Effect of Fumonisin B1 toxin on defence systems in susceptible and resistant maize seedlings

At the three-leaf stage, sterile seedlings of resistant (CO433) and susceptible (CO389) maize lines was spiked with fumonisin B1 (FB1) (dissolved in PBS, pH =7.4, at the final concentration of 1mg/mL) in the part of the stem between the collar and the insertion of the first leaf. At various times, the FB1 content was determined by the use of HPLC/FLD previously derivatized with an o-phthaldeyde (OPA). The stem was ground with liquid nitrogen and extracted with a solution methanol/water (70:30, v/v). Recovery was 106% (RSD < 8%). The concentration of FB1 after 3 hours (88%, RSD 12%) and 48 hours (92%, RSD 7%) after spiking showed that no translocation in seedling maize occurred. To evaluate if the defence systems were alerted, the leaves were used to monitor the ascorbate-glutathione cycle, phenolics and enzymes protective from oxidative stress (catalase, superoxide dismutase and cytosolic peroxidases) at 3 and 48 hours post-spiking. The study was also extended to the analysis of total antioxidants, hydrogen peroxide and malondialdehyde contents to evaluate the oxidation level after FB1 treatment. Defense response promptly appeared activated in leaves of resistant line; particularly, after 3h, ascorbate, ascorbate peroxidase, SOD were augmented, underlining a higher fitness in the counteracting the phytotoxic action of FB1. In contrast, in the susceptible line, catalase, phenolics and ascorbate increased at longer time, conferring a lower readiness to the FB1 treatment. Same trend in total antioxidants, cytosolic peroxidases and other components analyzed was observed in both CO433 and CO389 after spiking. FB1, although did not cause seedlings suffering, induced metabolic perturbations. These data are useful for further investigation on molecular mechanisms that are to the basis of the FB1 and others mycotoxins contamination in maize, in order to improve resistance to fungal pathogens.