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Changes in
the glucosinolate-myrosinase defense system in Brassica juncea cotyledons during
seedling development.
J Chem Ecol. 2002 Feb;28(2):243-56.
Wallace SK, Eigenbrode SD.
Department of Plant, Soil, and Entomological Sciences, University of Idaho,
Moscow 83844-2339, USA.
Optimal defense theory (ODT) predicts that plant defenses will be allocated to
plant organs and tissues in proportion to their relative fitness values and
susceptibilities to attack. This study was designed to test ODT predictions on
the myrosinase-glucosinolate defense system in Brassica juncea by examining the
relationships between the fitness value of B. juncea cotyledons and the levels
and effectiveness of cotyledon defenses. Specifically, we estimated fitness
value of cotyledons during plant development by measuring plant growth and seed
production after cotyledon damage or removal at successive seedling ages.
Cotyledon removal within five days of emergence had a significant impact on
growth and seed production, but cotyledon removal at later stages did not.
Consistent with ODT, glucosinolate and myrosinase levels in cotyledons also
declined with seedling age, as did relative defenses against a generalist
herbivore, Spodoptera eridania, as estimated by bioassay. Declines in
glucosinolates were as predicted by a passive, allometric dilution model based
on cotyledon expansion. Declines in myrosinase activity were significantly more
gradual than predicted by allometric dilution, suggesting active retention of
myrosinase activity as young cotyledons expand.
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