John MacKay, Tim Presnell, Hasan Jameel, Hidetaka Taneda, David O'Malley, Ronald Sederoff
Modified Lignin and Delignification with a CAD-Deficient Loblolly Pine
Summary
Lignin composition and lignin removal were investigated in loblolly pines (Pinus taeda L.) deficient in
the monolignol biosynthesis enzyme, cinnamyl alcohol dehydrogenase (CAD). The CAD-deficient pines
were homozygous for the cad-n1 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 link 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 CAD-deficient tree had substantially higher incorporation of
aldehyde subunits. The CAD-deficient wood was delignified more extensively than the wild type in
soda pulping but not in kraft conditions. More extensive lignin removal, both in mild alkali treatment
and in soda pulping, indicate that suppression of CAD in softwood trees may hold promise to produce
woods well suited for “milder” pulping conditions that consume less chemicals and generate less waste.
Holzforschung, Walter de Gruyter
Print ISSN: 0018-3830
Volume: 53, 07/1999
Pages: 403 - 410
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