Document: CAR-3-48-31

Anti-herbivore responses in the field: Interactions between wound- and UV-B induced defenses.

MAZZA, C.A.* ¹, C.L.BALLARÉ ¹, J.W.STRATMANN ², C.A.RYAN ² and J.ZAVALA ¹

University of Buenos Aires, Buenos Aires, Argentina. ¹
Washington State University, Pullman, WA , USA. ²

Abstract:
Exposure of plants to solar ultraviolet-B (UV-B) radiation frequently reduces insect herbivory in the field. This is in part a result of changes induced by solar UV-B affecting plant tissue quality. In particular, solar UV-B can induce the production of tougher leaves, with higher levels of phenolic compounds, which may deter leaf consumption by some insects. In addition, laboratory experiments have recently shown that high doses of UV-B can potentiate the accumulation of proteinase inhibitors (PI), which are defensive anti-herbivore proteins induced by wounding. The accumulation of PIs is mediated through the jasmonic acid (JA) signaling pathway, which is also thought to mediate some defense responses induced by UV-B. We have carried out field experiments in Buenos Aires with a tomato mutant that is deficient in JA production (def1), and two wild-type (WT) lines (cv. Castlemart and Platense). We investigated: (1) The roles played by the JA signaling pathway in anti-herbivory defenses under field conditions; and (2) The interaction between this signaling pathway and UV-B-induced responses. The damage inflicted by naturally-occurring populations of chewing insects was much higher in def1 than in the WT plants, confirming the important role of JA-induced defenses. As expected, PI levels were much lower in def1 than in the WT lines. Interestingly, however, exposure of def1 plants to solar UV-B resulted in a marked reduction in the severity of leaf herbivory. Solar UV-B increased the content of crude phenolics in all three genotypes. These results suggest that the increased production of at least some soluble phenolics triggered by solar UV-B does not depend on JA signaling, and this phenolic response might explain the increased resistance to herbivores displayed by def1 plants exposed to solar UV-B.

Keywords: plant-insect interaction, proteinase inhibitors, UVB

This abstract is being presented at: 10:30 AM in session:
Poster Session #14: UV-B.