Abstract
This research focused on the cell wall structure and its mechanical properties of down-regulated Coumaroyl shikimate 3-hydroxylase (C3H) transgenic poplar and down-regulated hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT) transgenic poplar (Populus alba × P. glandulosa cv ‘84 k’). The wood samples with respect to microstructure, the longitudinal elastic modulus (MOE) and hardness of wood fiber secondary cell wall were investigated. The results show that the lignin contents in the two transgenic poplar woods were lower than non-modified wood. The C3H transgenic poplar and HCT transgenic poplar have more than 18.5% and 16.1% cellulose crystalline regions than non-modified poplar respectively. The diameter of the fiber cell and the vessel element of transgenic poplars are smaller. Double radial vessel cell wall thicknesses of both transgenic poplars were smaller than non-modified poplar. Cell wall ratios for the transgenic poplar were higher than non-modified poplar and cell wall density was significantly lower in both C3H and HCT transgenic poplar. The cell wall MOEs of C3H and HCT transgenic poplar was 5.8% and 7.0% higher than non-modified poplar. HCT can be more effective than C3H to modify the trees by considerably increasing mechanical properties of the cell wall.
Highlights
The genetic engineering technology was used to regulate the biosynthesis process of lignin in trees
The results showed that the lignin content of both transgenic poplars lowered markedly, the lignin content of Coumaroyl shikimate 3-hydroxylase (C3H) transgenic poplar and hydroxycinnamoyl transferase (HCT) gene was decreased by 29.9% and 20.3% respectively
The lignin contents in both C3H and HCT transgenic poplar wood were significantly lower than lignin conents of non-modified wood
Summary
The genetic engineering technology was used to regulate the biosynthesis process of lignin in trees. This technology can reduce the lignin content or change its structure and composition[14]. C4H, 4CL, C3H, CAD, CCR, COMT, CCoAOMT and other genes can reduce significantly lignin content, especially C3H, C4H and 4CL5–11. It has been found that the down-regulated CCR gene can increase the ratio of fiber length to width of transgenic poplar (Populus × euramericana)[24]. Down-regulated CCoAOMT gene can increase fiber width, ratio of cell wall to lumen, cell wall thickness and long fiber (greater than 0.61 mm) distribution frequency and reduce cell lumen diameter[22]. Nano indentation (NI) tests were performed to measure the longitudinal elastic modulus and the hardness of wood fiber secondary cell walls
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