Effect of lignin content and structure on the anatomical, physical and mechanical properties of genetically engineered aspen trees.

Abstract

The effect of lignin genetic engineering on various wood properties were investigated for wild-type and transgenic quaking aspen (Populus tremuloides Michx.) groups with reduced lignin content, increased syringyl to guaiacyl (S/G) ratio, and both reduced lignin content and increased S/G ratio in four studies. In the first study, diameter growth and cell morphology of one-year-old transgenic aspen were assessed using quantitative wood anatomy and fiber quality analysis techniques. The genetic group with reduced lignin content had similar radial growth and quantitative anatomical properties, but the genetic group with increased S/G ratio had lower diameter growth and different vessel structure compared to the wild-type. The combined effect of lignin content and structural changes was more complex and gave inconsistent results. In the second study, dynamic modulus of elasticity (MOE) using a nondestructive acoustic technique and static MOE using micromechanical testing method were investigated for 2.5-year-old transgenic aspen. Results showed that all of the transgenics had lower MOE than the wild-type. In the third study, a dynamic mechanical analyzer (DMA) in static bending mode was used to determine the elastic modulus in water and ethylene glycol for 2.5-year-old transgenic aspen. Dynamic mechanical analyzer MOE values were compared to MOE values determined by nondestructive acoustic technique and micromechanical testing. All of the measured elastic moduli showed a similar trend of lower MOE for transgenics compared to the wild-type. In the fourth study, the in situ lignin glass transition of one-year-old transgenic aspen was investigated using a dynamic mechanical analyzer and a rheometer. Results suggested that an increase in the S/G ratio does not affect the glass transition temperature, but a reduction in lignin content decreased the softening temperature of transgenic wood. This research revealed that a reduction in lignin content had a more severe effect on wood properties than an increase in S/G ratio. However, diameter growth of transgenic trees with increased S/G ratio was lower. The combined effect of reduced lignin content and increased S/G ratio was inconsistent and needs further investigation.