Although plants have no nervous system or sense organs, they have sensitive receptor molecules and cells that detect stimuli. A detected signal is converted (transduced) into a chemical signal, such as a change in the concentration of calcium ions or of a plant growth regulator, which then alters gene expression or growth.Detecting lightPlants have several types of photoreceptor pigment:- Phytochromes absorb red and far-red light. They let the plant detect whether it is light or dark, how long the night is, and whether it is shaded by other plants.
- Phototropins absorb blue light. They detect the direction of light and control phototropism and stomatal opening.
- Cryptochromes also absorb blue light and help regulate growth and the daily (circadian) rhythm.Detecting gravityCells in the root cap contain statoliths: dense amyloplasts (starch-filled plastids) that settle to the lower side of the cells. Their position tells the root which way is down and leads to auxin being redistributed.Detecting touch and damageMechanical stimuli such as touch or wind open ion channels in cell membranes. Damage by herbivores triggers chemical signals that switch on the production of defensive chemicals, sometimes in leaves far from the damaged site.These sensory systems let plants monitor their environment continuously and adjust their growth, flowering and defences. Because the responses usually involve changes in gene expression and growth, they are slower than nervous responses in animals.
- Phototropins absorb blue light. They detect the direction of light and control phototropism and stomatal opening.
- Cryptochromes also absorb blue light and help regulate growth and the daily (circadian) rhythm.Detecting gravityCells in the root cap contain statoliths: dense amyloplasts (starch-filled plastids) that settle to the lower side of the cells. Their position tells the root which way is down and leads to auxin being redistributed.Detecting touch and damageMechanical stimuli such as touch or wind open ion channels in cell membranes. Damage by herbivores triggers chemical signals that switch on the production of defensive chemicals, sometimes in leaves far from the damaged site.These sensory systems let plants monitor their environment continuously and adjust their growth, flowering and defences. Because the responses usually involve changes in gene expression and growth, they are slower than nervous responses in animals.