Tensile growth stress and lignin distribution in the cell walls of yellow poplar, Liriodendron tulipifera Linn.

Abstract

Five specimens that contained a continuous gradient of wood, from normal to tension wood regions, were collected from an inclined yellow poplar (Liriodendron tulipifera), and the released strain of tensile growth stress was quantified. Ultraviolet (UV) microspectrophotometry was used to examine the relationship between lignin distribution in the cell wall and the intensity of tensile growth stress. The UV absorption of the secondary wall and the cell corner middle lamella decreased with increasing tensile released strain (i.e., tensile growth stress). The UV absorption in the compound middle lamella region remained virtually constant, irrespective of the tensile released strain. The absorption maximum (λ max ) remained virtually constant in the secondary wall, the cell corner middle lamella, and the compound middle lamella region at 273-274, 277-278, and 275-278 nm respectively, irrespective of the tensile released strain. The ratios of the UV absorbance at 280 to 260 nm and 280 to 273 nm of the secondary wall decreased with increasing tensile released strain. The ratios in the cell corner and compound middle lamella region remained constant, irrespective of the tensile released strain. The lignin content of the secondary wall decreased, while the syringyl/guaiacyl ratio increased with increasing tensile released strain. Gelatinous fibers were not observed in the tension wood regions, but the secondary wall became gelatinous-layer-like, i.e., the lignin content and microfibrillar angle decreased and the cellulose content increased. A definite gelatinous layer seems to be important for generating greater tensile growth stress. It is concluded that a decrease in lignin and an increase in cellulose microfibrils parallel to the fiber axis in the secondary wall are necessary to produce large tensile growth stress.

Tree growth stress and related problems

“…Observations using the ultraviolet photomicroscope confirmed that the decrease of lignin concentration in tension wood of Liriodendron tulipifera occurs in the secondary wall of wood fibers from a zone where a large tensile L stress has been measured ( Fig. 10) [57]. In the case of rather primitive angiosperms like Magnoliaceae, large cellulose content and low MFA seem to produce a similar effect as the formation of distinctive G-layer in highly evolved eudicot species [43].…”

“…wall. UV absorbance in the secondary wall gradually decreases with an increase of tensile growth stress [57] that once a high tensile stress has been generated in the cellulosic network of the G-layer, late lignification does not significantly modify this pre-existing tension [59,60].…”

Chemical modification of secondary xylem under tensile stress in the stem ofLiriodendron tulipifera

“…This could be realized by applying forest biotechnology with its emphasis on ''fast-growing'' plantations with increased resistance against biotic and environmental stresses (Kwon et al 2001). In addition to its practical applications, yellow poplar is also regarded as a very important tree species, which has been frequently employed in studies of the evolution of flowering plants and of specific gene families, since it occupies an important phylogenetic position as a basal angiosperm that has retained a number of putatively ancestral morphological characteristics (Yoshida et al 2002;Liang et al 2007).…”

“…These chemical modifications of the secondary cell wall in tension wood appear to be at least partially associated with the formation of a gelatinous (G) layer, as the G-layer in the tension wood has been proposed to be specialized for the generation of larger tensile growth stress, primarily in tension wood formed in the upper region of the leaning stem and branches (Yamamoto et al 1993). Interestingly, anatomical analyses of yellow poplar tension wood have demonstrated that its fibers do not form a G-layer under tensile stress, differently from other angiosperms (Yoshida et al 2002). Therefore, it is a matter of great interest to determine whether alterations and modifications of the chemical composition of yellow poplar tension wood is consistent with those of other angiosperm species, which evidence a gelatinous layer in their tension wood fibers.…”

An Overview of Microfibril Angle in Fiber of Tension Wood

“…2B, 3B) [33][34][35][36][37][38]. In some species having no G-layer in reaction wood, it has been reported that microfibril angle of S2 layer decreased [15,[39][40][41][42] reported that the microfibril angle of S2 layer was very small (5 to 10 degrees) in reaction wood of Magnolia acuminate and Liriodendron tulipifera. In Magnolia obovata and M. kobus, the innermost surface of S2 layer of fiber tracheid wall also showed a small microfibril angle [41].…”