Imaging Method Reveals the Way Plants Take Up Water

Researchers at the University of Nottingham report the development of a way to observe how plant roots take in and circulate water at the cellular level. The work could help to identify future drought- and flood-resistant crops.

The inability to monitor water uptake inside roots without damaging the specimen has been an obstacle for researchers seeking to understand the motion of fluids in living plant cells and tissues.

An image of the water-filled pore space of wheat roots. Courtesy of the University of Nottingham.

To observe water uptake in living plants without damaging them, Kevin Webb of the Optics and Photonics Research Group and lead on the study, with his team, applied a sensitive, laser-based optical microscopy technique to see water movement inside living roots noninvasively — something never done before, Webb said.

“Fundamentally, the process by which plants are able to thrive and become productive crops is based on how well it can take up water and how well it can manage that process,” Webb said. “Water plays an essential role as a solvent for nutrient, minerals, and other biomolecules in plant tissues. We’ve developed a way to allow ourselves to watch that process at the level of single cells. We can not only see that water that’s going up inside the root, but also where and how it travels around.”

For the study, water transport measurements were performed on the roots of Arabidopsis thaliana, which is a “model plant” for scientists; it can be easily genetically engineered to interfere with basic processes such as water uptake.

The imaging method, based on the Raman-scattering technique, used a low-intensity laser to measure water traveling through the root system at the cellular level. The scientists used a mathematical model to explain and quantify the motion.

The team then used “heavy water” (deuterium oxide), which contains an extra neutron in the nucleus of each hydrogen atom. By scanning a laser in a line across the root while the plant drank, it was possible to see the heavy water moving via the root tip.

In Arabidopsis that had been genetically altered to compromise its water uptake, these measurements, with the mathematical model, revealed a water barrier within the root. This confirmed for the first time that water uptake is restricted within the central tissues of the root, inside of which the water vessels are located.

Graphic representation of the hydrodynamic process using Raman imaging. Courtesy of the University of Nottingham.

Malcolm Bennet, co-lead of the study and professor of plant sciences at the university, said, “This innovative technique is a real game-changer in plant science — enabling researchers to visualize water movement at a cell and second scale within living plant tissue for the very first time. This promises to help us address important questions such as how plants ‘sense’ water availability. Answers to this question are vital for designing future crops better adapted to the challenges we face with climate change and altered weather patterns.”

While developing the method, the research focused initially on plant cells, which are about 10× the size of human cells, and therefore more easily observed. As with plants, there are tissues in the human body that are responsible for handling water, which is crucial to function. Transparent tissues of the eye, for example, can suffer from disease related to fluid handling, such as ocular lens cataracts, macular degeneration, and glaucoma.

The team is currently working to adapt the method to monitor human cells to understand the same type of process at a smaller scale. At the same time, it is working on portable versions of the technology to allow water transport measurements to be taken in the field.

The team is currently bidding for a European Research Council Synergy Grant with partners in the EU and U.K. to take the study of water uptake and drought resistance toward being a new tool to help choose and understand how particular crops can be matched to particular local growth conditions.

The research was published in Nature Communications (www.doi.org/10.1038/s41467-021-24913-z).