Involvement of lipoxygenases in the response of peanut seeds to infection by aflatoxigenic fungies

MÜLLER, VIRGINIA; GIECO, JORGE; ASIS, RAMÓN

Conferencia; Mycored Argentina ISM 2011 Conference; 2011

Background:Aspergillus flavus and parasiticus are aflatoxigenics fungi that infect peanut seeds in the field and the post harvest. One of the strategies to decrease the risk of peanut aflatoxin contamination is the use of genotypes with resistance to Aspergillus infection. One of the defense mechanisms is the lipoxygenase (LOX) pathway, where the LOX is the central enzyme to generate a cascade of bioactive products. Previous studies in our group revealed the presence of fatty-acids with antifungal activity in infected peanut. Aims:To study the lipoxygenase pathway during the infection with A. parasiticus and aflatoxins contamination in peanut seeds. Material and Methods: In order to evaluate metabolic processes of LOX pathway, the kinetics of central enzyme LOX in the infection was studied. For this study, a susceptible and a resistant to aflatoxins contamination genotype was used. Surface disinfested and rehydrated peanut seeds were infected with a spore solution of 1x104 esp./ml. and incubated in moist chambers at 28˚ C for: 5hs., 10hs., 20hs., 27hs., 48hs. and 72hs. LOX activity was measured by spectrophotometric analysis at 234nm using linoleic acid as a substrate. Acidity of oils was determinated by titration with sodium hydroxide. Hydroperoxides (HODE) were measured by SP-HPLC previous reduction of hydroperoxides to hydroxyacids. Aflatoxins were extracted from a ground sample with methanol/water (80:20v/v), and after cleanup step on florosil SPE columns, aflatoxins were quantified by HPLC equipped with a C18 column and a fuorescence detector. Results and discussion: A negative association between LOX activity, A. parasiticus infectionand aflatoxins contamination was found. The comparison of LOX activity between genotypes showed significant differences at 20hs post inoculation where the LOX activity in the resistant cultivar was five times higher. The analysis of HODE composition (13HODE y 9HODE) by HPLC showed the LOX isoenzymes present in seeds during the infection. The significant differences of the LOX products ratio were observed in the first 24 hs of infection. These results suggest the existence of differents responses of LOX isoenzymes and LOX activities in the genotypes. During the infection, the free fatty acids levels correlated positively with the increase of fungal mycelium and lipolytic activity. These results evidence the participation of LOX pathway in response to Aspergillus infection and their association with peanut seeds resistance to Aspergillus infection and aflatoxins contamination.