tree orientation in angiosperms is based on the production of high tensile stress on the upper side of the inclined axis. In many species, the stress level is strongly related to the presence of a peculiar layer, called the G-layer, in the fibre cell wall. The structure of the G-layer has recently been described as a hydrogel thanks to N2 adsorption-desorption isotherms of supercritically dried samples showing a high mesoporosity (pores size from 2-50 nm). This led us to revisit the concept of the G-layer that had been, until now, only described from anatomical observation. Adsorption isotherms of both normal wood and tension wood have been measured on six tropical species. Measurements show that mesoporosity is high in tension wood with a typical thick G-layer while it is much less with a thinner G-layer, sometimes no more than normal wood. The mesoporosity of tension wood species without a G-layer is as low as in normal wood. Not depending on the amount of pores, the pore size distribution is always centred around 6-12 nm. These results suggest that, among species producing fibres with a G-layer, large structural differences of the G-layer exist between species.
Journal of Experimental Botany

hal-01032161
https://hal.archives-ouvertes.fr/hal-01032161
DOI : 10.1093/jxb/erp133

Éditeur(s) : HAL CCSD Wiley
Résumé : International audience
In order to progress in the understanding of mechanical stress generation, the mesoporosity of the cell wall and its changes during maturation of poplar (Populus deltoides x P. nigra) tension wood (TW) and opposite wood (OW) were measured by nitrogen adsorption–desorption. Variations in the thickness of the gelatinous layer (G-layer) were also measured to clarify whether the mesoporosity change simultaneously with the deposition of the G-layer in TW. Results show that mesoporous structures of TW and OW were very similar in early development stages before the deposition of G-layers. With the formation of the S2 layer in OW and the G-layer in TW, the mesopore volume decreased steeply before lignification. However, in TW only, the decrease in mesopore volume occurred together with the pore shape change and a progressive increase in pore size. The different patterns observed in TW revealed that pores from G-layers appear with a different shape compared to those of the compound middle lamella, and their size increases duringthe maturation process until stabilising in mature wood. This observation strongly supports the hypothesis of the swelling of the G-layer matrix during maturation as the origin of maturation stress in poplar tension wood.
ISSN: 0028-646X

hal-01081834
https://hal.archives-ouvertes.fr/hal-01081834
https://hal.archives-ouvertes.fr/hal-01081834/document
https://hal.archives-ouvertes.fr/hal-01081834/file/Chang_al_Mesoporosity_changes_New-Phyto._2015.pdf
DOI : 10.1111/nph.13126

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : Increasing interest in understanding tension stress generation in tension wood with fibres having a gelatinous layer (G-layer) has focused attention on the specific role of this layer. To distinguish its contribution from those of other wall layers, the G-layer of wood sections was isolated by ultrasonication. The aim of this study was to assess the effect of sectioning and of the ultrasonic treatment on the mesoporosity of tension wood using nitrogen adsorption-desorption analysis. The results showed that the process of isolating the G-layer using ultrasonication strongly affects its mesoporosity. Most damage was found to occur during sectioning rather than as a result of the 15-min ultrasonic treatment.
ISSN: 0043-7719

hal-01601127
https://hal.archives-ouvertes.fr/hal-01601127
DOI : 10.1007/s00226-017-0890-0
PRODINRA : 401888

Éditeur(s) : HAL CCSD RSC Publishing
Résumé : International audience
Abstract View references (36)The size or alkyl chain length of cationic surfactants can be used to tailor both the pore morphology and the functionality or oxidation state of cobalt in silica materials. This work shows for the first time that these two mechanisms are interconnected. Cobalt oxide silica materials, with the same cobalt loading (Co:Si = 1:4), were prepared using an acid catalysed sol-gel method where the cobalt/surfactant ratio was systematically varied. The alkyl chain length of the cationic surfactant was also varied from 2 to 12 by using tetraethyl (C2-AB) ammonium bromide, and triethyl hexyl (C6-AB) and dodecyl trimethyl (C12-AB) ammonium bromides as the templating agents. Initial addition of C2-AB, C6-AB or C12-AB enhanced the oxidation of cobalt to cobalt (ii,iii) oxide in the xerogels. However, as more surfactant is added the enhancement effect is reversed and the cobalt (ii,iii) oxide content of the sample begins to decline. The point at which this transition occurs is a function of the alkyl chain length of the surfactant, with a longer chain indicating an earlier transition. Pore morphology was influenced in a similar fashion with the longer alkyl chain C12-AB surfactant undergoing an earlier transition (i.e. at lower concentrations) towards mesoporosity, than either of the smaller C2-AB and C6-AB surfactants. In both mechanisms it was the increased propensity of the C12-AB surfactant to aggregate (given its larger size and lower solubility) that was the controlling factor. This journal is © the Partner Organisations 2014.
EISSN: 2046-2069

hal-01683205
https://hal.univ-antilles.fr/hal-01683205
DOI : 10.1039/c4ra05934d