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Maize Ribosome-Inactivating Protein Inhibits Normal Development of Aspergillus nidulans and Aspergillus flavus

February 2001 , Volume 14 , Number  2
Pages  164 - 172

Kirsten Nielsen , 1 Gary A. Payne , 2 and Rebecca S. Boston 1

1Department of Botany, North Carolina State University, Box 7612, Raleigh 27695-7612, U.S.A.; 2Department of Plant Pathology, North Carolina State University, Box 7616, Raleigh 27695-7616; U.S.A.

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Accepted 18 October 2000.

The abundant maize kernel ribosome-inactivating protein 1 (RIP1) was tested for antifungal activity against Aspergillus nidulans and Aspergillus flavus. A microculture assay was developed to monitor fungal growth and development after treatment of conidia with RIP1 or control proteins. A striking decrease in hyphal proliferation was observed when conidia of A. nidulans, a genetically well-characterized nonpathogenic species, were treated with RIP1 protein. Treatment with a RIP1 mutant protein that lacked enzymatic ribosome-inactivating activity caused no observable effects. RIP1 treatment of conidia from the maize pathogen A. flavus resulted in increased hyphal branching. Examination of the branched hyphae after Congo red staining revealed only one growing hyphal tip per conidium. These results indicate that both fungi were affected by RIP1 treatment, but the lysis seen with treatment of A. nidulans was apparently avoided by A. flavus. A developmental time course revealed that both fungal species were affected by RIP1 at the postdivisional growth stage. The inhibitory activity of RIP1 against normal fungal growth is consistent with a biological function to protect the seed from fungal invasion.

Additional keywords: b-32, plant defense, seed protein, Zea mays L.

© 2001 The American Phytopathological Society