Structure and Monomer Ratio of Lignin in C3H and HCT RNAi Transgenic Poplar Saplings

Abstract

AbstractWild type poplar hybrid (Populus alba × P. glandulosa cv‘84k′), p‐coumaroyl shikimate 3′‐hydroxylase (C3H) downregulated transgenic poplar and hydroxycinnamoyl CoA: shikimate hydroxycinnamoyl transferase (HCT) downregulated transgenic poplar were used as experimental materials. The techniques of two‐dimensional heteronuclear single‐quantum coherence nuclear magnetic resonance (2D‐HSQC‐NMR) spectroscopy and pyrolysis coupled to gas chromatography‐mass spectrometry (Py‐GC/MS) were used for the analysis and comparison of the lignin structure and monomer ratio between the wild type poplar hybrid and transgenic plants. The results of these analyses showed that the lignin of all poplar samples contained β‐O‐4′ aryl ether linkages and their derivative substructures, resinol substructures, spirodienone substructures, phenylcoumarane substructures, p‐hydroxycinnamyl alcohol end groups, syringyl units, p‐hydroxyphenyl units, guaiacyl units, p‐hydroxybenzoate substructures, and ferulate. Downregulation of C3H and HCT in double transgenic poplar reduced the β‐O‐4′ relative content of lignin in poplar. The S unit, H unit, and S/G ratio in the C3H‐downregulated transgenic poplar were increased, while its G unit was decreased. The S unit and S/G ratio in HCT‐downregulated transgenic poplar were decreased while its G unit was increased. The C3H‐downregulated transgenic poplar was a superior material for biomass energy, pulping, and papermaking than the HCT‐downregulated transgenic poplar.