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'Resurrection' millet—a plant that revives after severe drought

A new discovery by scientists could help protect crop production and reduce plant mortality due to drought, which accounts for a quarter of U.S. crop production losses.

Water is essential for plants to grow, reproduce, and survive. Drought causes severe stress in plants and can significantly reduce yearly production or kill entire crops. Drought also increases costs for farmers, who must invest in irrigation to keep their crops alive. These impacts and costs result in reduced food supply and higher food prices for consumers.

After years of studying the mechanisms and effects of drought in plants, scientists at the USDA's Agricultural Research Service (ARS) and Colorado State University (CSU) identified how plants die during drought and how some of the effects of drought can be reversed. They also discovered a plant species (a wild millet relative) with remarkable resiliency to extreme drought, demonstrating an ability to "resurrect" after acute drought episodes. The work is in the Proceedings of the National Academy of Sciences.

During severe drought stress, the soil and atmosphere become so arid that liquid water inside the plant changes into water vapor gas. This process, known as embolism formation, results in gas bubble blockages within the water-conducting tissues of the plant. These embolism blockages reduce the transport of water and minerals from the soil [roots] to the leaves, impairing essential processes for the growth, reproduction, and survival of plants.

Embolism formation was poorly understood in plants because embolisms could not be seen using the types of instrumentation and methodology used in past studies. The team of scientists at ARS and CSU used an innovative method that involved scanning entire plants with a type of laboratory X-ray machine. The machine allowed them to see water movement through segments of the plant, including stems, roots, and leaves, which enabled the scientists to detect these gas bubble formations, or embolisms, throughout the plant.

"We have discovered that a wild millet relative is capable of reversing embolism formation in the water-conducting tissues," said Sean Gleason, ARS research plant physiologist at the Water Management and Systems Research Unit in CO. "We call this plant resurrection millet because if the plant is watered even after nearly 100% of the tissue has been embolized, the plant is able to re-fill these embolisms and recover.

"This study provides the first direct evidence of complete and functional stem xylem 'refilling' following severe drought stress. This breakthrough challenges long-standing assumptions about plant hydraulic recovery and has significant implications for crop resilience in water-limited environments."

Troy Ocheltree, a co-author and collaborator with the CSU Department of Forest and Rangeland Stewardship, explained the important implications this study has for both crop improvement and natural grasslands.

"The results suggest that even if plants become severely stressed, they may be able to recover in the same year of the drought and begin growing again," he said. "This ability impacts the yield of crop production and the amount of forage available for cattle."

Researchers seek to leverage new technology to transfer the resiliency found in this millet species to other crop species such as wheat, corn, and rice, thus protecting U.S. agriculture.