For the first time, scientists have directly observed a phenomenon in living vascular plants that has long been debated in plant physiology: the true reversal of xylem embolism, a key factor enabling some plants to recover rapidly from extended periods of drought. This groundbreaking discovery, made by a collaborative team from Colorado State University (CSU), University of Colorado (CU), and the U.S. Department of Agriculture (USDA), could have transformative implications for agriculture, particularly in enhancing drought resilience and securing global food production under intensifying climate stressors.
Drought is an increasingly common challenge worldwide, imposing severe constraints on agricultural systems and directly impacting both crop yield and economic stability. In the United States, drought-associated losses run into billions of dollars annually, not only from diminished harvests but also due to increased water demands and irrigation costs. Central to a plant’s ability to endure water scarcity is its hydraulic architecture, wherein the xylem vessels act as conduits for water transport from roots to photosynthetic tissues. When plants desiccate, air bubbles—known as embolisms—form within these tiny vessels, obstructing the flow of water and threatening the plant’s own survival.
Historically, the process by which plants might restore water flow post-drought, called “embolism refilling,” has been controversial and elusive in intact plants. Most previous evidence supporting refilling came from destructive laboratory techniques that involve cutting plant tissues and artificially pressurizing them to restore water flow—a method now regarded as prone to generating artifacts. These procedures can inadvertently induce embolism formation or misrepresent natural refilling dynamics, casting doubt on prior conclusions.
To circumvent these methodological pitfalls, the research team employed an advanced micro-computed tomography (micro-CT) scanner originally developed for biomedical imaging. This specialized X-ray technology enables non-invasive, time-resolved visualization of the internal state of plant tissues under natural conditions, providing unprecedented insight into the progression and reversal of embolisms within live specimens. The micro-CT’s low radiation emission also allowed repeated scans without compromising plant health, crucial for monitoring dynamic physiological changes over time.
Their study focused on a hardy wild grass species growing resiliently in the cracks of a hot, sun-baked asphalt parking lot, providing a real-world test subject for prolonged drought stress. Despite exhibiting as much as 88% embolized xylem following a sustained period without water, this grass was found to execute a complete reversal of embolism within 24 hours after re-watering, restoring full hydraulic function and vitality. This rapid “resurrection” of the plant’s water transport network marks the first unequivocal demonstration of embolism refilling in vascular plants, confirming a physiological mechanism once thought improbable.
Lead author Jared Stewart, along with CSU and CU collaborators, carefully documented this phenomenon using the high-resolution images captured by the micro-CT scanner. Their observations revealed that the gas bubbles previously clogging the xylem were effectively removed, allowing water to reflood the vessels and re-establish continuous transport pathways. Co-author Sean Gleason of the USDA Agricultural Research Service noted that this represents a paradigm shift, establishing refilling not as a laboratory artifact but as a genuine biological process capable of restoring plant hydraulic integrity in situ.
The implications of this discovery extend far beyond plant physiology. Understanding the genetic and biochemical bases of embolism refilling could open new avenues for crop improvement, enabling breeders to develop drought-resilient varieties by harnessing or introducing this trait through selective breeding or genetic engineering. If widely present among other species, such a mechanism could increase agricultural sustainability by reducing reliance on irrigation and mitigating yield losses under drought conditions.
While this is currently the only plant species known to exhibit rapid embolism reversal, researchers are optimistic that similar traits exist in other taxa. Co-author Troy Ocheltree from CSU emphasized the need for further surveys and genetic analyses to establish the prevalence and mechanistic diversity of refilling across plant lineages. Such knowledge could redefine our understanding of plant resilience and reshape agricultural management practices worldwide.
The success of this study hinged on a unique interdisciplinary collaboration between plant scientists and biomedical imaging experts. CSU’s College of Veterinary Medicine and Biomedical Sciences provided access to the micro-CT infrastructure, originally designed for small animal studies. The device’s low radiation output was integral to carrying out frequent scans over time without harming the plants, enabling the real-time monitoring crucial for capturing embolism dynamics.
Special thanks were extended to Professor Nicole Ehrhart and lab technician Laura Chubb for their support and expertise in operating the micro-CT scanner, illustrating the power of cross-disciplinary cooperation in scientific discovery. Ehrhart highlighted how adapting biomedical technology for plant research yielded innovative insights, demonstrating the versatile applicability of imaging tools beyond their traditional domains.
Despite this monumental breakthrough, many questions remain. Future research will focus on elucidating the biochemical pathways and cellular mechanisms underlying embolism refilling. Determining whether active metabolic processes or physical forces drive the removal of gas bubbles remains a critical next step. Additionally, investigating how environmental factors influence refilling capacity will be vital for translating laboratory findings into agricultural practice.
This research not only enhances fundamental understanding of plant hydrodynamics but also contributes to the broader efforts aimed at combating food insecurity and adapting agriculture to climate change. With drought events predicted to increase in frequency and severity, unlocking the secrets of plant resilience mechanisms such as embolism refilling could prove crucial in sustaining food production and ecosystem health.
As scientists continue exploring the genetic foundations of this refilling trait, there is hope that future crop varieties might be engineered or bred to recover rapidly from drought-induced stress, thereby improving yield stability. Such innovations hold the promise of more efficient water use, potentially reducing irrigation demands and preserving vital freshwater resources in drought-prone regions around the globe.
In sum, the pioneering work by researchers at CSU, CU, and USDA not only settles a longstanding debate in plant science but also charts a new course toward resilient agriculture. Employing cutting-edge imaging technology allowed them to witness, for the first time, the living process of xylem embolism reversal. This not only deepens scientific knowledge but sparks exciting possibilities for future applications aimed at addressing some of the most pressing challenges in agriculture and environmental sustainability.
Subject of Research:
Plant physiology and hydraulics; xylem embolism and refilling in vascular plants.
Article Title:
Xylem embolism refilling revealed in stems of a weedy grass.
News Publication Date:
20-Mar-2025.
Web References:
Proceedings of the National Academy of Sciences article
USDA ARS press release
References:
Stewart J.R., Allen B., Polutchko S., Gleason S., Ocheltree T.W., et al. (2025). Xylem embolism refilling revealed in stems of a weedy grass. Proceedings of the National Academy of Sciences, DOI:10.1073/pnas.2420618122.
Image Credits:
John Eisele/Colorado State University
Keywords:
Plants, Plant anatomy, Plant sciences, Plant breeding, Horticulture, Crop domestication, Agronomy, Plant development, Plant defenses, Plant genetics, Plant growth, Plant life cycles, Plant stresses, Plant physiology, Agriculture, Agricultural engineering, Farming, Sustainable agriculture, Food security, Food resources, Droughts, Food crops, Food production, Grasses, Computerized axial tomography, Medical imaging, Clinical imaging
