Dependence on Ethylene of the Induction of Peroxidase and Lipoxygenase Activity in Rice Leaf Infected with Blast Fungus

Abstract

Rice leaf POX (EC 1.11.1.7) and LOX (EC 1.13.11.12) activities were induced by press-injured application of ETP, an ethylene generating chemical, ACC and Glu. A higher concentration of Glu was required to induce rice leaf POX when compared with the induction of LOX and the previously reported case of PAL. Both the POX and LOX activities were induced by press-injured inoculation with incompatible or compatible blast fungus conidia, or by press-injured application of its RIF. The induction of POX by press-injured inoculation of incompatible conidia, compatible conidia or RIF was inhibited by a preapplication of TR, AOA, CY or ABA, while the induction of LOX was similarly inhibited by the former three, but not at all, or only weakly inhibited by ABA. The activity itself of induced POX or LOX was not inhibited by the inhibitors used in this experiment. The enzyme induction spectra either by the incompatible or compatible combination in terms of tm (the time to the maximum rate of induction after inoculation) showed good orderliness (O^-₂ FES<PAL< LOX<POX) with the relaxation in compatible combination. A higher outbreak of rice blast was observed when rice seedlings were pretreated with TR, AOA or ABA 4 hr before the spray inoculation.