An attractive objective in tree breeding is to reduce the content of lignin or alter its composition, in order to facilitate delignification in pulping. This has been achieved in transgenic angiosperm tree species. In this study we show for the first time that changes in lignin content and composition can be achieved in a conifer by taking a transgenic approach. Lignin content and composition have been altered in five-year-old transgenic plants of Norway spruce (Picea abies [L.] Karst) expressing the Norway spruce gene encoding cinnamoyl CoA reductase (CCR) in antisense orientation. The asCCR plants had a normal phenotype but smaller stem widths compared to the transformed control plants. The transcript abundance of the sense CCR gene was reduced up to 35% relative to the transformed control. The corresponding reduction in lignin content was up to 8%, which is at the lower limit of the 90-99% confidence intervals reported for natural variation. The contribution of H-lignin to the non-condensed fraction of lignin, as judged by thioacidolysis, was reduced up to 34%. The H-lignin content was strongly correlated with the total lignin content. Furthermore, the kappa number of small-scale Kraft pulps from one of the most down-regulated lines was reduced 3.5%. The transcript abundances of the various lignin biosynthetic genes were down-regulated indicating co-regulation of the biosynthetic pathway.

Lignin content and composition are important traits in several tree breeding programs, but very little is known about their natural variation. This study compares the lignin content in 1-year-old plants and 9-year-old trees of Norway spruce belonging to the same full-sib families. It is shown that the lignin content, according to the modified acetyl bromide method, does not vary significantly within or among the different full-sib families either as plants or as young trees. There is, however, on average 4.0% higher lignin content (31.4% versus 27.4%) and lower standard error for the trees than for the plants. The number of C9-units g y1 lignin, analyzed by thioacidolysis, ranges from 516 to 1186 mmol C9-units g y1 lignin in plants and from 716 to 953 mmol C9-units g y1 lignin in trees, with no significant differences among the families. However, the extent of change in C9-units g y1 lignin varies among the families with age. The ratio of erythro and threo stereoisomers does not vary significantly among the families. However, the ratio changes differently with age among the families similar to the C9-units g y1 lignin. Additionally, the content of p-hydroxyphenyl (H) lignin is 0.6% higher in the trees than in the plants (1.4% versus 0.8%), estimated indirectly from GC-MS data by a novel subtractive technique, indicating a higher degree of compression wood in the young trees. In conclusion, the amount and composition of lignin does not vary within or among the families at the same age. However, the amount of lignin increases with age while the change in lignin composition varies between family and age.

Background: The need to perform microarray experiments with small amounts of tissue has led to the development of several protocols for amplifying the target transcripts. The use of different amplification protocols could affect the comparability of microarray experiments.

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