Plant roots sense light

Even a child knows that plants need light, and use it to make energy. But scientists writing in the latest edition of the journal PNAS have shown that the roots of plants might also sense light - or at least a form of ultraviolet light called UVB.

It's all down to a gene called RUS1, which measures UVB light levels and passes the information on to other parts of the plant responsible for growth. So if there's low levels of UVB, for example is the plant is growing in low light levels, or under fluorescent lights, then the gene sends signals telling it to grow. In fact, too much UV light can be toxic to many plants.

The scientists, who were based in San Francisco and Washington, found that if the RUS1 gene was faulty, then plants became over-sensitive to UV light, they were stunted and didn't grow leaves even in low levels of UV light, which should have been good for growth.

It may seem strange that roots, which are usually underground, would respond to light, but in fact UV light - and the RUS1 gene - seem to be most important when a plant is a young seedling, when its roots are resting on the surface of the soil. And later in a plant's life, its roots can be exposed by the rain, by earth movements, or by animals.

This is just the first step to discovering the genes that control the way that plants respond to ultraviolet light. Now scientists have found RUS1, it's likely that they'll be able to track down more genes in the pathway, which will tell us a lot more about the way in which plants develop, and how they respond to light.