A study published in Nature by a joint EPFL and University of Lausanne team describes a defense mechanism in plants to cope with salt stress, opening up new research opportunities to improve food security.
The CryoNanoSIMS instrument enables chemical imaging of biological tissues with a resolution of 100 nanometers. Image credit: © Alain Herzog / EPFL – CC-BY-SA 4.0
According to the United Nations, soil salinization, which affects 20-40% of fertile soils worldwide, is primarily due to human activities and climate change, including sea-level rise. Unlike humans, most plants do not require sodium to function properly. Too much salt around plant roots reduces water availability, slows growth, harms plants and causes premature plant death. Soil salinization causes the loss of 10 million hectares of farmland every year, posing a serious threat to global food security.
Researchers from EPFL, the University of Lausanne (UNIL) and collaborators in Spain studied “Salt Overly Sensitive 1” (SOS1), a gene discovered in 1996 that protects plant cells from salt stress. Using a unique microscopic ion probe, CryoNanoSIMS (Cryo Nanoscale Secondary Ion Mass Spectrometry), the team created a detailed picture of nutrient storage and utilization in cells and tissues.
Their findings show that under significant salt stress, the ion transporter SOS1 promotes sodium uptake into the cell vacuole rather than exporting it, an adaptation that helps minimize the toxic effects of excess salt inside plant cells.
The researchers say that better understanding this mechanism and gaining insight into why some species are more tolerant to sodium could contribute to the development of strategies to improve food security.
First visual evidence
Our study provides the first visual evidence at a cellular level of how plants protect themselves from excess sodium.
Priya Ramakrishna, lead study author and postdoctoral researcher at EPFL’s Biogeochemistry Laboratory
“Previous hypotheses about this mechanism were based on indirect evidence,” she added. “We can now see where sodium is transported under different levels of salt stress, which has not been possible with this resolution before. “
The EPFL and UNIL team carried out extremely detailed observations using a newly developed CryoNanoSIMS instrument, which allows chemical imaging of biological tissues with a resolution of 100 nanometers. In this study, plant root samples were rapidly frozen in liquid nitrogen and kept at ultra-low temperatures under vacuum conditions to preserve the elemental composition within the tissue.
This method enabled researchers to map individual plant cells and pinpoint where key elements such as potassium, magnesium, calcium and sodium are stored in the root apical meristem – the region that contains the stem cells responsible for the development of the root system. CryoNanoSIMS imaging provides detailed information about the state of root cells under two different salt stress conditions.
Change in strategy
The team found that under high salt stress, the SOS1 transporter sequesters sodium in the vacuole, an organelle that stores unwanted compounds, rather than exporting it as previously thought. Under mild salt stress, cells can completely block sodium entry.
” However, this defense mechanism consumes energy, slows down plant growth, inhibits plant function and ultimately leads to plant death if salt stress persists ,” explains Ramakrishna.
The researchers performed similar tests on mutant samples lacking the SOS1 transporter gene and confirmed their findings. These mutants had increased sensitivity to salt stress, and the researchers concluded that this was due to an inability to transport sodium to the vacuole. Testing root samples from rice, the world’s most widely cultivated crop, showed a similar pattern: under extreme salt stress conditions, sodium was translocated to the vacuole.
Location fit function
For Ramakrishna, a plant biologist by training, the chemical imaging tool CryoNanoSIMS was revolutionary: it could also be used to study how plants defend themselves against other hazards, such as microbes or heavy metal pollution.
This truly interdisciplinary collaboration – combining biology and engineering – allows us to combine location and function and understand mechanisms and processes never before observed.
Anders Meibom, corresponding author of the study and professor in the Department of Architecture, Civil and Environmental Engineering at EPFL
He also works at UNIL’s Department of Earth and Environmental Sciences, where the CryoNanoSIMS instrument was developed.
Nico Goeldner, corresponding author of the study, Director of the UNIL Research Group at the School of Biological Sciences and Medicine and Head of the UNIL Group, is also excited about the collaboration.
Plants are fundamentally dependent on extracting mineral nutrients from the soil, but until now it has not been possible to observe their transport and accumulation with sufficient resolution. CryoNanoSIMS technology has finally achieved this and promises to transform our understanding of plant nutrition beyond the issue of salt.
Nico Goeldner, corresponding author and dean of the School of Biological and Medical Sciences, University of Lausanne
“This technique opens up entirely new horizons in the field of biological tissue imaging, making our institution a leader in this field , ” added Professor Christelle Genoud, co-author of the study and director of the Dubochet Diagnostic Imaging Center.
Journal References:
Ramakrishna, K. et al. (2025) Elemental cryoimaging reveals SOS1-dependent vacuolar sodium accumulation. Nature . doi.org/10.1038/s41586-024-08403-y
