Role of wall peroxidases in oat growth inhibition by DIMBOA

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA). an effective growth- inhibitor of oat coleoptiles, enhanced 1524 and 246 limes the rate of NADH oxidation by ionically and covalently bound oat cell wall peroxidases. a re action that generates H2O2. This effect was similar to that of p-coumaric a cid, while ferulic add was a poor activator of this reaction. Coniferyl alc ohol did not activate NADH oxidation. DIMBOA was poorly utilized by ionic o r covalent oat wall peroxidases in the presence of H2O2. With horseradish p eroxidase, DIMBOA efficiently promoted compound III breakdown with a decomp osition rate constant of 4.88 x 10(-2) s(-1). This effect was 14 times high er than that obtained with p-coumaric acid that rave a decomposition rate c onstant of. 0.35 x 10(-2) s(-1). The diferulate and lignin levels in the ce ll walls from oat coleoptiles increased by 56 and 30%, respectively. upon D IMBOA treatment. The effect of DIMBOA on oar wall peroxidases would thus co ntribute to its growth inhibitory effect by promoting H2O2 synthesis and ph enol coupling at the cell wall level. (C) 1999 Elsevier Science Ltd. Aii ri ghts reserved.