A plant hormone that accelerates root growth could be a new farming tool

A molecule sold as a food additive also plays an underground role: it helps the roots grow faster.

When added to the soil, the molecule, called beta-cyclocitral, accelerates root growth in rice and tomato plants, scientists report on May 8, 2019, in the newspaper. Proceedings of the National Academy of Sciences. It also makes rice plants resistant to salty soil, which usually makes them sick and stunted. The molecule, a naturally occurring hormone found in plants, could be a useful tool for farmers looking for healthier and more drought-resistant crops.

For centuries, plants have been selected for their vigorous foliage and other easily visible features. As the roots are hidden underground, "they have been largely ignored," said Philip Benfey, a developmental biologist and researcher at the Howard Hughes Medical Institute at Duke University.

And yet, roots represent half of the plant, says co-author Jazz Dickinson, also at Duke. She and Benfey wanted to find plant hormones that affected root development. Their previous research had hinted that a molecule chemically linked to carotenoids – the pigments that give carrots their dazzling orange hue – might be important. But the researchers did not know exactly which one, Dickinson said.

Many of these carotenoid parents have been reused and are available commercially as food additives or supplements. Dickinson collected about 20 and tested their effects on a common laboratory plant, Arabidopsis. She added each compound to the clear agar gel in which the plants were growing – a configuration allowing her to easily see the roots – and monitored what happened for 10 days.

"The beta-cyclocitral has been demarcated," she says. This allowed the roots to grow faster and to diversify further. And this had the same effect on the rice and tomato plants, showed follow-up tests.

The team noted an even more striking effect in the rice plants: the plants could also withstand salty soil. Irrigation of fields can make the soil more salty, especially near the top. The team imitated these conditions in the laboratory and then observed how the rice plants grew. "The untreated rice plants were very unhappy with this level of salt," says Benfey. But with the beta-cyclocitral added, the plants did not seem disturbed.

It is possible that the compound helped the roots penetrate faster into the salty topsoil to reach deeper and less saline soils faster, suggests Dickinson.

The researchers hope that beta-cyclocitral will be useful in agriculture, added to soil or sprayed on crops. And since the molecule has worked in both rice and tomatoes – two very different plants – it can stimulate root growth in crops more widely.