Abstract
BackgroundTension wood is a type of reaction wood in response to bending or leaning stem as a corrective growth process. Tension wood is formed by both natural and man-made processes. Most attractively, tension wood contains higher glucan content and undergoes higher enzymatic conversion to fermentable sugars. Here, we have employed structural techniques, small-angle neutron scattering (SANS) and wide-angle X-ray diffraction (WAXD) to elucidate structural and morphological aspects of tension wood conducive to higher sugar yields.ResultsSmall-angle neutron scattering data exhibited a tri-modal distribution of the fibril cross-sectional dimension. The smallest size, 22 Å observed in all samples concurred with the WAXD results of the control and opposite side samples. This smallest and the most abundant occurring size was interpreted as the cellulose elementary microfibril diameter. The intermediate size of 45 Å, which is most pronounced in the tension side sample and consistent with WAXD results for tension side sample, indicates association of neighboring elementary microfibrils to form larger crystallite bundles. The largest size 61 Å observed by SANS was however not observed by WAXD and therefore associated to mesopores.ConclusionsStructure and morphology of tension wood is different from control wood. Cellulose crystallinity increases, lignin content is lower and the appearance of mesopores with 61 Å diameter is observed. Despite the presence of higher crystalline cellulose content in tension side, the lower lignin content and may be combined with the abundance of mesopores, substantially improves enzyme accessibility leading to higher yields in cellulose digestion.
Highlights
Tension wood is a type of reaction wood in response to bending or leaning stem as a corrective growth process
The 2D pattern indicates that the cellulose fibrils are vertically aligned and the scattering in the equatorial direction represents the structural features of the cross-sectional dimension such as cross-sectional size and/or distance between neighboring fibrils
Our studies suggest that the method of applying tension stress, bending or leaning, cause no measureable difference to the cellulose fibril structure
Summary
Tension wood is a type of reaction wood in response to bending or leaning stem as a corrective growth process. Tension wood is formed by both natural and man-made processes. The primary function of the biopolymers is to form the structural framework of plants. These biopolymers mainly reside in the plant cell walls, primary and secondary. The cellulose microfibrils grow in a direction that deviates from the longitudinal axis of the cells. This angle called the microfibril angle, MFA, for the dominant layer S2 of the secondary cell wall is typically between 5° and 30°, while for the S1 and S3 layers, it is 50–70° and > 70°, respectively [1, 10]
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