9505950 Baldwin Many native plants increase the concentration of toxic metabolites in their tissues when they are attacked by herbivores. While understanding of the mechanisms responsible for these responses has advanced rapidly, understanding of their significance remains limited. Do these wound-induced responses function as defenses, making plants more resistant to further attack? If these responses protect plants, why are the defenses inducibly deployed? Two classes of theories have been proposed to explain inducibility: 1) theories which assume that the inducible trait is a cost-savings measure which reduces the resource cost of defense by allowing plants to time the allocation of resources to defense with the need for defense, and 2) theories which do not make this assumption. This research examines these questions by testing both the benefits and the costs of an induced alkaloidal defense to plant fitness in the field by using 1) a recently identified damage signal which activates the induced defense, and 2) an inhibitor of enzymes responsible for producing the damage signal, which will allow suppression of the induced defense in attacked plants. The results of this work will be important for the development of sustainable agricultural practices by developing approaches to pest resistance that move away from the exogenous addition of pesticides. Transgenic technology has greatly facilitated the ability to move potent resistance traits among different species and controlling the expression of these traits in crop plants. Understanding the costs and benefits of different types of expression is essential if these new traits are to be sustainable in agriculture.
