Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 6, 1998
Publication Date: N/A
Interpretive Summary: Cotton plants can be contaminated by a fungus that causes the cotton seed oil and cotton seed meal to be toxic. There are compounds called peptides that can kill fungi, and we plan to change the cotton plants so they will make these peptides. Cotton plants also make compounds called proteases that degrade peptides and cause them not to kill fungi. We have looked at the effect of these proteases from different parts of the cotton plant, on an antifungal peptide called cecropin, obtained from a moth. When cecropin was mixed with the cut outer layer of the cotton boll, the peptide was not degraded. However, when either the cotton boll outer layer or the seed was ground, the peptide was degraded. The fluid obtained from the cotton leaves also degraded the peptide. The cut sample of the cotton boll outer layer is actually closer to what is found in nature where cotton bolls are attacked by boll weevils causing small holes in the boll. Therefore, scientists should benefit from this research by knowing that cotton plants that are made to produce cecropin in the outer layer of the cotton boll can kill a fungal infection before it is degraded. If the antifungal peptide must be placed in the leaves or if they want to be sure the peptide won't degrade, then modifications to the peptide that will prevent the degradation will be needed.
Technical Abstract: We have examined the enzymatic degradation of the antimicrobial peptide, cecropin A, by proteases derived from the cotton boll pericarp, seed, or leaf. Different boll ages were used to ascertain when the production of protease occurred. Cecropin A was incubated with the tissue types for several time periods and the amount of cecropin remaining was determined by reversed-phase HPLC. It was found that cecropin was not significantly degraded by small circles cut from the pericarp, but the ground pericarp did cause partial degradation. The ground seed showed a large dependence on boll age for cecropin degradation with little degradation with 20-day- old bolls and complete degradation with 35-day-old bolls. The interstitial fluid extracted from cotton leaf was also shown to degrade cecropin A after 30 minutes of incubation. These data showed that genetically expressed cecropin A may deter microbial contamination and aflatoxin production in pericarp of the cotton bolls.