A LACCASE-LIKE PHENOLOXIDASE IS CORRELATED WITH LIGNIN BIOSYNTHESIS IN ZINNIA-ELEGANS STEM TISSUES

Stem tissues from different internodes of 4-6 week-old Zinnia elegans cv. Envy plants were sectioned and stained with chromogenic substrates previously used in studies of laccases (p-diphenol:O-2 oxidoreductase s) isolated from tree tissues. The pattern of color development found when stem sections were stained in the presence and absence of H2O2 su ggested that p-diphenol:O-2 oxidoreductase activity was tightly correl ated spatially and temporally with the lignification of secondary cell walls in developing primary xylem. The correlation between this lacca se-like phenoloxidase activity and lignification appeared tighter than that between lignification and peroxidases stained using the same sub strates. Zymogram analysis of the phenoloxidase activities catalyzed b y enzymes that were not boiled prior to separation by SDS-PAGE suggest ed that a single enzyme was predominantly responsible for the laccase- like phenoloxidase activity in Zinnia stems. Some of this enzyme was r eleased from cell wall residue by washing with high ionic strength buf fer; however, substantial amounts of the enzyme could only be recovere d after treatment of the residue with cell wall-degrading enzymes. Thi s phenoloxidase appears to share significant characteristics with the coniferyl alcohol oxidase isolated from developing secondary xylem in pines, which suggests that such enzymes may be widespread in vascular plants.