Autotoxicity and chemical defense: nicotine accumulation and carbon gain in solanaceous plants

We quantified the accumulation of and tolerance to exogenously-fed nicotine by monitoring photosynthetic capacity and growth in two nicotine producing species of Solanaceous plants (Nicotiana sylvestris andN. glauca) as well as two Solanaceous species (Datura stramonium andLycopersicon esculentum) that do not produce nicotine to examine the relationship between tolerence and the ability to produce nicotine in defensive quantities. SinceN. sylvestris uses nicotine as an inducible defense, we examined whether nicotine tolerance is induced by damage to examine further the relationship between nicotine tolerence and synthesis. All species were grown in a 1 mM nicotine-containing hydroponic solution. Reductions in the photosynthetic capacity of nicotine-fed plants were found in all species tested. Nicotine-producing species showed no greater tolerance as measured by photosynthetic capacity than the two non-producing species. Leaf damage marginally increased the tolerence ofN. sylvestris to exogeneouslyfed nicotine suggesting that photosynthetic tolerance is coordinated with nicotine production in this nicotine-producing species.N. glauca plants regained photosynthetic capacity after their accumulated nicotine was demethylated to form nornicotine. Leaf nicotine pools in the other three species did not decrease, suggesting that for these species alkaloid metabolism does not play a major role in tolerance. Tolerance, as measured by biomass gained, was higher in the two non-producing species than in the nicotine-producing species suggesting that nicotine may also be functioning as a growth regulator. These results do not support the hypothesis that tolerance is as important as biosynthetic ability in determining which species accumulate defensively significant quantities of nicotine.