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

Purified cell walls from oat coleoptiles contain ionically and covalently b ound peroxidase activity, which correspond to 0.6% of the total peroxidase activity in the coleoptile. Ionically wall-bound peroxidases showed a 2-3-f old higher efficacy than peroxidases in the covalent Fraction, in the use o f H2O2 and phenolic substrates that are precursors of diferulate bridges an d lignin. The NADH oxidase activity in both fractions was effectively enhan ced 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. More over, the isoelectrofocusing pattern revealed marked differences in isoform composition for ionically and covalently bound wall peroxidases. A cationi c 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 s imilar to 4.0-6.5). In excised coleoptiles incubated for 24 h, the ionicall y wall-bound peroxidase activity increased by 50% over covalently bound act ivity for 4 h of incubation. The increase of peroxidase activity preceded t he accumulation of diferulic acid and lignin in oat cell walls. Thus, the e vidence here reported suggest a possible functional difference of peroxidas e wall fractions studied related to diferulate and lignin synthesis in oat coleoptiles. (C) 1998 Elsevier Science Ltd. All rights reserved.