RECENT ADVANCES IN UNDERSTANDING LIGNIN BIOSYNTHESIS.

After a long period of little change, the basic concepts of lignin biosynthesis have been challenged by new results from genetic modification of lignin content and composition. New techniques for making directed genetic changes in plants, as well as improvements in the analytical techniques used to determine lignin content and composition in plant cell walls, have been used in experimental tests of the accepted lignin biosynthetic pathway. The lignins obtained from genetically modified plants have shown unexpected properties, and these findings have extended the known range of variation in lignin content and composition. These results argue that the accepted lignin biosynthetic pathway is either incomplete or incorrect, or both; and also suggest that plants may have a high level of metabolic plasticity in the formation of lignins. If this is so, the properties of novel lignins could be of significant scientific and practical interest.