Substrate Utilization by Aspergillus flavus in Inoculated Whole Corn Kernels and Isolated Tissues

Abstract

Utilization of the major corn (Zea mays) reserve materials (free saccharides, starch, triglycerides, and zein) was monitored during infection of detached kernels by Aspergillus flavus (A. flavus) over a 12-day period. Inoculated whole kernels were compared to noninoculated kernels. Concentrations of sucrose and raffinose in inoculated seed decreased to nearly zero at 6 days, whereas concentrations of these saccharides in noninoculated seed dropped at a considerably slower rate, and significant levels remained at the end of the incubation period. Triglyceride concentrations remained unchanged in the noninoculated seed but dropped continuously after 2 days in the inoculated seed. Starch and zein concentrations did not change during the 12-day incubation period. Aflatoxin B1 was first detected after 2 days and increased to about 20 microg/g (20,000 ppb) after 12 days. Very low aflatoxin concentrations were detected in the noninoculated seed. Significant concentrations of erythritol, arabitol, and mannitol were produced during infection, with peak concentrations occurring at 8 days. Whole seed and germ tissue appeared to support good fungal growth and aflatoxin production, whereas ground tissues and endosperm did not. A. flavus preferentially utilized saccharides as initial carbon substrates followed by triglycerides. When invading nonwounded corn kernels, the fungus selectively targets the germ tissue where these materials are localized in the highest concentrations.

Aflatoxins, fumonisins, and trichothecenes: a convergence of knowledge

“…Keller et al (1994) followed colonization and aflatoxin production in maize kernel tissues with strains of A. flavus and A. parasiticus that accumulate the orange-colored, pathway metabolite norsolorinic (NOR), which accumulate due to a partial block in the aflatoxin biosynthetic pathway. During colonization, little degradation of starch and storage proteins occurs (Mellon et al, 2005). When inoculated to wounded kernels, the embryo was colonized by the fungus within 4 days, and nearly all the NOR and aflatoxin accumulated in the embryo tissues.…”

Genetic regulation of aflatoxin biosynthesis: From gene to genome

“…Not surprisingly, evidence has shown that Malonyl-CoA is needed for biosynthesis of AF (Dutton, 1988). In corn, A. flavus is preferentially associated with the germ region of infected kernels (Fennell et al, 1973;Lillehoj et al, 1974); this lipid rich germ tissue also appears more amenable to AF production than the whole kernel (Mellon et al, 2005).…”

Comparison of Volatiles Profile and Contents of Trichothecenes Group B, Ergosterol, and ATP of Bread Wheat, Durum Wheat, and Triticale Grain Naturally Contaminated by Mycobiota

“…This indicates the relationships between individual groups of compounds, i.e., volatiles, non-volatiles, fungal biomass indicators and mycotoxins, and shows volatile compounds to have an inhibitory effect on the growth of other microscopic fungi (Mellon et al, 2002, 2005). …”