Mythili Subbanna is a rising junior from Scarsdale, NY. She studies Mathematics – while also taking biology, chemistry, and physics coursework – at Amherst College in Amherst, MA. This summer, in the Anderson/Shenoy Lab, she will measure plant cell volumes and model water/ion flow in and out of cells to understand how these processes are influenced by cell wall mechanics, and how they affect cell pressurization and stomatal dynamics. In the future, she hopes to do applied mathematical modeling research, as well as pursue a PhD in biomedical engineering or materials science engineering.
Measuring and Modeling How Turgor Pressure-Driven Mechanical Forces Between Guard and Pavement Cells Underlie Stomatal Opening and Closing
Mythili Subbanna, Emily Walter
Stomata are pores in the plant surface that facilitate photosynthesis and transpiration. In Arabidopsis thaliana, stomatal complexes comprise two kidney-shaped guard cells, and are flanked by neighboring pavement cells. The pathways by which cytosolic pressure changes, brought about by ion flux, drive cell inflation and deflation during stomatal opening and closing have been widely studied. However, the dynamic mechanical interactions between guard and pavement cells remain poorly understood. Here, we sought to identify how changes in guard cell shape might influence surrounding pavement cells. We hypothesized that during stomatal opening, guard cell area would increase, imposing stress on neighboring pavement cells, thus decreasing neighboring pavement cell size, with opposite trends for both during stomatal closure.
We incubated seedlings in either fusicoccin plus light or abscisic acid (ABA) plus darkness to induce stomatal opening or closure, respectively, and measured changes in cell area over 2.5 hours. Fusicoccin-treated guard and non-neighboring pavement cells expanded relative to neighboring pavement cells. Conversely, ABA-treated guard cells shrank while ABA-treated neighboring pavement cells expanded. We developed a theoretical model to simulate stimulus-dependent changes in ion flux, osmotic potential, and guard and pavement cell size. Loading induced by guard cell expansion was predicted to cause pavement cell shrinking via an increase in hydrostatic pressure that drives fluid and ionic efflux. Realistic cell models were constructed using finite element software. Simulations were consistent with our hypothesis that stomatal opening imposes stress on neighboring pavement cells. These results provide new insights into plant mechanotransduction and turgor pressure regulation.