EFFECTS OF GENETIC MANIPULATION (HCT AND C3H DOWN-REGULATION) ON MOLECULAR CHARACTERISTICS OF LIGNIN AND ITS BIOCONVERSION TO FERMENTABLE SUGARS

摘要

The molecular characteristics of lignin from hydroxycinnamoyl transferase (HCT) and p-coumarate 3-hydroxylase (C3H) down-regulated 84 k poplar (after four years of growth in field) have not been investigated in detail. In the present study, modified enzymatic mild acid lignin (EMAL) samples were extracted with high yield and purity. NMR characterization of the lignins demonstrated that all the EMALs presented typical and common substructures (beta-O-4',, beta-beta' and (beta-5'), although the down-regulated poplar lignin had a high content of beta-O-4' linkages. Interestingly, the total OCH3 contents in the HCT-EMAL and C3H-EMAL were found to be decreased, while the corresponding S/G ratios were increased. In addition, it was observed that the p-hydroxybenzoate (PB) content was increased in the lignin from HCT and C3H down-regulated poplar, respectively. Moreover, HCT and C3H down-regulation slightly enhanced the enzymatic hydrolysis of 84 k feedstock to 33% (40-60 mesh) as compared to 26% of CK, while the enzymatic hydrolysis of down-regulated poplar (ball-milled) were obviously improved to 78% as compared to 61% of CK poplar. These findings are vital in assessing and evaluating the effects of down-regulated HCT and C3H genes on the molecular characteristics of lignin and the digestibility of HCT and C3H down-regulated poplar in the fuel production.