ALKALOIDAL RESPONSES TO DAMAGE IN NICOTIANA NATIVE TO NORTH-AMERICA

We performed field tests of alkaloid induction in Nicotiana attenuata plants growing in southwestern Utah with mimicry of the two major types of damage inflicted by invertebrate and vertebrate herbivores: leaf damage and stalk removal, respectively. In undamaged plants, seasonal increases in leaf nicotine content occurred at a rate of 0.046% leaf dry mass/day. Leaf damage doubled the accumulation rate to 0.086-0.138% leaf dry mass/day, while stalk removal resulted in a quadrupling of the accumulation rate to 0.206% leaf dry mass/day. These damage-induced increases in nicotine accumulation are significantly larger than between-plant and phenological variations. Leaf damage to the nornicotine-(N. repanda and N. trigonophylla) and anabasine-accumulating (N. glauca) Nicotiana species native to North America resulted in 1.5- to 5-fold increases in their principal leaf alkaloid pools. We conclude that alkaloid induction is not limited to nicotine-accumulating Nicotiana species and that herbivores feeding on previously damaged plants are likely to encounter tissues with alkaloid titers significantly higher than those of undamaged plants.