You might already know that the stems, leaves and flowers of plants have light receptors in them that control their growth, including the direction in which they grow. (The latter phenomenon is called phototropism.)

But plants also have light receptors in their underground root systems. For a long time, it hasn't been clear how these biological sensors detect light, considering that they're buried in soil, where you'd think that they would be immersed in darkness.

Amazingly, though, according to new research published in the journal Science Signaling, plants actually have a way of "seeing" underground.

Scientists at Seoul National University in South Korea studied a small flowering plant called Arabidopsis thaliana, which is part of the mustard family and related to cabbage and radish.

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They found that the plant's stem conducted light down through itself to the light receptors in its root system. The stem essentially turned itself into a biological version of a fiber-optic cable, as a New Scientist article on the research noted.

That transmission was important, because they told the plant to produce a protein called HY5 that promotes growth of its roots. When plants were genetically engineered so that the light receptors in the roots didn't work, their roots were stunted.

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"These findings demonstrate that roots not only receive information about light conditions through signaling molecules that travel from the shoot to the root in response to light but also directly perceive light that is conducted through the plant tissues," the scientists concluded in their study.

Most plants have light receptors in their roots, so they probably use the same sort of signaling system, Mike Haydon, a scientist at the University of Melbourne in Australia, explained to New Scientist.

Transmitting information via light is more advantageous than chemical transmission, because it's a lot faster.

Arabidopsis thaliana plants have a system for transmitting information about light to receptors in their root systems. Credit: Stefan.lefnaer via Wikimedia Commons

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