Plant Photoreceptors: Definition, Types & Function

Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Can plants tell time? How do they know when it's sunny out? Photoreceptors are specialized cells that communicate this information to plants, which in turn helps them know when to make energy from sunlight as well as when and how to grow.


Plants depend on light for a variety of reasons. Most importantly, they need it to photosynthesize, or convert sunlight into energy. Light stimulates growth and development in plants as well, and the amount of light a plant receives also allows them to measure passing days and seasons.

But how do plants perceive light? Plants have photoreceptors, which are proteins that are specially designed to perceive light and signal certain biological effects in the plant. The effect of light on plant morphology (the form and structure of something) is called photomorphogenesis.

To understand photoreceptors, you need to know a little about light. Our eyes see what is called visible light. This light travels in waves, and when we see colors, we are actually seeing certain waves of light being reflected off of objects. For example, a blue car sends blue light to our eyes and absorbs the other light waves. Likewise, green grass reflects green light to our eyes, so we see green because the grass is absorbing the other colors.

What does this have to do with plants? Well, being able to detect different waves of light is important to plants, because they use the different light waves for different purposes.

Types and Functions

Plants have two different types of photoreceptors to perceive different waves of light: blue-light receptors (those that absorb blue light waves) and phytochromes (those that absorb red light waves).

Blue light signals a variety of effects in plants. For example, phototropism, the growth of a plant toward light, is signaled by blue light. Phototropism is a mechanism that helps plants get as much sunlight as possible. A hormone called auxin is produced that makes one side of the plant grow faster than the other, which bends it toward the light source. Blue light also triggers a plant's stomata to open. Stomata are pores on plant leaves that facilitate gas exchange during photosynthesis.

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