CHARACTERIZATION OF VASCULAR LIGNIFICATION IN ARABIDOPSIS-THALIANA

The developmental timing of lignin biosynthesis and the nature of the polymer have been studied in Arabidopsis thaliana using biochemical and histological techniques. Embryos and developing seedlings were stained with basic fuchsin, and the internal vascular strands were imaged by the optical serial sectioning capability of confocal laser scanning microscopy. Lignin could not be detected in seedlings until approximately 36 h after germination. As the radicle, hypocotyl, and cotyledon expanded, lignification proceeded as a temporally coordinated event closely linked to appearance of spiral or annular thickenings in the developing vasculature. Although A. thaliana does not undergo secondary growth, the plants were extensively lignified by the bolting stage. Chemical analysis demonstrated that Arabidopsis lignin contains primarily guaiacyl units, accompanied by lesser amounts of syringyl structures.