Biochemical and molecular evidence for the role of class III peroxidases in the resistance of carnation (Dianthus caryophyllus L) to Fusarium oxysporum f. sp. dianthi

Abstract Rooted cuttings of two cultivars of carnation ( Dianthus caryophyllus L) with differential responses to vascular wilt caused by Fusarium oxysporum f. sp. dianthi (FOD) were inoculated with the pathogen and some parameters associated to guaiacol peroxidase activity (GPX) (E.C. 1.11.1.7) were evaluated. The resistant cultivar (L.P. Candy) showed a significant increase in GPX activity levels at 12, 24, and 48 h post-inoculation (hpi), whereas the susceptible cultivar (Tasman) exhibited only a slight increase at a longer time (96 hpi). The H 2 O 2 content in the resistant cultivar was increased at 12 and 24 hpi, with corresponding increase in GPX activity level ( α  = 0.05). However, the susceptible cultivar showed an increase in H 2 O 2 content at 12 hpi that did not correlate with GPX activity. Using zymograms, the increased GPX activity in the resistant cultivar was determined to be due to increased levels of constitutive isoforms of peroxidase. Quantification of transcriptional levels indicated that in the resistant cultivar, the mRNA level of the class III peroxidase Dcprx02 increased almost 8 fold compared with the control at 6 hpi, whereas the mRNA level in the susceptible cultivar only increased approximately 2 fold at 12 hpi. The increased levels of H 2 O 2 correlated with the increased levels of Dcprx02 transcription. Differences in the temporal regulation of the variables assessed during infection support the idea that the generation of reactive oxygen species (ROS) and subsequent regulation mediated by the action of antioxidant enzymes such as GPX are relevant to plant resistance to the vascular wilt causal agent.