Plants thirst for water, just as we animals do, but exactly how they slurp it through their tissues has remained a bit of a mystery as attempting to see it happening impairs the process.

By applying a gentle imaging technique in a new way, University of Nottingham physicist Flavius Pascut and the team were able to watch plants' innards at work as they drank in real time.

"We've developed a way to allow ourselves to watch that process at the level of single cells," said University of Nottingham electrophysiologist Kevin Webb. "We can not only see the water going up inside the root, but also where and how it travels around."

Not only is the water itself essential to the plants, it also acts as a vehicle for transporting other nutrients, minerals, and important biomolecules throughout the living structures. How efficiently plants are able to move the precious liquid around can have a huge effect on their ability to tolerate harsh environmental conditions.

"To observe water uptake in living plants without damaging them, we have applied a sensitive, laser-based, optical microscopy technique to see water movement inside living roots non-invasively, which has never been done before," explained Webb.

By detecting how light photons scatter from a narrow laser source, Raman microspectroscopy provides real time, molecular level imaging, under natural conditions, without the need for molecular labeling.

This technique is so sensitive that it can detect the mass and orientation of molecular bonds. This means that contrast can be provided by using molecules that stand out from their surroundings – in this case, deuterium oxide, known as heavy water, in place of normal water. Deuterium is an isotope of hydrogen that has a neutron as well as normal hydrogen's usual lone proton, doubling its mass.

While heavy water has slightly different properties, it's similar enough to normal water not to change things physiologically in small amounts.

The scan detected a pulse of the heavy water within 80 seconds of exposing the roots of researchers' most thoroughly studied plant, thale cress (Arabidopsis thaliana). Pascut and the team alternated between exposing the flowering plant to normal water and heavy water to watch how new water moved through the plant tissues.

Curiously, researchers only detected the sucked-up water in the inner part of the roots, where the water transporting root tissues xylem occurs, showing this initial water uptake is not shared to surrounding tissues on its way up from the roots to the rest of the plant.

The researchers think this means that there are "two water worlds" within the plant and that the second system of water diffusion distributes water to these outer tissues.

Being able to observe this process will help us understand it and better plan crops for the tumultuous future we're facing.

"The goal is to increase global food productivity by understanding and using plant varieties with the best chances of survival that can be most productive in any given environment, no matter how dry or wet," said Webb.

Pascut and the team are developing a portable version of the imaging technology to allow for more accessible field studies, and they also believe this technique could be used in healthcare monitoring devices, although our cells are much smaller than plants'.

For now, though, "this promises to help us address important questions such as – how do plants 'sense' water availability?" explained University of Nottingham plant scientist Malcolm Bennett.

"Answers to this question are vital for designing future crops better adapted to the challenges we face with climate change and altered weather patterns."

This research was published in Nature Communications.