Mechanical forces and cell shape guide how plant stomata form

Scientists have uncovered how the interplay between cell shape and mechanical stress influences the orientation of stomata (microscopic pores on the leaf surface) during early plant development.

Stomata, from the Greek word for mouth, are essential gateways that regulate the exchange of carbon dioxide and oxygen, as well as water loss.

The stomatal density and how efficiently stomata open and close in response to stress strongly influences how effectively plants capture carbon dioxide for photosynthesis and limit water loss during drought.

In the longer term, a better understanding of stomata could help researchers design crops with improved water-use efficiency and resilience to drought.

Stomata development

Each pore is formed by a pair of specialised guard cells that open and close in response to environmental cues, playing a central role in plant survival and productivity.

While researchers have long known of the key genetic regulators that control stomatal development, including transcription factors SPEECHLESS and MUTE (which act sequentially, to initiate and terminate the stomatal cell state) it remains unclear what determines the orientation of the stomata on the leaf.

Using the model plant, Arabidopsis thaliana, researchers from Dr Sarah Robinson’s research group at the Sainsbury Laboratory Cambridge University (SLCU) combined live imaging and computational modelling to investigate how stomata are orientated during early leaf development. The research was published in Cell Reports.

The team tracked more than 10,000 stomata from 72 embryonic leaves (cotyledons) over the first five days after seed germination.

“Our results show that stomatal divisions are strongly guided by the geometry of the cell,” said Dr Leo Serra, who is the first author of the study. “In most cases they align with the long axis of the cell, which is unusual when compared with many other plant cell types.”

However, this did not explain the organ scale alignment of stomata they observed. The team found that cell shape is only part of the story.

Mechanics comes into force

By modelling growth patterns and experimentally altering mechanical forces within the young plants, the researchers demonstrated that when tensile strength was generated as the leaf expanded, it influenced the orientation of guard cell divisions.

“When we altered the mechanical forces applied to the leaf we saw clear changes in stomatal division orientations,” said Dr Euan Smithers, who conducted the modelling. “This suggests that mechanical stress might override geometric cues.

“We found that stomatal divisions tend to align with the long axis of the cell but can be influenced by mechanical stress,” said Dr Robinson. 

“While stomatal divisions show a strong alignment with the cell’s geometry, mechanical perturbation confirmed the influence of tensile stress on stomata division orientation.” 

The researchers also discovered striking differences between the adaxial (upper) and abaxial (lower) sides of the leaf. 

These two sides grow at different rates (the adaxial side growing faster than the abaxial side), creating distinct patterns and levels of tensile forces across the leaf surface.

As a result, stomatal orientation varies over time and between surfaces.

In the abaxial side (where stomata are more abundant) divisions closely align with the leaf axis, but become more variable as development progresses.

In contrast, on the adaxial side the stomatal orientation becomes disorganised much earlier. 

What causes the differences in alignment between adaxial and abaxial sides?

Dr Robinson says these differences most likely come from differential growth between the two sides of the leaf.

“Faster growth on the adaxial side leads to greater tensile stress relaxation, while slower growth on the abaxial side maintains more consistent tensile stress patterns, contributing to more coordinated stomatal alignment,” she said. 

Visualising stress patterns using mutants with weakened cells adhesion

To disentangle the relative contributions of geometry, growth, and mechanical stress, the team used time-lapse imaging and advanced image analysis to track cell lineages and quantify division orientations. They used mutant plants with weakened cell adhesion, allowing stress patterns to become visible as cracks on the leaf surface. 

Applying mechanical stress by leaf bending

It can be challenging to apply mechanical stress to very small tissues.

"We found a way to bend the leaves to cause a change in the stress patterns at the surface of the leaf. We found that this was sufficient to alter the orientation of the stomata," said Dr Serra. 

Dual influences on stomata orientation

Their analyses revealed that, although stomatal divisions are most often aligned with the long axis of the cell, they can also align with predicted patterns of organ-scale tensile stress, particularly in cells with more isotropic shapes.

This finding is consistent with observations in other plant tissues, where cell divisions often follow the direction of maximal mechanical stress.

“Geometry appears to be the dominant factor guiding stomatal orientation, but mechanical stress can take over in certain contexts,” said Dr Robinson. “This dual control may help coordinate cell behaviour across the tissue.”

Although the study, which was published in Cell Reports, did not directly test how stomatal orientation affects function, the researchers suggest aligning stomata with mechanical stress patterns may optimise how efficiently pores open and close.

“Since stomata themselves generate mechanical forces on neighbouring cells, sensitivity to stress may also help position new stomata in ways that improve overall performance,” Dr Robinson said.

“Our work highlights how mechanical context shapes biological outcomes. There is still a lot to learn about how plants generate patterns that can span across whole organs. 

Reference

Leo Serra, Euan T. Smithers, Lucy Bentall, Martin O. Lenz, Sarah Robinson (2026) Geometry and mechanical stress influences stomata division. Cell Reports. DOI: 10.1016/j.celrep.2026.117366