Role of peroxidase in cotton resistance to bacterial blight

Abstract

Peroxidase activity in blight resistant cotton cotyledons syringe-injected with 10 8 viable cells of Xantomonas malvacearum (E.F. Sm.) Dows. increased aboout 2-fold over zero-time controls 12 h after inoculation. No increase in peroxidase activity was observed in extracts from blight resistant cotyledons injected with heat-killed cells (120°C at a pressure of 1.05 kg × cm −2 for 10 min) No increase in peroxidase activity was observed in extracts from blight susceptible cotyledons that were inoculated with either viable or heat-killed bacterial cells. Bacterial numbers in both resistant and susceptible cotyledons increased about 3-fold during the first 3 h after inoculation. Bacteria multiplied another 6-fold in susceptible cotyledons during the next 9 h but decreased about 25-fold in the resistant cotyledons. Soluble and wall-bound peroxidase fractions isolated from the blight resistant cotyledons (when exposed to catechin and hydrogen peroxide) produced a product(s) bactericidal to X. malvacearum. These results suggest that oxidation of catechin by peroxidase may be a factor in restricting growth of the bacterial pathogen in blight resistant cotton.