Fig. 1. The main pathway involved in monolignol biosynthesis in biomass cell wall. The three monolignol precursors shown with a gray background resulted from the downregulation of CAD gene. PAL, phenylalanine ammonia lyase; C4H, cinnamate 4-hydroxylase; 4CL, 4-coumaric acid-CoA ligase; HCT, hydroxycinnamoyl-CoA shikimate hydroxycinnamoyl transferase; pC3H, p-coumarate 3-hydroxylase; CCR, cinnamoyl-CoA reductase; CCOMT, caffeoyl-CoA O-methyltransferase; F5H, ferulate 5-hydroxylase; COMT, caffeic acid O-methyltransferase; CAD, cinnamyl alcohol dehydrogenase.
Fig. 3. Gas chromatograms obtained from the pyrolysis of WT and CAD mutant at 500 ℃.
Fig. 4. Yields of lignin derivatives based on number of carbons in side chain obtained at 400 ℃ (left) and 500 ℃ (right).
Fig. 5. Yields of lignin derivatives based on lignin subunits (H, G and S units) obtained at 400 ℃ (left) and 500 ℃ (right).
Fig. 6. Optimized geometry of (A) β-O-4’ (guaiacylglycerol-β-guaiacyl ether) structure found in WT and (B) 8-O-4’ dimer (guaiacylacrylaldehyde-β-guaiacyl ether) found in CAD downregulated biomass.
Fig. 7. Electrophilicity index of β-O-4’ structure found in WT and 8-O-4’ dimer found in CAD downregulated biomass.
Fig. 2. (A) Main structures of typical lignin subunits and (B) new structures present in the lignin of CAD downregulated biomass (Zhao et al., 2013).
Table 1. The yield of pyrolysis products from WT and CAD mutant lignin at 400 and 500 ℃ (μg/mg lignin).
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