Plants have fascinated scientists for centuries. They sort of act like animals, but they’re clearly different. How many similarities do they share with humans? Can they see? In 1907, the son of Charles Darwin believed that they might be able to. Francis Darwin suggested they had organs comprised of light-sensitive and “lens” cells that drew plants to life-giving light, and experiments did seem to suggest the existence of these “ocelli,” but it wasn’t until recently that more progress was made.
Plants have photoreceptors on their leaves and stems that are pretty complex. They can distinguish between red, blue, and even ultraviolet light. They can figure out what direction the light is coming from – ever noticed how plants bend towards a light source? – and how bright that light is. One of these photoreceptors is called a phytochrome, which detects red light. If exposed to red light, it becomes increasingly sensitive so it can detect “far-red light,” which is the most extreme red on the visible spectrum. Phytochromes allow plants to speed up their growth when they have a lot of sunlight. Phototropins manage a plant’s “vision” of blue light.
Studying phytochromes and phototropins doesn’t really answer the question about whether plants can “see” like mammals. The receptors are totally different from what can be found in an animal eye, but they do all share one photoreceptor called a cryptochrome. It detects blue and UV light and essentially acts like a clock that regulates the plant. In animals, this receptor sets circadian rhythms. So, we aren’t entirely different from plants.
2016 saw the discovery of single-celled organisms that, like plants, use photosynthesis. These little guys also behave like ocelli and use their entire bodies as a lens to focus on a light source. A microbiologist from the University of London compared it to the retina of an animal’s eye. This is the closest scientists have gotten to figuring out if plants can see, and it’s very exciting to the community. Something else that’s interesting about the question if plants can see is that certain plants have at least 11 photoreceptors, while humans only have four. This could mean that plants actually “see” better than we do!