A VISUAL-PATTERN OF MYCOTOXIN PRODUCTION IN MAIZE KERNELS BY ASPERGILLUS SPP

Different Aspergillus species (flavus, parasiticus, and nidulans), which produce different intermediates and end products of the aflatoxin pathway (norsolorinic acid, NOR; sterigmatocystin, ST; and aflatoxin, AF), are useful in studying the maize-Aspergillus-mycotoxin interaction. Aspergillus AF mutants, which produce NOR (a visible orange intermediate of both ST and AF), were used to visualize mycotoxin deposition in host and fungal tissues. NOR was seen in specific maize kernel tissues (embryo and aleurone) and specific fungal tissues (substrate mycelium but not sporulating mycelium) within 24 h after inoculation of kernels or growth media. ST and AF were found in the same maize tissues only after organic extracts of these tissues were quantitated by time-consuming chromatography methodologies. Mycotoxin production and fungal ingress by all three Aspergillus spp. were subject to regulation by the developmental stage of the maize kernel: both fungal colonization and NOR deposition shifted from embryonic to endosperm tissues in germinating maize kernels. The appearance of NOR flagged the progress of fungal invasion through kernel tissues. We suggest that NOR mutants may be useful tools to identify likely infection sites in maize kernels and that the genetically characterized A. nidulans may be useful in helping identify global regulatory mechanisms in the maize-Aspergillus-mycotoxin interaction.