Abstract
Reactive oxygen species (ROS) can be promoted differently, although iron is regarded as a condicio sine qua of their generation. We assessed how enzymes involved in ROS production and iron accumulation impact the interactions between Pinus sylvestris root and pathogens with different host preferences (Heterobasidion annosum sensu stricto, H. parviporum and H. abietinum). Studies with inhibitors of ROS generation showed that diphenylene iodonium (DPI) and potassium cyanide (KCN) decreased the mortality of P. sylvestris root cells when exposed to H. parviporum in the elongation zone. In the meristematic zone, inhibited production of NADPH oxidase and oxalic acid decreased mortality of host root cells challenged with H. parviporum or H. abietinum. In the meristematic zone, iron immobilization with desferoxamine (DFO), inhibited percentage of dead host cells exposed to H. annosum s.s. Scots pine inoculation with high compatible H. annosum s.s., irrespectively in the root zone, led to an accumulation of superoxides (O2 −) and a co-localisation of H2O2 with ferric or ferrous ions involved in production of the most harmful ROS – hydroxyl radicals at 4 h. After 48 h of mutual interaction between P. sylvestris and H. annousum s.s, a similar pattern as at 4 h was found in the root meristematic zone. We also showed that O2 − accumulation in the P. sylvestris – H. annosum s.s. pathosystem was not NADPH oxidase dependent. During the interaction of P. sylvestris and H. annosum s.s., colocalisation of H2O2 with Fe2+ and Fe3+ decreased by disturbing ROS production; this pattern was less apparent when H. parviporum or H. abietinum were identified as the invader. Our work implies that different mechanisms related to plant cell death can operate in both the root elongation and meristematic zone of P. sylvestris colonized with H. annosum s.s. pathosystem.
Highlights
Reactive oxygen species (ROS), mostly O2− and H2O2, are produced during plant development, but abiotic and biotic stresses can result in the rapid formation of reactive oxygen (Lamb and Dixon 1997; Dat et al 2000)
Dissimilar to the results observed for the root elongation zone, only the presence of H. annosum s.s. accelerated accumulation of O2− in the meristematic zone; more O2− was observed within 4 h after treatment with KCN, NaN3 or IA and within 48 h after treatment with ATZ (Table 2, S1)
Our previous studies revealed the patterns of H2O2, O2−, or iron ion accumulation in root cells may reflect aggressiveness of different pathogen species during the P. sylvestris defense response to H. annosum s. l. infection (Mucha et al 2012)
Summary
Reactive oxygen species (ROS), mostly O2− and H2O2, are produced during plant development, but abiotic and biotic stresses can result in the rapid formation of reactive oxygen (Lamb and Dixon 1997; Dat et al 2000). Plants, which induce ROS bursts should limit the spread of biotrophic, but not necrotrophic fungi (Shetty et al 2008). This assumption is an over-generalization, because even genotypes of Botrytis cinerea Pers., known as a necotrophic pathogen, can generate reactive oxygen bursts (Govrin and Levine 2000) might be restricted by ROS (Unger et al 2005)
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