Quantitative Variability of Direct Chemical Defense in Primary and Secondary Leaves of Lima Bean (<Emphasis Type="Italic">Phaseolus lunatus</Emphasis>) and Consequences for a Natural Herbivore |
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Authors: | Daniel J Ballhorn Susann Schiwy Manfred Jensen Martin Heil |
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Affiliation: | 1.Department of Botany/Plant Ecology,University of Duisburg-Essen,Essen,Germany;2.Departamento de Ingeniería Genética,CINVESTAV-Irapuato,Irapuato,Mexico |
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Abstract: | Ontogenetic variability in chemical plant defenses against herbivores is a common phenomenon, but the effects of this variability
on herbivore–plant interactions are little understood. In a previous study on lima bean (Phaseolus lunatus), we found a trade-off between cyanogenesis, a direct defense, and the release of herbivore-induced volatile organic compounds
(VOCs; mainly functioning as an indirect defense). Moreover, the expression of these two defenses could change during plant
ontogeny. The present study aimed at elucidating whether such ontogenetic changes in plant defense can affect herbivore–plant
interactions. We quantified feeding rates of a natural insect herbivore, the Mexican bean beetle (Epilachna varivestis), on primary and secondary leaves of individual lima bean plants. These insects strongly preferred low cyanogenic primary
leaves over high cyanogenic secondary leaves. Although weakly defended by cyanogenesis, lima beans’ primary leaves showed
protein concentrations and photosynthetic activities that did not differ significantly from secondary leaves at the time of
analysis. Based on our findings, we suggest that lima beans’ long-lived primary leaves function as efficient source organs,
even beyond the stage of seedlings. This hypothesis may explain why primary leaves express a strong indirect defense by the
release of herbivore induced VOCs. |
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Keywords: | Cyanogenesis Indirect defense VOCs Epilachna varivestis Feeding trial Trade-off Multiple defense syndromes |
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