Abstract
BackgroundBecause of the increasingly concern of consumers and public policy about problems for environment and for public health due to chemical pesticides, the search for molecules more safe is currently of great importance. Particularly, plants are able to fight the pathogens as insects, bacteria or fungi; so that plants could represent a valuable source of new molecules.ResultsIt was observed that Medicago truncatula seed flour displayed a strong toxic activity towards the adults of the rice weevil Sitophilus oryzae (Coleoptera), a major pest of stored cereals. The molecule responsible for toxicity was purified, by solvent extraction and HPLC, and identified as a saponin, namely 3-GlcA-28-AraRhaxyl-medicagenate. Saponins are detergents, and the CMC of this molecule was found to be 0.65 mg per mL. Neither the worm Caenorhabditis elegans nor the bacteria E. coli were found to be sensitive to this saponin, but growth of the yeast Saccharomyces cerevisiae was inhibited at concentrations higher than 100 μg per mL. The purified molecule is toxic for the adults of the rice weevils at concentrations down to 100 μg per g of food, but this does not apply to the others insects tested, including the coleopteran Tribolium castaneum and the Sf9 insect cultured cells.ConclusionsThis specificity for the weevil led us to investigate this saponin potential for pest control and to propose the hypothesis that this saponin has a specific mode of action, rather than acting via its non-specific detergent properties.
Highlights
Because of the increasingly concern of consumers and public policy about problems for environment and for public health due to chemical pesticides, the search for molecules more safe is currently of great importance
One of the most promising sources of such compounds is probably plants, which have developed many ways to fight against insects, as well as against fungal and bacterial attacks, and one of these is the use of insecticidal molecules
By purification of the entomotoxic compound, we found that M. truncatula seeds are mainly protected against weevil attack by a specific saponin, rather than by the Pea Albumin 1 subunit b (PA1b) peptide, but this toxic effect is currently restricted to the rice weevil among insects
Summary
Because of the increasingly concern of consumers and public policy about problems for environment and for public health due to chemical pesticides, the search for molecules more safe is currently of great importance. Insecticides in particular, are increasingly used around the world but are increasingly stigmatized because of their persistence and their toxicity to non-target organisms (impacting amphibians, aquatic wildlife, beneficial insects, such as bees and ladybirds, and even causing mortality among farmers, in developing countries [1,2,3]). Chemical treatments used to protect stored products are the source of the majority of chemical residues in cereals, subsequently found in processed products. High doses of these residues can be dangerous for consumers. One of the most promising sources of such compounds is probably plants, which have developed many ways to fight against insects, as well as against fungal and bacterial attacks, and one of these is the use of insecticidal molecules
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