Average effect of a mutation in lignin biosynthesis in loblolly pine

Cinnamyl alcohol dehydrogenase (CAD, E.C. 1.1.1.195) is a monolignol biosyn thetic enzyme that catalyzes the final step of lignin subunit biosynthesis in higher plants. Recently, a mutant allele of the cad gene, cad-n1, encodi ng for the CAD enzyme, was discovered in loblolly pine. By reducing the exp ression of the cad gene, this mutant has a decreased lignin content and maj or changes in the lignin composition in wood. In this study, we found that the substitution of a wild-type allele by cad-nl was associated with a sign ificant effect on 2nd-year shoot elongation in a half-sib family of lobloll y pine (designated family 7-1037). The average effect of cad-nl appeared to increase with tree growth and was greater for stem radial growth than heig ht growth. An increase of 14.1% in de-barked volume in year 4 was associate d with cad-nl. Go-segregation analysis indicated that the cad locus itself might represent a gene that governs stem growth in pine. The significance o f the mutation cad-nl for tree growth and wood processing is discussed.