EXTRACELLULAR LACCASES AND PEROXIDASES FROM SYCAMORE MAPLE (ACER-PSEUDOPLATANUS) CELL-SUSPENSION CULTURES - REACTIONS WITH MONOLIGNOLS AND LIGNIN MODEL COMPOUNDS
R. Sterjiades et al., EXTRACELLULAR LACCASES AND PEROXIDASES FROM SYCAMORE MAPLE (ACER-PSEUDOPLATANUS) CELL-SUSPENSION CULTURES - REACTIONS WITH MONOLIGNOLS AND LIGNIN MODEL COMPOUNDS, Planta, 190(1), 1993, pp. 75-87
We have investigated the abilities of extracellular enzymes from dark-
grown cell-suspension cultures of sycamore maple (Acer pseudoplatanus
L.) to oxidize monolignols, the precursors for lignin biosynthesis in
plants, as well as a variety of other lignin-related compounds. Laccas
e and peroxidase both exist as a multiplicity of isoenzymes in filtrat
es of spent culture medium, but their abilities to produce water-insol
uble, dehydrogenation polymers (DHPs) from the monolignols (in the pre
sence of hydrogen peroxide for the peroxidase reaction) appear identic
al whether or not the enzymes are purified from the concentrated filtr
ates or left in a crude mixture. The patterns of bonds formed in these
DHPs are identical to those found in DHPs synthesized using horseradi
sh peroxidase or fungal laccase, and many of these bonds are found in
the natural lignins extracted from different plant sources. On the oth
er hand, sycamore maple laccase is very much less active on phenolic s
ubstrates containing multiple aromatic rings than is sycamore maple pe
roxidase. We suggst that whereas laccase may function during the early
stages of lignification to polymerize monolignols into oligo-lignols,
cell-wall peroxidases may function when H2O2 is produced during the l
ater stages of xylem cell development or in response to environmental
stresses.