This induction of DON was confirmed in an in vivo experiment in which flowering wheat plants were infected with F. graminearum and subjected to a sub lethal

dose of prothioconazole + fluoxastrobin. Previous work on F. culmorum demonstrated no or a negative effect of several strobilurins and triazoles on DON production [24] so the observed phenomenon of an increased DON production by F. graminearum induced by sub lethal concentrations of triazole fungicides might be a strain- or species-specific phenomenon. It is tempting to speculate whether this accumulation of DON is the consequence of the preceding accumulation of H2O2 as such being the first link in a signalling cascade activated upon sub lethal triazole treatment. Although this key role Selleckchem ZIETDFMK of H2O2 is not unambiguously demonstrated in the present study, the amount of evidence is compelling: H2O2 precedes accumulation of DON, combined application of catalase (eliminating H2O2 from the medium) inhibited DON accumulation. In addition, the application led to a reduced activity of the triazole fungicide. Application of H2O2 to F. graminearum cultures led to a reduced germination

and prompt induction of DON biosynthesis 4 h after H2O2 application. This additional experiment proves that H2O2 accumulation is necessary and sufficient to initiate DON production. The activation of the DON biosynthesis machinery by H2O2 is in concordance with previous observations C59 wnt price by the group of Barreau [17, 19, 20] who demonstrated that exogenously applied H2O2 by

repeated single or pulse-feeding resulted in accumulation of DON. However, these authors only monitored increases in DON at late time points such as 10 to 30 days after H2O2 application whereas we AZD1480 molecular weight observe a clear prompt activation of DON production within hours. From a physiological point Cyclooxygenase (COX) of view the effect of H2O2 during the initial germination events is logic and in line with the physiology of an in field F. graminearum infection: H2O2 is one of the key regulators in the plant defense system upon pathogen attack [30]. Therefore, this molecule is encountered frequently and at early time points by the pathogen in the interaction with its host. Previous work by the group of John Manners demonstrated beautifully that DON itself can induce hypersensitive cell death and H2O2 during infection [5] and as such underpinning the interaction between both molecules. Astonishingly, very low concentrations of H2O2 promoted conidia germination rate where a reduction was expected. We hypothesize that during germination events, very small amounts of H2O2 are beneficial and necessary in the primordial germination- and hyphal extension events. It is known that H2O2 is necessary in de novo synthesis of cell wall and membrane components during germination and hyphal extension.