THE ROLE OF LACCASE IN LIGNIFICATION

The enzymatic mechanism of monolignol polymerization in lignin biosynt hesis is not known, although it has been the subject of significant in terest for more than 60 years. Peroxidase had been considered to be th e exclusive plant enzyme involved in the oxidative polymerization of l ignin precursors. Recently, laccase and laccase-like oxidase activitie s have been associated with lignification. Laccase is bound to lignify ing plant cell walls and can polymerize lignin precursors in vitro. St rong circumstantial evidence from different species implicates this en zyme in the polymerization of lignin precursors. Lignin has a complex structure and it has been difficult to analyze the heterogeneity of li gnin by chemical and physical techniques. If lignin precursors are pol ymerized by enzymes that differ in their catalytic properties, then li gnin heterogeneity could be produced by differential expression of mul tiple enzymes during plant development. When laccase genes are correct ly identified, these ideas can be tested in genetic experiments where gain or loss of function can be predicted by the presence or absence o f the functional gene.