NEUROTRANSMITTERS IN PLANTS. “Plant and animal cells and tissues share a number of ‘neural’ similarities. To name some of them, glutamate, dopamine, serotonin, and other neurotransmitters are found in plants, although their function still needs to be clarified (auxin can be identified as the plant-specific neurotransmitter for the purpose of signaling.”
http://link.springer.com/article/10.1007/s11229-016-1040-1