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

Different Aspergillus species (flavus, parasiticus, and nidulans), whi ch produce different intermediates and end products of the aflatoxin p athway (norsolorinic acid, NOR; sterigmatocystin, ST; and aflatoxin, A F), are useful in studying the maize-Aspergillus-mycotoxin interaction . Aspergillus AF mutants, which produce NOR (a visible orange intermed iate of both ST and AF), were used to visualize mycotoxin deposition i n host and fungal tissues. NOR was seen in specific maize kernel tissu es (embryo and aleurone) and specific fungal tissues (substrate myceli um but not sporulating mycelium) within 24 h after inoculation of kern els or growth media. ST and AF were found in the same maize tissues on ly after organic extracts of these tissues were quantitated by time-co nsuming chromatography methodologies. Mycotoxin production and fungal ingress by all three Aspergillus spp. were subject to regulation by th e developmental stage of the maize kernel: both fungal colonization an d NOR deposition shifted from embryonic to endosperm tissues in germin ating maize kernels. The appearance of NOR flagged the progress of fun gal invasion through kernel tissues. We suggest that NOR mutants may b e useful tools to identify likely infection sites in maize kernels and that the genetically characterized A. nidulans may be useful in helpi ng identify global regulatory mechanisms in the maize-Aspergillus-myco toxin interaction.