ARS | Publication request: Structural and chemical insect defenses in calcium oxalate defective mutants of Medicago truncatula

Submitted to: Plant Molecular Biology International Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: October 1, 2009
Publication Date: October 1, 2009
Citation: Korth, K., Park, S., Nakata, P.A., Nagarajan, R., McGehee, R. 2009. Structural and chemical insect defenses in calcium oxalate defective mutants of Medicago truncatula [abstract]. Proceedings, 9th Congress International Society for Plant Molecular Biology. October 25-30, 2009, St. Louis, Missouri. p. 187.

Technical Abstract: Plant structures can act as defense against herbivorous insects, causing them to avoid feeding on a given plant or tissue. Mineral crystals of calcium oxalate in leaves of Medicago truncatula Gaertn. are effective deterrents of lepidopteran feeding, and they inhibit conversion of leaves into insect body mass after consumption. Growth of Spodoptera exigua Hubner, beet armyworm, larvae is greater on calcium oxalate defective (cod) mutants of M. truncatula with decreased crystal accumulation. Insects feeding on M. truncatula with calcium oxalate crystals experience negative effects on growth and mandible wear compared to those feeding on artificial diet amended with smaller crystals. Commercial calcium oxalate can be added to an artificial diet at 7.5-fold higher concentrations than found in wildtype M. truncatula leaves with minimal effect on insect growth or mandibles. The data suggest that negative impacts of calcium oxalate on larvae are due to physical factors, and not toxicity of the compound, as high levels of the commercial crystals are readily tolerated. In contrast to the dramatic effects that M. truncatula-derived crystals have on insect mandibles, no damage was detected in insect gut membranes due to consumption of crystals. The size and shape of M. truncatula oxalate crystals therefore appear to be the critical factors governing the negative effects on insect growth. If manipulation of calcium oxalate is to be used in developing improved insect resistance in plants, then the selection of traits that determine not only the amount, but also size and shape of crystals, would be of value in the selection of plant lines.