For most plants, growth under elevated CO2 results in increased biomass since photosynthesis rates are increased; however, this increase is accompanied by a decrease in leaf percent nitrogen and an increase in C:N ratio. Therefore, in the future, plants may have less nitrogen available for important internal processes. Many studies have demonstrated that constitutive levels of carbon-based defenses, including phenolics, increase when plants are grown under the elevated CO2 levels Earth will have later this century. However, almost nothing is known about the inducibility of plant chemical defenses under elevated CO2. In this study, the response of both constitutive and inducible defenses to elevated carbon dioxide levels will be examined in tomato. Tomato contains carbon-based phenolics, several alkaloids (e.g. tomatine and solanine, which contain a moderate amount of nitrogen), and protease inhibitors, which contain high amounts of nitrogen. The following hypotheses will be specifically examined: 1.Constitutive levels of phenolics will increase in the tomato plants grown at elevated CO2 levels, but constitutive levels of alkaloids and protease inhibitors will remain the same or decrease. 2.Inducibility of phenolics, alkaloids and protease inhibitors will decrease when tomato plants are grown at elevated CO2. 3.Inducibility of compounds containing the most nitrogen (protease inhibitors) will decrease most while inducibility of phenolics will decrease least. The decrease in inducibility of alkaloids will be at a level between that of protease inhibitors and phenolics since alkaloids contain some nitrogen. 4.Plants whose leaves have the highest nitrogen concentrations will have the smallest decrease in inducibility of all three compounds, and this relationship will be stronger in plants grown at elevated CO2 levels than in those grown at ambient CO2 levels.