The capacity for continued growth allows plants to respond to changes in their environment by growing more in one direction than another. To respond in a manner that enhances fitness, however, plants must first gain information about the world around them. Plants rely on three types of sensory receptors: Photoreceptors sense the availability of light needed to drive photosynthesis; mechanical receptors sense physical influences such as gravity and wind; and chemical receptors detect the presence of specific chemicals, as well as chemical gradients.

We saw in Chapter 9 how a signal can be conveyed to a cell by a change in the shape of a receptor molecule on the cell surface or within the cell. Sensory receptors in plants work in a similar manner. For example, the absorption of light by a photoreceptor changes the chemical properties of the photoreceptor, similar to the photoreceptors in your eye. When a plant’s sensory receptor is activated, it produces a signal that triggers changes in the cell’s metabolism or alters patterns of gene expression. Hormones play a key role in translating information gained by the plant’s sensory receptors into an appropriate developmental response.