Germination Induces Accumulation of Specific Proteins and Antifungal Activities in Corn Kernels

Abstract

This study examined protein induction and accumulation during imbibition and germination of corn kernels, as well as antifungal activities of extracts from germinating kernels against Aspergillus flavus and Fusarium moniliforme. Genotypes studied included GT-MAS:gk and Mp420, which are resistant to A. flavus infection and aflatoxin accumulation, and Pioneer 3154 and Deltapine G-4666, which are susceptible to A. flavus infection and aflatoxin accumulation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis resolved five protein bands that were present at higher concentrations in germinated kernels than in nongerminated kernels. Western blot analyses revealed that one of these proteins reacted with the 22-kDa zeamatin antiserum, and a zeamatin-like protein accumulated to a higher concentration in germinated kernels. Two protein bands from dry kernels that reacted with ribosome-inactivating protein (RIP) antiserum were identified as the 32-kDa proRIP-like form and an 18-kDa peptide of the two peptides that form active RIP. However, in germinated kernels, two protein bands that reacted with RIP antiserum were identified as two RIP-like peptides with a molecular mass of approximately 18 and 9 kDa. Purified RIP and zeamatin from corn inhibited growth of A. flavus. Bioassays of germinated kernel extracts from all four genotypes exhibited antifungal activity against A. flavus and F. moniliforme, with extracts from the susceptible genotypes showing greater inhibition zones. This study provides evidence of protein induction in corn kernels during imbibition or the early stages of germination, and the induced proteins may be related to our previous findings of germination-associated resistance in the corn kernel, especially in the susceptible kernels.

Detoxification of Corn Antimicrobial Compounds as the Basis for Isolating Fusarium verticillioides and Some Other Fusarium Species from Corn

“…In an effort to identify host resistance factors, various plant defense responses to F. verticillioides infection of germinating kernels have been studied (9,14,21). In addition to these protein-based defenses, maize begins to synthesize and store chemical defenses once germination is initiated.…”

Identifying Aflatoxin Resistance-related Proteins/Genes through Proteomics and RNAi Gene Silencing1

“…Using this assay, Brown et al (1993) demonstrated the existence of a subpericarp resistance in maize kernels and that the expression of this resistance requires a viable embryo, indicating that biochemical factors may play a major role in resistance. Guo et al (1997) found preimbibition significantly increased aflatoxin resistance of susceptible maize genotypes. Further investigation revealed that susceptible genotypes were able to induce the same antifungal proteins as resistant lines upon fungal infection, but at a slower pace or at lower levels compared to resistant maize lines .…”

Development of Maize Host Resistance to Aflatoxigenic Fungi

“…Examinations of kernel proteins of several genotypes revealed differences between genotypes resistant and susceptible to aflatoxin contamination [39]. Imbibed susceptible kernels, for example, showed decreased aflatoxin levels and contained germination-induced ribosome inactivating protein (RIP) and zeamatin [40]. Both zeamatin and RIP have been shown to inhibit A. flavus growth in vitro [40].…”

“…Imbibed susceptible kernels, for example, showed decreased aflatoxin levels and contained germination-induced ribosome inactivating protein (RIP) and zeamatin [40]. Both zeamatin and RIP have been shown to inhibit A. flavus growth in vitro [40]. In another study, two kernel proteins were identified from a resistant corn inbred (Tex6) which may contribute to resistance to aflatoxin contamination [41].…”