In the world of plants, a molecular tug-of-war dictates when pores known as stomata open to allow the important processes of photosynthesis and transpiration—and when they close to prevent water loss. Now, new research from Carnegie's Wolf Frommer and colleagues shows that the stomata's "molecular switch" is a delicate balance of forces regulated by hydrogen sulfide gas.

"By understanding precisely how plants control the opening and closing of their stomata, we can potentially engineer more efficient water-use strategies to withstand increasingly erratic climatic conditions," Frommer explained.

The research is published in the Proceedings of the National Academy of Sciences. Stomata are minuscule gatekeeper pores found in leaves and stems that allow carbon dioxide to enter and water vapor to exit during photosynthesis and transpiration. Understanding the molecular mechanisms underlying their regulation offers insights into the ability of plants to tolerate environmental stresses, such as drought and high salinity, and could allow scientists to develop crops with improved water-use efficiency.

For decades, scientists have known that the plant hormone abscisic acid (ABA) triggers the closure of stomata in response to drought or other stresses. ABA was previously thought to act exclusively on a molecule known as the "slow anion channel" (SLAH3) at the stomata to limit water loss.

However, a 2018 study by Frommer's team turned the long-held understanding of ABA signaling upside down. They discovered that SLAH3 is not directly responsible for stomatal movements but rather regulates the production of hydrogen sulfide gas, which in turn triggers the opening of stomata.

Their latest study builds upon this finding, unveiling the complete picture of how hydrogen sulfide is involved in stomatal movements and how it interacts with ABA signaling. Using a combination of physiological, biochemical, and molecular techniques, the team found that ABA inhibits SLAH3 channel activity, which increases hydrogen sulfide production and promotes stomatal opening. On the other hand, in the absence of ABA or under conditions that deplete hydrogen sulfide levels, stomata close.

"Our study establishes hydrogen sulfide as a key molecule that mediates the intricate coordination of stomatal movements with other environmental cues and conditions, providing a molecular mechanism that plants use to integrate external stimuli with their internal physiology," Frommer concluded.

The findings may have implications for plant breeding and engineering strategies aimed at improving crop performance under various environmental conditions, including drought and high salinity.