Stress generation in the tension wood of poplar is based on the lateral swelling power of the G-layer.
The mechanism of active stress generation in tension wood is still not fully understood. To characterize the functional interdependency between the G-layer and the secondary cell wall, nanostructural characterization and mechanical tests were performed on native tension wood tissues of poplar (Populus nigra x Populus deltoids) and on tissues in which the G-layer was removed by an enzymatic treatment. In addition to the well-known axial orientation of the cellulose fibrils in the G-layer, it was shown that the microfibril angle of the S2-layer was very large (about 36 degrees). The removal of the G-layer resulted in an axial extension and a tangential contraction of the tissues. The tensile stress-strain curves of native tension wood slices showed a jagged appearance after yield that could not be seen in the enzyme-treated samples. The behaviour of the native tissue was modelled by assuming that cells deform elastically up to a critical strain at which the G-layer slips, causing a drop in stress. The results suggest that tensile stresses in poplar are generated in the living plant by a lateral swelling of the G-layer which forces the surrounding secondary cell wall to contract in the axial direction.
Goswami
Luna
L
Max Planck Institute of Colloids and Interfaces, Department of Biomaterials, 14424 Potsdam, Germany.
Dunlop
John W C
JW
Jungnikl
Karin
K
Eder
Michaela
M
Gierlinger
Notburga
N
Coutand
Catherine
C
Jeronimidis
George
G
Fratzl
Peter
P
Burgert
Ingo
I
D002473:Cell Wall / Q000502:physiology*; D004548:Elasticity; D020894:Microfibrils / Q000502:physiology*; D008855:Microscopy, Electron, Scanning; D032107:Populus / Q000502:physiology*; D012542:Scattering, Radiation; D013314:Stress, Mechanical; D013718:Tensile Strength