ORIGINAL ARTICLE

Hydrogen Peroxide and Phenylalanine Ammonia-lyase as Signalling Molecules in Barley Leaves Challenged with Cochliobolus sativus

Hydrogen peroxide (H₂O₂) and phenylalanine ammonia-lyase (PAL) have been reported as important signaling molecules during plant resistance against many fungal pathogens. In this study, the relative contributions of H₂O₂ and PAL were investigated at early time periods of barley infection with Cochliobolus sativus, the causal agent of spot blotch disease. H₂O₂ activity was observed in leaf tissues 24 hours post inoculation (hpi) and was accompanied with an increase in PAL expression in resistant and susceptible genotypes. However, the resistant genotype ‘Banteng’ contained higher levels of H₂O₂ and PAL, as compared with the susceptible one ‘WI 2291’. Results demonstrated that the cooperative function of H₂O₂ and PAL in barley responses to C. sativus appeared to be dependent on the plant genotype, and it is hypothesized that the peak of activity of PAL at 48h and 72 h, and the rapid increase in H₂O₂ 24 h in resistant and susceptible genotypes are considered general defense responses.