Humans have about 400 odor receptors. Elephants have about 2,000, the largest number in animals. But based on how many transcription factor genes are in plants, plants may be able to detect many more odors than animals.
— Professor Kazushige Touhara, whose team at the University of Tokyo "have discovered the first steps of how information from odor molecules changes gene expression in plants". Read more at Plants can smell, now researchers know how at ScienceDaily.