Reviewed by Lexie CornerJan 16 2025
A study published in Nature by a joint research team from EPFL and the University of Lausanne research team describes a plant defense mechanism in response to salt stress, presenting new research opportunities to improve food security.
The CryoNanoSIMS instrument permits obtaining chemical images of biological tissue at a resolution of 100 nanometers. Image Credit: © Alain Herzog / EPFL - CC-BY-SA 4.0
According to the United Nations, soil salinization, which affects 20 % to 40 % of fertile land globally, is largely driven by human activities and climate change, including rising sea levels. Unlike humans, most plants do not require sodium for normal functioning. Excess salt around plant roots reduces water availability, stunting growth, damaging the plant, and accelerating its death. Soil salinization results in the loss of ten million hectares of farmland annually, posing a serious threat to global food security.
Researchers from EPFL, the University of Lausanne (UNIL), and Spanish collaborators investigated the 1996-discovered gene "Salt Overly Sensitive 1" (SOS1), which protects plant cells from salt stress. Using CryoNanoSIMS (Cryo Nanoscale Secondary Ion Mass Spectrometry), a unique ion microprobe, the team generated detailed images of nutrient storage and utilization within cells and tissues.
Their findings indicate that under significant salt stress, the SOS1 ion transporter facilitates the loading of sodium into the cell's vacuoles rather than expelling it. This adaptation helps mitigate the toxic effects of excess salt within plant cells.
The researchers suggest that a deeper understanding of this mechanism, along with insights into why some species exhibit greater sodium tolerance, could contribute to developing strategies for improving food security.
First Visual Proof
Our research provides the first visual proof, at the cellular scale, of how plants protect themselves against excess of sodium.
Priya Ramakrishna, Study Lead Author and Postdoctoral Researcher, Laboratory for Biological Geochemistry, EPFL
She added, “Previous hypotheses of this mechanism were based on indirect evidence. We can now see where sodium is transported to at different levels of salt stress – something we were unable to do at this resolution before.”
The EPFL and UNIL team conducted highly detailed observations using the recently developed CryoNanoSIMS instrument, which enables chemical imaging of biological tissue at a resolution of 100 nanometers. In this study, plant root samples were snap-frozen in liquid nitrogen and maintained at extremely low temperatures under vacuum to preserve the elemental composition within the tissue.
This approach allowed the researchers to map individual plant cells and identify the storage locations of key elements such as potassium, magnesium, calcium, and sodium within the root apical meristem, the region containing stem cells responsible for root system development. CryoNanoSIMS imaging provided insights into the status of root cells under two distinct salt stress conditions.
A Change of Strategy
The team discovered that under high salt stress, the SOS1 transporter sequesters sodium into vacuoles—organelles that store unwanted compounds—rather than expelling it, as previously believed. Under mild salt stress, cells can block sodium entry entirely.
“But this defense mechanism is energy-intensive, slowing down the plant’s growth, inhibiting its performance, and ultimately leading to its death if the salt stress persists,” explained Ramakrishna.
The researchers confirmed their findings by conducting the same tests on mutant samples lacking the SOS1 transporter gene. These mutants displayed heightened sensitivity to salt stress, which the researchers attributed to their inability to transport sodium into vacuoles. Tests on rice root samples, representing the world’s most widely cultivated crop, showed a similar pattern: sodium was transferred to vacuoles under extreme salt stress.
Matching Location with Function
For Ramakrishna, who is trained as a plant biologist, the CryoNanoSIMS instrument's chemical imaging is revolutionary. Additionally, the tool might be used to study how plants defend themselves against additional dangers like microorganisms and heavy metal pollution.
With this kind of truly interdisciplinary collaboration, i.e., blending biology and engineering, we can match location with function and understand mechanisms and processes that have never been observed before.
Anders Meibom, Study Corresponding Author and Professor, School of Architecture, Civil and Environmental Engineering, EPFL
He also works at UNIL’s Faculty of Geosciences and Environment, where the CryoNanoSIMS equipment was developed.
Niko Geldner, the study’s co-corresponding author, director of the research team at UNIL’s Faculty of Biology and Medicine, and leader of the UNIL team, is also excited about this collaboration.
Plants are fundamentally dependent on extracting mineral nutrients from the soil, but we were never able to observe their transport and accumulation at sufficient resolution. The CryoNanoSIMS technology finally achieves this and promises to transform our understanding of plant nutrition, beyond the problem of salt.
Niko Geldner, Study Corresponding Author and Director, Faculty of Biology and Medicine, University of Lausanne
Professor Christel Genoud, co-author of the study and Director of the Dubochet Center for Imaging, added, “This technique is opening up an entirely new horizon in the imaging of biological tissue and places our institutions as leaders on this frontier.”
Journal Reference:
Ramakrishna, K. et. al. (2025) Elemental cryo-imaging reveals SOS1-dependent vacuolar sodium accumulation. Nature. doi.org/10.1038/s41586-024-08403-y