The distribution and abundance of nicotine in the tobacco, Nicotiana sylvestris: Optimal defense theory and correlations between nicotine, mass, and fitness

The positive correlation between leaf value and the within plant distribution of secondary metabolites is consistent with Optimal Defense (OD) theory predictions, but has not been examined experimentally. A substantial amount is known regarding the mechanism underlying the wound-induced whole plant (WP) nicotine response of tobacco (Nicotiana sylvestris Spegazzini and Comes (Solanaceae)). Jasmonic acid (JA) functions as an important component of the signal transduction pathway effecting wound-induced increases in nicotine production, a defense response to herbivore attack in N. sylvestris. We examine the relationships among leaf wounding, endogenous leaf JA pools, and whole plant (WP) nicotine accumulation over a range of wounding intensities and spatial distributions to explore Optimal Defense (OD) theory predictions for this induced defense. We find statistically significant, positive relationships among the number of leaf punctures, endogenous leaf JA, and WP nicotine accumulation, demonstrating that JA is an integral part of this wound response. Because the quantity of JA in a wounded leaf 90 minutes after wounding is a reliable indicator of the WP nicotine response to wounding, this trait provides insight into how plants integrate information about environmental insults and tailor their defense responses. Given our mechanistic understanding of this system, and evidence that nicotine induction exacts a fitness level cost, we used N. sylvestris to test the OD prediction that chemical defenses are allocated to tissues based upon tissue value. We correlated the effect of leaf removal on seed production with damage-induced leaf nicotine accumulation for plants over three developmental stages. We find that ontogenetic changes in leaf value and WP nicotine inducibility determine how a plant distributes its' defenses. Plants utilize systemic nicotine inductions at the rosette stage, switch to targeting of nicotine to the new and Y leaves at the elongation stage, and tend to defend the reproductive structures, but not the leaves at the flowering stage. Regardless of the mechanism behind the generation of relative leaf value and within plant nicotine distribution, throughout ontogeny plants defend their tissues in accordance with OD theory.