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Is Catalase Activity One of the Factors Associated with Maize Resistance to Aspergillus flavus?

¹Department of Plant and Soil Sciences, Box 9555, Mississippi State University, MS 39762, U.S.A.; ²Department of Entomology, 535 ASI, Pennsylvania State University, University Park, PA 16802, U.S.A.; ³USDA, ARS, Corn Host Plant Resistance Research Unit, Box 5367, Mississippi State, MS 39762, U.S.A.; ⁴Department of Crop and Soil Sciences, 116 ASI, Pennsylvania State University, University Park, PA 16802, U.S.A.

Plant responses to biotic and abiotic stresses are usually accompanied by the release of reactive oxygen species including hydrogen peroxide. Hydrogen peroxide plays a direct role in defense and is involved in many signal transduction pathways that lead to the proliferation of other defenses. Because catalase helps to maintain reactive oxygen homeostasis during biotic and abiotic stress, its activity was measured in various cob tissues during maize ear development. 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 correlation was observed between resistance and the level of catalase-specific activity in immature embryos, which was significantly higher in resistant lines (P < 0.0001). Furthermore, catalase activity in the resistant lines was significantly higher in immature embryos from inoculated ears (P = 0.0199). No correlation was observed between resistance and catalase activity in other ear tissues. Levels of hydrogen peroxide, the catalase substrate, 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) as compared with the susceptible lines. Catalase 3 was sequenced from the aflatoxin-resistant (Mp313E) and -susceptible (SC212m) inbreds. The predicted amino acid sequence indicated that there was a 20-aa deletion in the resistant inbred that might affect enzymatic activity. Unlike many plant-pathogen interactions, it appears that lowering H₂O₂ levels helps to prevent A. flavus infection and subsequent aflatoxin accumulation.

Additional keywords: oxidative stress.