Enhanced maize (Zea mays L.) pericarp browning: Associations with insect resistance and involvement of oxidizing enzymes

The kernel pericarp of a maize (Zea mays L.) inbred, Mp313E, that browns rapidly at milk stage when damaged and that is resistant toAspergillus flavus Link and the dusky sap beetleCarpophilus lugubris Murray compared to a susceptible inbred, SC212M, was examined for differing oxidizing enzymes (peroxidases) and their substrate specificity. Additional pericarp enzymes were constitutively produced by the Mp313E inbred compared to the SC212M inbred, as indicated by gel electrophoresis and isoelectric focusing. These enzymes oxidized relevent pericarp substrates such as ferulic acid. Similar results were seen with two varieties of maize containing theCh mutant gene, which brown upon senescence in that enhanced oxidation of ferulic acid was seen in homogenates of browned pericarp compared to that which was cold-shocked and did not brown. Corn powder that was browned by mixing oxidizing enzymes with corn pericarp components ferulic acid and coumaric acid were typically less preferred/more toxic to caterpillars such asHelicoverpa zea (Boddie) and sap beetles such asC. lugubris. Thus, enhanced browning of maize pericarp can promote resistance to insects and is at least partly influenced by the presence of oxidizing enzymes. This mechanism may also promote resistance to maize pathogens, including those that produce mycotoxins.