On a scorching summer day in the American Midwest, farmers aren't the only ones sweating. Corn, sorghum, and other crop plants lose water through tiny pores in their leaves called stomata — and that water loss is a big reason why farming is only possible in places with enough rain.
Now, scientists have taken a major step toward solving this problem. A team at the University of Illinois Urbana-Champaign has created the first detailed three-dimensional map of a sorghum leaf's interior, revealing how air flows through the plant and how water escapes into the atmosphere. The work, published in the journal Plant Physiology, was led by postdoctoral researcher James Fischer in the lab of Professor Andrew Leakey.
"There are connections between each component of the leaf... it's a highly organized system," Fischer said. "We are really defining the leaf beyond just carbon dioxide goes in, water comes out."
The researchers used a powerful imaging technique called micro-computed tomography — the same technology doctors use for CT scans in hospitals, but much stronger. To peer inside a living leaf, they needed X-rays far more powerful than any medical machine can produce. So they turned to Argonne National Laboratory's Advanced Photon Source, a facility that generates intense X-rays as a byproduct of particle physics research.
The team also collaborated with Professor Craig Brodersen at Yale University and Guillaume Théroux-Rancourt of the agricultural research company Biopterre, both experts in using microCT imaging to study plant tissues.
Why does this matter? Plants face a fundamental trade-off. During photosynthesis, they absorb carbon dioxide through their stomata to make food. But for every single carbon dioxide molecule that enters, 300 to 400 water molecules escape. This process, sometimes called "crop sweat," is why agriculture depends on reliable rainfall.
"We're trying to minimize how many water molecules escape while CO2 is going into the leaf to be captured by photosynthesis," said Leakey, who also directs the Center for Advanced Bioenergy and Bioproduct Innovation. His team had already engineered plants with fewer stomata as a proof of concept. Now, thanks to the new 3D maps, they can see exactly how efficiently carbon dioxide travels through the leaf's interior to reach the cells where photosynthesis happens.
When the researchers compared plants with different numbers of stomata, they made an unexpected discovery: leaves with fewer pores had already begun adjusting their internal structures to compensate. "We thought it was something that would be a challenge for us from the engineering perspective..." Fischer said, though the article was cut off before revealing the full finding.
The goal is crops that stay productive in hotter, drier conditions — an increasingly important capability as climate change brings more extreme weather to farming regions around the world. By understanding exactly how a leaf's ventilation system works in three dimensions, scientists can now breed or engineer plants that sweat less while still growing strong.