Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2008
Publication Date: 2/26/2008
Citation: Sobolev, V.S. 2008. Localized Production of Phytoalexins by Peanut (Arachis hypogaea) Kernels in Response to Fungal Invasion. Journal of Agricultural and Food Chemistry. 56(6):1949-1954. Interpretive Summary: Peanut is capable of naturally resisting infection by pathogens, including fungi that can produce carcinogenic afalatoxins. In response to fungal infection peanuts produce several, so called phytoalexins, defensive compounds that protect peanuts from pathogens. One of the major peanut phytoalexins, resveratrol, is known to exert manifold biological effects that are not limited to the host plant, but found to be beneficial also to human health. However, the mechanism and dynamics of peanut resistance to external invasion has not been explored. Our previous research demonstrated that diverse peanut genotypes grown in the field side-by-side exhibited different responses to fungal attack producing significantly different amounts of phytoalexins. The objective of this research was to study the phytoalexin production by wounded kernels of a single peanut cultivar (Georgia Green) in response to infection by different fungal strains. The dynamics of phytoalexin production was studied by dissecting kernel layersat different depths starting from the infected area down to healthier tissues. Six peanut phytoalexins were detected in the kernel slices and quantitated. The composition of phytoalexins varied significantly as layer depth increased. After 24 h of incubation with the fungus, tissues remote from the infected area produced almost exclusively trans-resveratrol, while closer to the infected area tissues synthesized at least six phytoalexins. This fact suggests that resveratrol is the starting building block for the synthesis of related phytoalexins. There was no relationship between phytoalexin production and toxin-producing ability of fungal strains that elicited their production.
Technical Abstract: Peanuts respond to fungal infection by synthesizing phytoalexins, most of which are antibiotic stilbenes. The mechanism and dynamics of phytoalexin formation in the peanut has not been studied. One of the most popular peanut cultivars in the southeastern U.S., Georgia Green, was investigated for its ability to produce phytoalexins in response to infection by soil fungal strains. The experimental design allowed for study of phytoalexin production in peanut kernels layer-by-layer. The layers were dissected from different depths of the kernel starting from the infected area down to healthier tissues. Six peanut phytoalexins, trans-resveratrol, trans-arachidin-1, trans-arachidin-2, trans-arachidin-3, trans-3-isopentadienyl-4,3',5'-trihydroxystilbene, and SB-1 were detected in the kernel slices and quantitated. All of the fungal strains triggered phytoalexin production; however, the composition of phytoalexins varied significantly by layer. After incubation for 24 h tissues remote from the infected area produced almost exclusively trans-resveratrol, while closer to the infected area tissues synthesized all six phytoalexins. In all the experiments, after 48 h of fungal growth deeper layers produced all tested phytoalexins. There was a significant difference in phytoalexin production elicited by some fungal isolates. No association was observed between phytoalexin production and toxigenic potential of fungal strains that elicited the production in mature peanut kernels.