Some of the fruits and vegetables we eat on a regular basis contain some amounts of dopamine. Bananas, potatoes, avocadoes and broccoli to name a few of the plants that naturally have dopamine in them.
Scientists don't really know why these plants have dopamine in them. There is some evidence plants may use it as we do -- to deal with stress. Dopamine may act as a growth promoter in some situation or it may help a plant deal with an infection to the plant. Science can't pin down where the plant receives the stimulus from the dopamine or how the plant activates production.
There is no worry though. Dopamine in plants cannot act on the human brain. The blood-brain barrier, a protective barrier separating circulating blood from the brain, prevents it.