Ballhorn, Daniel J.; Heil, Martin; Schiwy, Susann; Jensen, Manfred:

Quantitative variability of direct chemical defense in primary and secondary leaves of lima bea

In: Journal of Chemical Ecology, Jg. 34 (2008) ; Nr. 10, S. 1298-1301
Zeitschriftenaufsatz / Fach: Biologie
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’ longlived
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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