A number of structurally related isoquinoline alkaloids also are found in this and related plants. Although the compound looks simple, the biosynthetic pathway leading to it is complex. Both gramine and hordenine appear to be allelopathic agents in field situations. Psilocybin occurs in a number of fungi, but is best known from Psilocybe species. These mushrooms are common in southern Mexico.
Pyridine alkaloids One of the best pyridine alkaloids is nicotine.
In tobacco plants, this alkaloid is synthesized from nicotinic acid and ornithine. Nicotinic acid in plants is synthesized from a different pathway from that in animals. A 60 day old tobacco plant contains about 250 mg of nicotine. The half life of nicotine in tobacco plants is about 22 hours. Approximately 40-60 mg of nicotine is a lethal dose for an adult human.