cotine, increases after herbivore
attack in the native, post-fire annual, Nicotiana attenuata,
and is internally activated by the wound-hormone, jasmonic
acid. The roots of plants were treated with the methyl ester
of this hormone (methyl jasmonate; 500g suspended in 10 ml
water, while control members of the pair were treated with 10
ml water) to elicit a response in one member of each of 745
matched pairs of plants growing in native populations in
southwestern Utah (USA) with different probabilities of
attack from herbivores (primarily rabbits and the larvae of
the tobacco specialist, Manduca sexta).The lifetime
production of viable seed was measured from all plants to
determine the fitness consequences of jasmonate induction.
The results strongly support the cost-benefit model for
inducible defenses. Jasmonate treatment significantly
increased nicotine concentrations in the leaves of treated
plants 22-54% above those of their control,
water-treated counterparts. In populations where plants were
being heavily attacked (populations IIA, B), nicotine
concentrations of leaves from control plants were comparable
to those of unattacked jasmonate-induced plants from the
other populations, but the effect of jasmonate treatment was
retained; clearly, the jasmonate treatment had not saturated
the plants' nicotine response. How do these changes
affect plant fitness as estimated by their lifetime viable
seed production? The answer depends critically on the
plant's environment, particularly, the likelihood of
herbivore attack.
For plants in environments with high herbivory (the
2-year-old burns, populations IIA, B), the benefit of
jasmonate-treatments could be readily seen. For example, in
population IIA, 10 days after the treatment, 33% of the
control plants had lost more than 40% of their leaf area to
herbivores,
'"/>Contact: Ian T. Baldwin
Baldwin@ice.mpg.de
49-3641-6436-59
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