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How do plants breathe? When do they open and close the tiny pores on their leaves, and what does this mean for their water balance? A research team led by Marburg physicist Professor Martin Koch has developed a method to visualize this process: With the help of terahertz spectroscopy, the scientists can observe when plants open or close their leaf openings (stomata). Their findings have been in the journal Scientific Reports.

Plants absorb carbon dioxide from the air and release oxygen through small structures on the underside of their leaves. With sunlight, the plant converts CO₂ into glucose and loses water. To prevent dehydration, the tiny openings close at night, or even during the day when drought stress prevails. How well plants master this balancing act is crucial for their survival, especially in the face of climate change.

Scientists at Philipps University in Marburg have irradiated plant leaves with terahertz waves. Terahertz waves can be regarded as very long-waved light or very high-frequency microwaves and are strongly absorbed by water. The researchers can deduce the water content of the leaves from the signal attenuation as it passes through the leaf. By comparing the measurement data with a mathematical model, they can deduce when and how far the stomata are open based on the water loss of the leaves.

To test the method, the researchers compared ordinary Arabidopsis plants with variants that are less able to regulate their water balance due to a specific gene mutation. The mutation affects a specific signaling pathway in the plant's drought stress response.

"Using terahertz spectroscopy, we were able to show how manipulating this signaling pathway affects water balance: Plants with genetic defects dry out faster because they are less able to adapt their stomatal opening to the available water supply," explains Jochen Taiber, the study's lead author.

The method enables the investigation of regulatory mechanisms and could help identify crops that are more resistant to climate change in the future.

To enable the method to be used in other laboratories, the group is currently working on making this measurement technology portable and more affordable.