Research reveals how plant roots sense light

A recent study published in Science-Signals showed that plants appear to direct sunlight to underground roots to help them grow.

It is well-known that photoreceptors in stems, leaves and flowers regulate plant growth. Although these receptors are also present in the roots, it is still not clear how they perceive light in the depths of the dark soil.

Hyo-Jun Lee from Seoul National University in South Korea and colleagues studied the phenomenon using a small flowering plant from the family Brassicaceae, Arabidopsis, as a model. They found that the stem of Arabidopsis functions like a fiber optic cable, directing light down to the root receptors known as phytochromes. This triggers the production of a protein called HY5 to promote healthy root growth.

▲ perceives light in darkness

When these plants were transformed to possess a phytochrome mutation, HY5 production began to decline. And when they have the HY5 mutation, the root growth is hampered and stretched very strangely.

To confirm that the light is being transmitted directly in the plant instead of activating the signal chemicals that travel to the roots, the researchers connected a light source to the plant stem via fiber optics. The ground-based detector at the end of the root confirms that light is transmitted directly there.

More importantly, no significant increase in root growth was observed when they treated dark-colored Arabidopsis samples with common plant signaling chemicals such as sucrose. This shows that such chemicals do not drive growth.

The study also found that red light is most efficient at moving plants. Lee said that the long wavelengths of such light may be advantageous because they can travel farther than the shorter blue and green wavelengths. He also said that most plants have phytochromes and this suggests that direct delivery of light through the stem to the roots is a common mechanism that is being used to optimize root growth.