Laser microbubbles to test plant cell pressure
Using laser nucleation of microbubbles, physicists have shown that stomata, the miniature 'gates' that regulate light-dependent evaporation in vascular plants, remain inactive in non-vascular plants such as mosses.
References
In-situ cavitation bubble manometry reveals lack of light-activated guard cell turgor modulation in bryophytes, Craig R. Brodersen, Tim Brodribb, Uri Hochberg, N. Michele Holbrook, Scott A. M. McAdam, Joseph Zailaa, Brett Huggett, Philippe Marmottant, Proceedings of the National Academy of Science, Publié le 26 mars 2025
Doi : 10.1073/pnas.2419887122
The water pressure inside plant cells is very high, reaching tens of bar. This 'turgor pressure' helps plants to grow and contributes to their mechanical strength. Its modulation is also closely linked to the opening movements of the stomata, the tens of micrometre wide 'doors' that allow water to evaporate from the leaf surface. The evolution of stomata has been one of the main driving forces behind the radical changes in the Earth's atmosphere over the last 400 million years, giving plants the ability to regulate their water loss and optimise photosynthesis. Modulation of stomatal turgor pressure was a key innovation that may have been specific to vascular plant lineages..
This research was carried out in the following CNRS laboratory:
- Laboratoire interdisciplinaire de physique (LIPhy, CNRS / Université Grenoble Alpes)
However, the pressure in these stomata is difficult to measure using the traditional method of piercing with a micropipette. A collaboration of researchers (USA, Australia, Israel, France), including the Interdisciplinary Physics Laboratory (LIPhy, Grenoble), has developed a new method for rapidly estimating changes in turgor pressure by creating cavitation microbubbles by laser directly inside epidermal cells. In practice, a laser beam is focused through the microscope objective. The image of the rapid nucleation of the bubbles is recorded live by a high-speed camera. The size of the bubble, less than 4 microns, and its lifetime, less than 100 milliseconds, vary according to the pressure. Small bubbles that dissolve quickly are a sign of high pressure. This made it possible to carry out a large number of pressure measurements on a wide range of plant species.
Thanks to this new technique, the researchers were able to reveal a surprising difference between species: the stomata of non-vascular plants (bryophytes: mosses, liverworts, anthocerota) do not respond to light, unlike the stomata of vascular plants, which increase their turgor pressure in response to light. Bryophyte stomata open later and irreversibly, triggering a process of dehydration and spore dispersal. The results are published in the Proceedings of the National Academy of Science.
