Multiple signals regulate nicotine synthesis in tobacco plant.

After wounding of tobacco plants, roots synthesize a large amount of nicotine to be transported to the shoot. Jasmonic acid (JA) acts as a long-distance signal between the wounding stimulus and response in tobacco plants. In addition, another phloem-mobile signal (auxin) plays a role in the transmission of the message triggered by wounding. Auxin can serve as a negative signal to regulate nicotine synthesis in roots of tobacco plants, even when plants are not wounded. Furthermore, removing the shoot apex after girdling the stem base still stimulates nicotine synthesis in roots. Since girdling prevented the involvement of signals transported in the phloem, this wound likely induced a response of nicotine synthesis in roots regulated by a signal transported via an alternative pathway. The results suggest that there are multiple signals in tobacco plant to regulate nicotine synthesis, depending on the treatment.