The influence of pre-steaming and lignin distribution on wood pellet robustness and ease of subsequent enzyme-mediated cellulose hydrolysis

We studied the influence of pre-steaming and lignin distribution on wood pellet robustness and ease of subsequent enzyme-mediated hydrolysis.

Hevea brasiliensis coniferaldehyde-5-hydroxylase (HbCAld5H) regulates xylogenesis, structure and lignin chemistry of xylem cell wall in Nicotiana tabacum

Key message The HbCAld5H1 gene cloned from Hevea brasiliensis regulates the cambial activity, xylem differentiation, syringyl–guaiacyl ratio, secondary wall structure, lignification pattern and xylan distribution in xylem fibres of transgenic tobacco plants. Abstract Molecular characterization of lignin biosynthesis gene coniferaldehyde-5-hydroxylase (CAld5H) from Hevea brasiliensis and its functional validation was performed. Both sense and antisense constructs of HbCAld5H1 gene were introduced into tobacco through Agrobacterium-mediated genetic transformation for over expression and down-regulation of this key enzyme to understand its role affecting structural and cell wall chemistry. The anatomical studies of transgenic tobacco plants revealed the increase of cambial activity leading to xylogenesis in sense lines and considerable reduction in antisense lines. The ultra-structural studies showed that the thickness of secondary wall (S2 layer) of fibre had been decreased with non-homogenous lignin distribution in antisense lines, while sense lines showed an increase in S2 layer thickness. Maule color reaction revealed that syringyl lignin distribution in the xylem elements was increased in sense and decreased in antisense lines. The immunoelectron microscopy revealed a reduction in LM 10 and LM 11 labelling in the secondary wall of antisense tobacco lines. Biochemical studies showed a radical increase in syringyl lignin in sense lines without any significant change in total lignin content, while S/G ratio decreased considerably in antisense lines. Our results suggest that CAld5H gene plays an important role in xylogenesis stages such as cambial cell division, secondary wall thickness, xylan and syringyl lignin distribution in tobacco. Therefore, CAld5H gene could be considered as a promising target for lignin modification essential for timber quality improvement in rubber.

TENSION WOOD-LIKE REACTION WOOD IN VESSEL-LESS TETRACENTRON SINENSE

The objective of this study is to clarify the anatomical characteristics and lignin distribution of reaction wood in a vessel-less angiosperm species, Tetracentron sinense Oliv. Sample disks (1 cm in thickness) were collected from three different positions of a Tetracentron sinense tree. Cell morphologies, the microfibril angle (MFA) in the S2 layer, lignin distribution, and lignin content were measured. There was neither a gelatinous (G-)layer nor an S3 layer on the upper side of inclined samples. However, the secondary wall of the normal tracheids was only weakly stained by Mäule and phloroglucinol-HCl. MFA in the S2 layer and lignin content decreased on the upper side of inclined samples. This qualifies the reaction wood of Tetracentron as “tension wood-like”. The so-called “unusual tracheids”, typical for the wood of Tetracentron, showed weaker changes in their anatomical and chemical characteristics in reaction wood than normal tracheids, indicating their special function in water transport. It is hypothesized that vessel-less angiosperms rich in syringyl units in their lignin, produce tension wood-like reaction wood on the upper side of inclined stems or branches, with lower MFA and lignin content in their normal tracheid walls, irrespective of whether a typical G-layer is formed or not.