Submitted to: Molecular Plant-Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/5/2007
Publication Date: 4/1/2007
Citation: Magbanua, Z.V., Demoraes, C.M., Brooks, T.D., Williams, W.P., Luthe, D.S. 2007. Is catalase activity one of the factors associated with maize resistance to Aspergillus flavus. Molecular Plant-Microbe Interactions. 20:697-706. Interpretive Summary: Contamination of corn with aflatoxin, a naturally occurring toxin produced by the fungus Aspergillus flavus, limits the profitability of corn production in the southern United States. Genetic resistance to A. flavus infection and/or aflatoxin accumulation in corn kernels is generally considered to have the greatest potential for effectively reducing losses to aflatoxin contamination. ARS scientists have developed and released corn germplasm lines that exhibit resistance to A. flavus infection and/or aflatoxin contamination. In this investigation, catalase activity was shown to be higher in immature embryos in developing seed of aflatoxin-resistant germplasm lines than in embryos in the seed of susceptible lines after inoculation with A. flavus. The resistant lines also had lower levels of peroxidase and salicylic acid than susceptible lines. Determining chemical differences between aflatoxin-resistant and susceptible corn germplasm lines in their responses to fungal infection will enhance efforts to breed and commercialize aflatoxin-resistant corn hybrids. Such hybrids will provide the key to effectively reducing aflatoxin contamination.
Technical Abstract: Catalase activity was measured in various cob tissues during maize ear development because of its role in maintaining reactive oxygen homeostasis during biotic and abiotic stress. Catalase activity was determined in immature and mature embryos, pericarp, and rachis tissues of maize lines that are resistant and susceptible to Aspergillus flavus infection. The effect of fungal inoculation on catalase activity was also measured. Over two years of field experimentation, a positive correlation was observed between resistance and the level of catalase activity in immature embryos, which was significantly higher in resistant lines (P<0.0001). Furthermore, catalase activity in resistant lines was significantly higher in immature embryos from inoculated ears (P=0.0199). A significant correlation was not observed between resistance and catalase activity in other ear tissues. Levels of catalase substrate H2O2 and salicylic acid in the embryo were also determined. The resistant lines showed lower levels of H2O2 (P<0.0001) and higher levels of salicylic acid (P<0.0001) compared to the susceptible lines. Unlike many plant-pathogen interactions, it appears that lowering H2O2 levels helps prevent A. flavus infection and subsequent aflatoxin accumulation.