How plants decide where to put their breathing pores

Plants turn air into leaves, roots, and fruit, yet every molecule of the carbon they store has to squeeze through microscopic pores first. These pores, called stomata, dot the surface of nearly every leaf and set the pace for both growth and water loss.

The latest study from Stanford University shows that each new stoma is the product of a lively conversation among neighboring cells and a hard look in the mirror.

Dominique Bergmann and her team traced those talks in Arabidopsis (Arabidopsis thaliana), the small mustard plant whose genome was first decoded in 2000.

How plants form and adjust pores

Stomata behave like adjustable valves, opening when light and water are plentiful and closing when drought or darkness loom. Their numbers are not fixed; plants can make more or fewer during development, tweaking their gas exchange to match the environment.

For that plasticity to work, precursor cells must decide whether to divide again or settle down as part of the pavement around a stoma.

The new research focuses on these larger daughters, called stomatal lineage ground cells, which had been thought to be passive passengers in leaf development.

The Stanford team captured day‑long movies of living leaves and tracked every fate choice. They discovered that the future of each cell depends on its own size and on the crowd of neighbors encircling it.

Plants use nearby cells to control pores

Signals drift through the leaf in the form of tiny peptides such as epidermal patterning factor 1 (EPF1) and its sibling EPF2, which tell nearby cells to slow down or stop forming new stomata.

Because these messages travel only a short distance, the number of stomatal precursors touching a cell sets the strength of the “slow down” order.

Cells bordered by two or more precursors received a louder signal and dismantled an internal protein called SPEECHLESS before it could trigger another split. Those with just one signaling neighbor heard only a whisper and often went on to divide again.

The researchers measured how fast SPEECHLESS disappeared and found that the rate jumped with every extra neighbor. By evening, many well‑connected cells had emptied their nuclei of the division‑promoting factor and settled into a quiet life as pavement.

The role of cell size

Size turned out to be the second half of the script. When two sister cells emerged from a split, one was noticeably larger and carried a larger nucleus.

Bigger nuclei diluted the amount of SPEECHLESS even before degradation kicked in, pushing the concentration below the threshold needed to spark another round of division. Smaller sisters packed the protein more tightly and were free to keep the lineage going.

To confirm the link, the team boosted SPEECHLESS levels across the board. Large cells that normally would have retired instead re‑entered the cell cycle, proving that concentration, not mere presence, calls the shots.

Plants use internal guides to shape pores

“Compasses have dual roles,” said Bergmann. The study builds on earlier work showing that internal “compasses” guide each split so that one daughter remains small and stem‑like while the other grows large. 

Bergmann explained that the same molecular north arrow orients the division plane and then reorganizes the contents of the newborn cells to cement their different futures.

Computational models confirmed that size, neighbor count, and SPEECHLESS levels together predict a cell’s fate better than any factor alone.

Warm nights add another twist: higher temperatures activate a photoreceptor called PIF4 that limits SPEECHLESS production, cutting back the formation of new stomata.

The Stanford data suggest that heat might tilt the balance further by shrinking protein levels just enough to keep big cells out of the cell cycle.

Improving crops and farming

Why should anyone without a microscope care how many times a leaf cell divides? Because every stoma trades water for carbon, the final stomatal count shapes a crop’s thirst and yield.

Breeders are already lowering stomatal density in wheat, barley, and rice to save water without hurting photosynthesis. Knowing that cell size and neighbor signals tune those numbers could make such tweaks more precise and less likely to backfire.

The work also hints at strategies for future‑proofing plants against heat waves. If larger precursor cells naturally avoid dividing under high temperature, selecting varieties with slightly bigger epidermal cells could be a subtle way to reduce water loss.

There is an evolutionary angle as well. Fossil leaves show that ancient plants reduced their stomatal density when atmospheric CO₂ climbed, mirroring the choices Bergmann’s cells make on a microscopic scale.

Understanding the cell‑level logic may help scientists read the rock record more accurately and model how modern forests will respond to rising greenhouse gases. It could even inform designs for synthetic leaves or bio‑inspired materials that need self‑regulating pores.

Research on plants and their pores

The Bergmann lab now wants to trace the still‑mysterious signals that link cell size to peptide output. They suspect a size‑sensing pathway unrelated to SPEECHLESS that may give big cells an extra nudge toward differentiation.

If that circuit can be mapped, it might be possible to rewire it, allowing crops to adjust their stomata on demand without penalties in growth. Such control would be a powerful tool in regions where water scarcity and heat routinely threaten harvests.

The study is published in the journal Nature Communications.

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