Fast track to the trichome:: induction of N-acyl nornicotines precedes nicotine induction in Nicotiana repanda

Nicotiana repanda Wildenow ex Lehmann acylates nornicotine in its trichomes to produce N-acylnornicotine (NacNN) alkaloids which are dramatically more toxic than nicotine is to the nicotine-adapted herbivore. Manduca sexta. These NacNNs, like nicotine. were induced by methyl jasmonate (MeJA) and wounding, but the 2-fold increase in NacNN pools was much faster (within 6 h) than the MeJA-induced increase in nornicotine pools (24 h to 4 d), its parent substrate. When (NO3-)-N-15 pulse-chase experiments with intact and induced plants were used to follow the incorporation of N-15 into alkaloids in different plant parts over the plant's lifetime, it was found that the root nicotine Fool was most rapidly labeled, followed by the shoot nornicotine and NacNN pools. After 3 d, 3.12% of N-15 acquired was in nicotine (0.93%), nornicotine (0.32%) and NacNNs (1.73%) while only 0.14% was in anabasine. Once NacNNs are externalized to the leaf surface. they are not readily re-distributed within the plant and are lost with senescing leaves. The woundand MeJA-induced N-acylation of nornicotine is independent of induced changes in nornicotine pools and the rapidity of the response suggests its importance in defense against herbivores.