1 Lignin biosynthesis studies in plant tissue cultures

Lignin, a phenolic polymer abundant in cell walls of certain cell types, has given challenges to scientists that study its structure or biosynthesis. In plants lignified tissues are distributed between other, non-lignified tissues. Characterisation of native lignin in the cell wall has been difficult due to the highly cross-linked nature of the wall components. Model systems, like plant tissue cultures with tracheary element differentiation or extracellular lignin formation, have provided useful information related to lignin structure and several aspects of lignin formation. For example, many enzyme activities in phenylpropanoid pathway have been first identified in tissue cultures. This review focuses on studies where the use of plant tissue cultures has been advantageous in structural and biosynthesis studies of lignin, and discusses the validity of tissue cultures as models for lignin biosynthesis.