Serotonin - in Plants

In Plants

In drying seeds, serotonin production is a way to get rid of the buildup of poisonous ammonia. The ammonia is collected and placed in the indole part of -tryptophan, which is then decarboxylated by tryptophan decarboxylase to give tryptamine, which is then hydroxylated by a cytochrome P450 monooxygenase, yielding serotonin.

However, since serotonin is a major gastrointestinal tract modulator, it may be produced by plants in fruits as a way of speeding the passage of seeds through the digestive tract, in the same way as many well-known seed and fruit associated laxatives. Serotonin is found in mushrooms, fruits and vegetables. The highest values of 25–400 mg/kg have been found in nuts of the walnut (Juglans) and hickory (Carya) genera. Serotonin concentrations of 3–30 mg/kg have been found in plantains, pineapples, banana, kiwifruit, plums, and tomatoes. Moderate levels from 0.1–3 mg/kg have been found in a wide range of tested vegetables.

Serotonin is one compound of the poison contained in stinging nettles (Urtica dioica), where it causes pain on injection in the same manner as its presence in insect venoms (see above). It is also naturally found in Paramuricea clavata, or the Red Sea Fan.

Serotonin and tryptophan have been found in chocolate with varying cocoa contents. The highest serotonin content (2.93 ug g-1) was found in chocolate with 85% cocoa, and the highest tryptophan content (13.27-13.34 ug g-1) was found in 70-85% cocoa. The intermediate in the synthesis from tryptophan to serotonin, 5-hydroxytryptophan, was not found.

Unlike its precursors, 5-HTP and tryptophan, serotonin does not cross the blood–brain barrier, which means ingesting serotonin in the diet has no effect on brain serotonin levels.