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Is the branch of Viburnum odoratissimum var. awabuki reaction wood? Unusual eccentric growth and various distributions of growth strain
Yue Wang
Last modified: 2009-06-25
Abstract
YUE WANG,1,3 JOSEPH GRIL1,2 and JUNJI SUGIYAMA1
1Laboratory of Biomass Morphogenesis and Information, Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan
2Laboratoire de M'ecanique et G'enie Civil, Universit'e Montpellier 2, CNRS, Montpellier, France
3Correponding author (wangyuekyoto@rish.kyoto-u.ac.jp)
Tel: +81-(0)774-38-3634
Fax: +81-(0)774-38-3635
Keywords: Growth eccentricity, reaction wood, microfibril angle, spring-back strain
Growth eccentricity and growth strains in the branches of Viburnum odoratissimum var. awabuki were measured. A pronounced growth promotion occurred on the lower side of most branches. On the other hand, growth strains based on a cumulative measurement showed various distribution patterns: for some branch, the values on both sides corresponded to a tensile growth stress typical of normal wood and for other branches, the values on the lower side corresponded to a compressive growth stress. Growth strains based on a direct measurement showed a distribution similar to that in compression wood for most branches. Although the growth strain of the branches based on two measurement methods was similar to that of normal wood and had different patterns, a relatively larger growth strain was observed on the upper side of the branches. Thus, eccentric growth occurred on the side opposite to the larger growth strain. To understand the function of eccentric growth on the lower side of branches, we examined several anatomical features of the branches and found that (1) the cell walls of both sides were lacking the gelatinous layer, (2) the microfibril angle measured by X-ray diffraction and polarizing light was small both on the upper side and the lower side, and (3) the vessel number and cell wall area did not change greatly. Anatomical features of the xylem did not differ obviously between the upper and lower sides of branches; however, the fibers were longer on the lower side than on the upper side. Although the existence of a mechanical function of the eccentric growth was thus not identified, these results suggest that the growth stress pattern and formation of branch architecture in V. odoratissimum differ from those observed in other woody angiosperms.
1Laboratory of Biomass Morphogenesis and Information, Research Institute for Sustainable Humanosphere, Kyoto University, Uji, Kyoto 611-0011, Japan
2Laboratoire de M'ecanique et G'enie Civil, Universit'e Montpellier 2, CNRS, Montpellier, France
3Correponding author (wangyuekyoto@rish.kyoto-u.ac.jp)
Tel: +81-(0)774-38-3634
Fax: +81-(0)774-38-3635
Keywords: Growth eccentricity, reaction wood, microfibril angle, spring-back strain
Growth eccentricity and growth strains in the branches of Viburnum odoratissimum var. awabuki were measured. A pronounced growth promotion occurred on the lower side of most branches. On the other hand, growth strains based on a cumulative measurement showed various distribution patterns: for some branch, the values on both sides corresponded to a tensile growth stress typical of normal wood and for other branches, the values on the lower side corresponded to a compressive growth stress. Growth strains based on a direct measurement showed a distribution similar to that in compression wood for most branches. Although the growth strain of the branches based on two measurement methods was similar to that of normal wood and had different patterns, a relatively larger growth strain was observed on the upper side of the branches. Thus, eccentric growth occurred on the side opposite to the larger growth strain. To understand the function of eccentric growth on the lower side of branches, we examined several anatomical features of the branches and found that (1) the cell walls of both sides were lacking the gelatinous layer, (2) the microfibril angle measured by X-ray diffraction and polarizing light was small both on the upper side and the lower side, and (3) the vessel number and cell wall area did not change greatly. Anatomical features of the xylem did not differ obviously between the upper and lower sides of branches; however, the fibers were longer on the lower side than on the upper side. Although the existence of a mechanical function of the eccentric growth was thus not identified, these results suggest that the growth stress pattern and formation of branch architecture in V. odoratissimum differ from those observed in other woody angiosperms.