|Tumlinson iii, James|
Submitted to: Plant Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/2/2003
Publication Date: 9/20/2003
Citation: Schmelz, E.A., Alborn, H.T., Tumlinson III, J.H. 2003. Nitrogen deficiency increases volicitin-induced volatile emission, Jasmonic Acid accumulation, and sensitivity in maize. Plant Physiology. 133:295-306. Interpretive Summary: Corn plants emit a blend of volatile chemicals shortly after attack by caterpillars and volatiles serve as attractants for predators and parasitoids, the natural enemies of caterpillars. Volatile emission is triggered by a chemical elicitors present in the caterpillar oral secretions; however, the activity of single purified elicitors can be highly variable between plants. It was hypothesized that this variation in volatile emission could be used to better understand important regulators of the process. Scientists at the Center for Medical, Agricultural and Veterinary Entomology in Gainesville, FL, have discovered that plant nitrogen levels greatly influence the activity of insect-derived elicitors. As nitrogen levels increase elicitor stimulated volatile emission decreases. Plants grown under low nitrogen exhibited increased sensitivity and expression of hormone levels that regulate volatile emission in response to elicitors. These results emphasize the importance of two interacting plant hormones that together regulate volatile emission and suggest the requirement of multiple elicitors. An understanding of the interaction of insect-elicitors and plant hormones that regulate volatile emission is critical in the development of plants with improved self-defense mechanisms that enable natural enemies to attack pests.
Technical Abstract: Caterpillar-induced plant volatile emission and the subsequent attraction of natural enemies is facilitated by fatty acid-amino acid conjugate (FAC) elicitors, such as volicitin (N-(17-hydroxylinolenoyl)-L-glutamine), present in herbivore oral secretions. Multiple lines of evidence suggest that both jasmonic acid (JA) and ethylene (E) mediate the magnitude of this variable response; however, the role of E is poorly understood. We examine the interaction of the volicitin, JA, E and volatile emission by regulating nitrogen availability, in the form of nitrate (N), and thus E sensitivity (He et al., 1992). In corn (Zea mays) seedlings, volicitin-induced maximal sesquiterpene volatile emission in N deficient plants while this response declined with increased N availability. Compared to Low N (0.2 mM), Medium N plants (2.0 mM) demonstrated a greater reduction in volicitin-induced volatiles than JA-induced volatiles, suggesting differences in elicitor-induced JA levels. Low N plants confirmed this altered induction of JA with greater sustained increases in wound and volicitin-induced JA levels compared to Medium N plants. Low and Medium N plants also differed greatly in ethylene sensitivity. In Low N plants, E synergized volicitin-induced volatile emission 4- to 12-fold with significant interactions first detected at 10 nL/L E. In Medium N plants interactions between volicitin and E were greatly reduced. E and the inhibitor 1-methylcyclopropene (1-MCP) increased and decreased voliticin-induced volatile emission, respectively; however, E did not increase nor did 1-MCP decrease JA levels. N availability influences plant perception and response to insect-derived elicitors through both altered JA kinetics and E sensitivity; however, we find no evidence of E promoting elicitor-induced JA levels.