Plants’ fiber-optic-like stem conducts light from leaves to roots

New Scientist : Plants harvest light by means of photoreceptors in their leaves, flowers, stems, and even roots. But how light reaches the receptors buried underground in a plant’s roots was not known. Now Hyo-Jun Lee of Seoul National University in South Korea and his colleagues have determined that light striking plants from above is directly transmitted to their roots via their stems, which act like fiber-optic cables. The researchers attached a light source to the stems of a small flowering plant in the mustard family, Arabidopsis thaliana, and placed an underground detector at the roots. Not only did the researchers confirm the direct transmission of light, but they also discovered that the system favors the transmission of red light over blue or green. The reason, the scientists say, is that red light’s longer wavelengths allow it to travel farther. Moreover, the lower intensity of red light prevents it from benefiting other creatures or bacteria living in the soil.