katiesommer, the short answer is "No!"
BUT
Individual parts of "toxic" plants can contain a higher concentration of the "toxic" compound. e.g. leaves and young branches of Prunus caroliniana. (a cyanide compound).
The stage of maturity can have an effect. e.g. ackee (Blighia sapida can be safely consumed only when quite ripe.
The toxic element in Cassava (Manihot esculenta), is destroyed by cooking.
Then there is a person's individual reaction to the effect. Some people are more susceptible to the same dose/exposure to a toxin.