Lignin structure in a mutant pine deficient in cinnamyl alcohol dehydrogenase

Cinnamyl alcohol dehydrogenase (CAD) activity is deficient in loblolly pine (Pinus taeda L.) harboring a mutated allele of the cad gene (cad-n1). We c ompared lignin structure of CAD-deficient; and wildtype pines, both types s egregating within full-sib families obtained by controlled crosses. The typ e and frequency of lignin building units and distribution of interunit bead s were determined from the GC-MS analysis of thioacidolysis monomers and di mers. While the lignin content was only slightly reduced, the lignin struct ure was dramatically modified by the mutation in both mature and juvenile t rees. Lignins from CAD-deficient pine displayed unusually high levels of co niferaldehyde and dihydroconiferyl alcohol. In addition, biphenyl and biphe nyl ether bonds were in large excess in these abnormal lignins. These resul ts suggest that the CAD-deficient pines efficiently compensate for the shor tage in normal lignin precursors by utilizing nontraditional wall phenolics to construct unusual lignins particularly enriched in resistant interunit bonds.