Found this on Wikipedia:Recent research
Recent research has shown that plants can respond to electrical impulses, but their lack of a central nervous system and nociceptive A delta fibers implies that plants have no feeling of pain.[ISBN missing]
The television show MythBusters performed an experiment (Season 2, Episode 5, 2006) to verify or disprove the concept. The tests were done by connecting plants to a polygraph galvanometer and employing actual and imagined harm upon the plants or upon others in the plant's vicinity. The galvanometer showed some kind of reaction about one third of the time. The experimenters, who were in the room with the plant, posited that the vibrations of their actions or the room itself could have affected the polygraph. After isolating the plant the polygraph showed a response slightly less than one third of the time. Later experiments with an EEG failed to detect anything. When the presenters dropped eggs randomly into boiling water the plant had no reaction whatsoever. The show concluded that the results were not repeatable, and that the theory was not true.http://en.wikipedia.org/wiki/Plant_perception_(paranormal
However, I can attest to the fact that plants don't like or respect me. They die in my presence. I even killed a particularly hearty cactus recently. This is probably because the plants know that I am a vegetarian, and that I respect the lives of animals more than I respect their lives.