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Abstract:
Plants of the Brassicaceae are defended from feeding by generalist insects by constitutively-expressed and
herbivory-induced glucosinolates (GS). We induced
Arabidopsis plants 1, 16 and 24 h prior to allowing neonate
larvae of the generalist Helicoverpa armigera to feed on
whole plants for 72 h. These plants were subsequently retested
with another group of neonates for a further 72 h. We used
wild-type A. thaliana Col-0, and mutant lines lacking indolic
GS, aliphatic GS or all GS.We hypothesized that larvaewould
not grow well on defended plants (WT) compared to those
lacking GS, and would not grow well if plants had been
primed or fed on for longer, due to the expected induced
GS. There was survivorship on all lines suggesting
H. armigera is a suitable generalist for these experiments.
Larvae performed less well on wild-type and no indolic lines
than on no aliphatic and no GS lines. Larvae distributed feeding
damage extensively in all lines, more so on wild type and
no-indolic lines. Contrary to expectations, larvae grew better
on plants that had been induced for 1 to 16 h than on uninduced
plants suggesting they moved to and selected less
toxic plant parts within a heterogeneously defended plant.
Performance declined on all lines if plants had been induced
for 24 h, or had been fed upon for a further 72 h. However,
contrary to expectation, individual and total GS did not increase
after these two treatments. This suggests that
Arabidopsis plants induce additional (not GS) defenses after longer induction periods.
