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United States Department of Agriculture

Agricultural Research Service

Title: The influence of intact-plant and excised-leaf bioassay designs on volicitin- and jasmonic acid-induced sesquiterpene volatile release in zea mays

Authors
item SCHMELZ, ERIC
item Alborn, Hans - ENT. DEPT. UNIV FLA
item Tumlinson Iii, James

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 23, 2001
Publication Date: July 17, 2001
Citation: Schmelz, E.A., Alborn, H.T., Tumlinson Iii, J.H. 2001. The influence of intact-plant and excised-leaf bioassay designs on volicitin- and jasmonic acid-induced sesquiterpene volatile release in zea mays. Planta. 214:171-179.

Interpretive Summary: When corn plants are damaged by beet armyworm caterpillars feeding on the leaves they emit a blend of volatile chemicals, that attracts parasites and predators, natural enemies of the caterpillars. Plant volatile production is in response to insect derived factors, termed elicitors. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have discovered that excised plants release a greater amount elicitor induced volatiles than similarly treated intact plants. Excision also changes the blend of volatiles produced. This suggests that drought and other forms of stress may increase the plants ability to attract natural enemies of the herbivores. Also both intact and excised plant assays need to be considered as the plant responses are very different. These results suggest that it may be possible to investigate changes in excised plants that enable greater volatile production following insect attack. In collaboration with genetic engineering, increased volatile production would enable plants to defend themselves more effectively against insect pests.

Technical Abstract: Induced plant responses to insect attack include the release of volatile chemicals which are used as host location cues by the natural enemies of insect herbivores. Volicitin (N-(17-hydroxylinolenoyl)-L- glutamine), identified in beet armyworm (Spodoptera exigua) oral secretions, stimulates volatile production in corn seedlings and is hypothesized to trigger induced volatile production by modulating levels jasmonic acid (JA). We compare the sesquiterpene volatile production of damaged leaves treated with either aqueous buffer, volicitin, or JA. Treatments were performed at three different times (Evening, Midnight, or Morning) and volatiles were collected in the following photoperiod. Both JA and volicitin treatments stimulated the release of volatile sesquiterpenes, namely caryophyllene, bergamotene, and farnesene. In all cases, JA stimulated significant sesquiterpene production while volicitin induced production occurred only in the excised bioassays and the Midnight intact plants. On average, excised leaves produced a 2.5- to 8.0- fold greater volatile response than similarly treated intact plants. Excision also altered the ratio of induced sesquiterpene production by preferentially increasing farnesene production. Sesquiterpene production was highest in the Midnight excised plants and lowest in the Morning intact plants. On average, JA produced a sustained production of sesquiterpenes over time while the response following volicitin treatment was more transient. Quantitative differences between intact and excised plants leaves suggest that excised assay results should be cautiously

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