ARS | Publication request: Physical characteristics of Medicago truncatula calcium oxalate crystals determine their effectiveness in insect defense

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: June 1, 2009
Publication Date: July 1, 2009
Citation: Korth, K.L., Park, S., Nakata, P.A., Nagarajan, R., McGehee, Jr., R.E. 2009. Physical characteristics of Medicago truncatula calciumoxalate crystals determine their effectiveness in insect defense [abstract]. Model Legume Congress, July 12-16, 2009, Pacific Grove, California. p: 133.

Technical Abstract: Plant structural traits 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. have previously been shown to be effective deterrents of lepidopteran insect feeding. They are also inhibitors of conversion of plant material into insect body mass during or after consumption. Growth of Spodoptera exigua Hubner, beet armyworm, larvae was correspondingly greater on calcium oxalate defective (cod) mutants of M. truncatula with lower levels of crystal accumulation. Insects feeding on M. truncatula leaves with calcium oxalate crystals experience greater negative effects on insect growth and mandible wear than those feeding on artificial diet amended with smaller amorphous crystals from commercial preparations. Commercial calcium oxalate can be added to insect artificial diet at levels up to 7.5-fold higher than levels found in wildtype M. truncatula leaves with minimal effect on insect growth or lepidopteran mandibles. The data suggest that negative impacts of calcium oxalate in the diet of 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 physical effects that M. truncatula-derived crystals have on insect mandibles, no damage was detected in insect peritrophic gut membranes due to consumption of these crystals. Taken together, the data indicate that the size and shape of prismatic M. truncatula oxalate crystals are important factors in determining effects on insect growth. If manipulation of calcium oxalate is to be used in developing improved insect resistance in plants, then controlling not only the overall amount, but also the size and shape of crystals, could be valuable traits in selecting desirable plant lines.