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Neutron tomography was studied as a technique for non-destructively analyzing the internal structure of dried corn kernels. The study had two goals: first, to determine if the analysis could identify well-known anatomical features of the kernels; and second, to determine if it could distinguish between different types and treatments of kernels. Specifically, kernels which were infected vs. uninfected with the aflatoxin-producing fungus Aspergillus flavus were analyzed. Two different varieties of corn were used: VA35 (susceptible to A. flavus infection) and GT-MAS:gk (resistant). It was found that many anatomical features of the kernels could be identified using neutron tomography, including the scutellum, endosperm, aleurone, pericarp, pedicel, coleorhizae, radical, plumule, and coleoptile. Furthermore, differences were detected between susceptible kernels that had been inoculated and those that had not. Infected kernels were found to have lower neutron attenuation in the scutellum and embryo regions, possibly caused by lower hydrogen concentrations due to fungal degradation. No systematic structural differences were detected between resistant inoculated and resistant uninoculated kernels, as expected. This study indicated that neutron tomography could be a useful technique for the structural analysis of corn, and possibly other grains or small biological objects.

The activity of kievitone hydratase (KHase)—the enzyme catalysing detoxification of the phytoalexin, kievitone, to kievitone hydrate (KH)—in extracts of Fusarium solani f. sp. phaseoli -infected hypocotyls of Phaseolus vulgaris increased for several days and reached a peak at 5 days after inoculation. Several variants of the virulent isolate of F. solani f. sp. phaseoli were obtained, either following exposure of the fungus to the mutagenic chemical, N-methyl-N′-nitro-N-nitrosoguanidine, or by making transfers from naturally occurring sectors in agar cultures. These variants were monitored for pathogenicity to bean, sensitivity to kievitone and ability to cause clearing of an opaque, kievitone-amended, modified Fries agar—an assay which indicated KHase activity. All variants with reduced KHase activity were more sensitive to kievitone and were less pathogenic to bean than the virulent strain from which they were derived. No virulent isolate that lacked KHase was found. The presence of KHase in Fusarium -infected bean tissues soon after inoculation, and for several days thereafter, as well as the association between lowered KHase activity and reduced virulence, suggest that this enzyme plays a role in the development of the fungus in its host's tissues. Furthermore, these results are consistent with detoxification of the isoflavonoid, kievitone, by F. solani f. sp. phaseoli being important to the pathogenic behavior of this fungus.

Kievitone hydratase (KHase), an enzyme which catalyses detoxification, of the phytoalexin kievitone, was isolated from cell-free culture filtrates of Fusarium solani f. sp. phaseoli. Partial purification was achieved by anion exchange chromatography, gel filtration and gradient Polyacrylamide disc gel electrophoresis. Gel filtration and electrophoresis gave molecular weight estimates of 173 000 and 102 000, respectively. Based on the results of isoelectric focusing and affinity chromatography, KHase is an acidic (pI= 5·1±0·6) glycoprotein. Most enzymic activity was retained after exposure of KHase to sodium periodate oxidation for 24 h. Further characterization revealed that the enzyme had a temperature optimum of 55°C, but denatured rapidly at or above 70°C. The pH optimum was 5·5 at 27°C with an apparent Km of 1·75×10−6 M under these conditions. Preliminary findings indicated that KHase occurred in Fusarium-infected bean tissues.