Submitted to: Journal of Cereal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/21/2003
Publication Date: 8/21/2003
Citation: PEKKARINEN, A.I., KLEEMOLA, T., LAITILA, A., HAIKARA, A., JONES, B.L. FUSARIUM SPECIES SYNTHESIZE ALKALINE PROTEINASES IN INFESTED BARLEY. JOURNAL OF CEREAL SCIENCE. 2003. v. 37. p. 349-356. Interpretive Summary: In recent years the fungus Fusarium has caused a lot of damage to barley crops in the Upper Midwest. Fusarium-infested barley is unsuitable for malting and brewing because it contains toxins and has poor malting quality. One aspect of malting quality that is destroyed is the ability of the germinating barley to dissolve correct amounts of protein. Infested barleys produce too much soluble protein during malting and we wanted to ascertain whether this also occurred in field-grown grain. Field-grown grain was infected with Fusarium spores and samples of the maturing grain were collected and tested to see whether two Fusarium proteinase enzymes, which we had previously discovered, were present and active. The heavily infested barleys contained two Fusarium enzymes and antibody studies showed they were the same as the ones we had studied earlier in the laboratory. The enzymes apparently destroyed specific buffer-soluble proteins in the growing grains and, when purified, degraded the major barley storage proteins in laboratory experiments. These findings indicate that these enzymes play an important role when Fusarium invades barley plants, but their exact function is still not known. The import of this study is that it shows plant breeders and other researchers that they may be able to protect barley plants from Fusarium attack by destroying its ability to degrade their proteins. It also shows that they can most readily do this by destroying the abilities of these two specific Fusarium enzymes to function inside the grain.
Technical Abstract: 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 involved in plant-microbe interactions, because they degrade the storage proteins. We have shown previously that one plant pathogenic fungus, Fusarium culmorum, produced subtilisin- and trypsin-like enzymes when grown in a cereal protein medium. To establish whether these proteinases were also synthesized in FHB-infested barley in vivo, field-grown barley was infested as the kernels emerged. Grain extracts were prepared 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 field-infested barley were the same. The presence of these proteinases correlated with the degradation of specific 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 they function is not clear.