Nicotiana attenuata synthesizes the toxic alkaloid, nicotine, in its roots and dramatically increases its rate of nicotine synthesis after leaf wounding and herbivory, which, in turn, results in a systemic increase in nicotine concentrations in both vegetative and reproductive tissues. In laboratory feeding trials, induced levels of nicotine protect plants against nicotine-tolerant herbivores, but these herbivores may suffer lower rates of parasitisms when feeding on plants with high nicotine concentrations, indicating that this induced defense may have both ecological benefits and costs. Moreover, 6% of an N. attenuata plant's total nitrogen content is in this toxin alone in an induced plant, and this nitrogen is not available for other activities such as seed production, suggesting that inducing nicotine production may incur large resource-based costs. Hence, it is reasonable to suppose that the fitness consequences of producing this toxin will vary greatly depending on the plant's habitat.

The discovery of the endogenous wound signals which plants use to activate induced responses, have provided researchers with valuable tools to activate defenses independently of herbivore attack in plants growing in their native habitats. Jasmonic acid, a ubiquitous wound-hormone known to increase the synthesis of diverse defense-related metabolites, is strongly implicated as a long-distance endogenous wound-signal activating nicotine synthesis in the roots after leaf wounding and it is reasonable to propose that the treatments of roots with jasmonate will stimulate responses comparable to those elicited by leaf wounding.

N. attenuata has life history characteristics that make it particularly useful for a test of the cost-benefit model for induced defenses. It is an ephemeral member of the annual community in bu
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Contact: Ian T. Baldwin
Baldwin@ice.mpg.de
49-3641-6436-59
Max-Planck-Gesellschaft
9-Jul-1998


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