Barley (Hordeum vulgare L.) that is infested with Fusarium head blight (FHB, `scab') is unsuitable for
malting and brewing because it may contain mycotoxins and has unacceptable malting quality. Fungal
proteinases are apparently often involved in plant-microbe interactions, where they degrade storage
proteins, but very little is known about the enzymes that the fungi produce in the infected grain. We have
shown previously that one plant pathogenic fungus, Fusarium culmorum, produced subtilisin- and trypsinlike
enzymes when grown in a cereal protein medium. To establish whether these proteinases were also
synthesized in FHB-infested barley in vivo, ®eld-grown barley was infested as the heads emerged. Extracts
were prepared from the grain as it developed and matured and their proteolytic activities were measured
with N-succinyl-Ala-Ala-Pro-Phe p-nitroanilide and N-benzoyl-Val-Gly-Arg p-nitroanilide. The heavily
infested barleys contained both subtilisin- and trypsin-like activities. These enzymes reacted with
antibodies prepared against each of the two F. culmorum proteinases, indicating that those produced in the
laboratory cultures and in the ®eld-infested barley were the same. The presence of these proteinases
correlated with the degradation of speci®c buffer-soluble proteins in the infested grains. These enzymes
readily hydrolyzed barley grain storage proteins (C- and D-hordeins) in vitro. The presence of these
Fusarium proteinases in the barley indicates that they probably play an important role in the infestation,
but exactly how and when they function is not clear.
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