Diferulate and lignin formation is related to biochemical differences of wall-bound peroxidases

Purified cell walls from oat coleoptiles contain ionically and covalently bound peroxidase activity, which correspond to 0.6% of the total peroxidase activity in the coleoptile. Ionically wall-bound peroxidases showed a 2-3-fold higher efficacy than peroxidases in the covalent Fraction, in the use of H2O2 and phenolic substrates that are precursors of diferulate bridges and lignin. The NADH oxidase activity in both fractions was effectively enhanced by p-coumaric acid and the ionic fraction showed a higher efficacy over the covalent one for NADH utilization in the presence of this phenol. Moreover, the isoelectrofocusing pattern revealed marked differences in isoform composition for ionically and covalently bound wall peroxidases. A cationic group of isoperoxidases (pI similar to 9.6) was present only in the ionic fraction while the covalent fraction was enriched with anionic forms (pI similar to 4.0-6.5). In excised coleoptiles incubated for 24 h, the ionically wall-bound peroxidase activity increased by 50% over covalently bound activity for 4 h of incubation. The increase of peroxidase activity preceded the accumulation of diferulic acid and lignin in oat cell walls. Thus, the evidence here reported suggest a possible functional difference of peroxidase wall fractions studied related to diferulate and lignin synthesis in oat coleoptiles. (C) 1998 Elsevier Science Ltd. All rights reserved.