Maturation Stress Generation in Poplar Tension Wood Studied by Synchrotron Radiation Microdiffraction

Bruno Clair,Christian Riekel,Junji Sugiyama,Tancrède Alméras,Delphine Jullien,Gilles Pilate

doi:10.1104/pp.109.149542

Abstract

Tension wood is widespread in the organs of woody plants. During its formation, it generates a large tensile mechanical stress, called maturation stress. Maturation stress performs essential biomechanical functions such as optimizing the mechanical resistance of the stem, performing adaptive movements, and ensuring long-term stability of growing plants. Although various hypotheses have recently been proposed, the mechanism generating maturation stress is not yet fully understood. In order to discriminate between these hypotheses, we investigated structural changes in cellulose microfibrils along sequences of xylem cell differentiation in tension and normal wood of poplar (Populus deltoides x Populus trichocarpa 'I45-51'). Synchrotron radiation microdiffraction was used to measure the evolution of the angle and lattice spacing of crystalline cellulose associated with the deposition of successive cell wall layers. Profiles of normal and tension wood were very similar in early development stages corresponding to the formation of the S1 and the outer part of the S2 layer. The microfibril angle in the S2 layer was found to be lower in its inner part than in its outer part, especially in tension wood. In tension wood only, this decrease occurred together with an increase in cellulose lattice spacing, and this happened before the G-layer was visible. The relative increase in lattice spacing was found close to the usual value of maturation strains, strongly suggesting that microfibrils of this layer are put into tension and contribute to the generation of maturation stress.

Highlights

To cite this version: Bruno Clair, Tancrède Alméras, Gilles Pilate, Delphine Jullien, Junji Sugiyama, et al
In order to discriminate between these hypotheses, we investigated structural changes in cellulose microfibrils along sequences of xylem cell differentiation in tension and normal wood of poplar (Populus deltoides 3 Populus trichocarpa ‘I45-51’)
Analysis showed that this increase in lattice spacing is at least partly due to mechanical stress induced in cellulose microfibrils soon after their deposition, suggesting that the G layer directly generates and supports the tensile maturation stress in poplar tension wood

Summary

RESULTS

Typical diffraction patterns obtained from one tension wood and one normal wood sample are shown in Figures 2 and 3 (results for other samples are shown in Supplemental Data S2). Allel to the thickening of the cell wall During this phase, similar intensity profiles are observed for small MFA and large MFA in both normal wood and tension wood samples. For small MFA in tension wood, one can clearly see a progressive increase in lattice spacing in the first 600 mm after the cambium This increase is steep in the area where the innermost part of the cell wall, dominated by small MFA, diverges on the intensity signal (Fig. 3A). This area clearly corresponds to the development of the G layer. In most of the tension wood profiles, no or very little delay was observable between the deposition of cellulose (detected by intensity) and the increase in mean lattice spacing

DISCUSSION

CONCLUSION

MATERIALS AND METHODS