The reaction of the plant or plant part to red light.
Source:GO:0009639
Comment
Any process that results in a change in state or activity of a plant part or cell (in terms of movement, secretion, enzyme production, gene expression, etc.) as a result of a red or far red light stimulus. Red light is electromagnetic radiation of wavelength of 580-700nm. Far red light is electromagnetic radiation of wavelength 700-800nm.