Modified lignin and delignification with a CAD-deficient loblolly pine

Lignin composition and lignin removal were investigated in loblolly pines ( Pinus taeda L.) deficient in the monolignol biosynthesis enzyme, cinnamyl a lcohol dehydrogenase (CAD). The CAD-deficient pines were homozygous for the cud-nl allele, a mutant form of the gene encoding CAD. We show that lignin from CAD-deficient seedlings is more easily removed by mild alkali at room temperature. The nature of the phenolics recovered from this treatment lin k the increased lignin solubility to a build up of aromatic aldehyde lignin subunits. We carried out a retrospective genetic analysis to identify a 12 year-old CAD-deficient tree from which we isolated Milled Wood Lignin (MWL ) and obtained wood chips for pulping studies. The UV absorption spectra of MWL and the effect of sodium borohydride reduction of MWL showed that the GAD-deficient tree had substantially higher incorporation of aldehyde subun its. The CAD-deficient wood was delignified more extensively than the wild type in soda pulping but not in kraft conditions. More extensive lignin rem oval, both in mild alkali treatment and in soda pulping, indicate that supp ression of CAD in softwood trees may hold promise to produce woods well sui ted for "milder" pulping conditions that consume less chemicals and generat e less waste.