Contributions of bark and tension wood and role of the G-layer lignification in the gravitropic movements of 21 tropical tree species

Abstract

& Key message Gravitropic movements in angiosperm woody stems are achieved through the action of bark and/or wood motor, depending on the bark and wood fibre anatomy (with trellis structure or not; with G-layers or not). Bark motor is as efficient as wood motor to recover from tilting in young trees of 21 tropical species. & Context Angiosperm trees produce tension wood to control their orientation through changes in stem curvature. Tension wood is classified into 3 anatomical groups: with unlignified G-layer, with lignified G-layer and without G-layer. & Aims This study aimed at assessing whether this anatomical diversity reflects a diversity in efficiency of gravitropic movement. & Methods The study was conducted on tropical seedling from the three anatomical groups. Seedlings were staked and grown tilted. At the end of the experiment, changes in curvature when releasing the stem from the stake and when removing bark were measured. Three parameters were computed to compare the global efficiency of gravitropism (stem gravitropic efficiency) and the specific efficiency of motor mechanism based on wood (maturation strain of tension wood) and bark (standardized debarking curvature). & Results The maturation strain of tension wood was similar between species with unlignified and lignified G-layer. Species without G-layer exhibited low maturation strain and large debarking curvature, showing they rely on bark for gravitropism. Bark and wood achieved similar motor efficiency. & Conclusion Lignin does not affect the generation of tensile stress in the G-layer. Bark can be as efficient as wood as a motor of gravitropic movements.

Do woody vines use gelatinous fibers to climb?

“…Our frequent observations of extraxylary G‐fibers complement recent findings that extraxylary tissues play important roles in movements that were previously attributed solely to xylem. For example, experiments on artificially inclined trees demonstrated that bark also influences plant posture (Ghislain et al ., 2019a,b), and Lehnebach et al . (2020) showed that phloem G‐fibers arranged in a trellis network produce higher tensile stress than species with a phloem trellis network of ordinary fibers do.…”

Gelatinous fibers develop asymmetrically for posture support of bends and coils in common bean vine

“…2J). (1-5)-α-L-arabinan pectin side chains were not labeled in G-fibers (LM6; The G-layer is often cited as being mostly cellulosic and devoid of lignin, however recent reports indicate that lignification is more widespread than previously expected (Roussel and Clair, 2015;Ghislain and Clair, 2017;Ghislain et al, 2019). By double staining sections with safranin and astra blue (Bukatsch, 1972) we typically found that the G-layer was blue (unlignified), whereas the outer S-layers generally stained red (lignified) (Fig…”

Sustainable Wooden Skyscrapers for the Future Cities

“…• Change-generating tissue: This consists of a single layer of cells located between the bark and wood, which causes an increase in thickness [17]. A new growth ring is added annually to the trunk of the tree, and the number of rings indicates the age of the tree.…”