Plants have a secret 'breathing' strategy in response to heat

As global temperatures rise, scientists are increasingly studying how plants adapt to these changing conditions, paying particular attention to tiny structures known as stomata.

These micro-pores, located on leaf surfaces, play a vital role in regulating water loss, facilitating gas exchange, and managing carbon dioxide intake for photosynthesis and growth.

Stomata serve as the plant’s natural cooling system. During heatwaves, these pores respond by widening, allowing the plant to release water vapor and cool down, ensuring it survives the elevated temperatures and continues functioning effectively.

Cracking the code of plant heat response

However, for more than a century, researchers have been stumped by the intricate processes behind this stomatal “breathing” and have struggled to understand the genetic and molecular mechanisms behind transpiration processes in response to heat.

In a new study from the University of California San Diego School of Biological Sciences, led by PhD student Nattiwong Pankasem and Professor Julian Schroeder, scientists have uncovered new details about these plant mechanisms.

The findings, published in the journal New Phytologist, highlight two genetic pathways plants use to handle increasing temperatures.

“With increasing global temperatures, there’s obviously a threat to agriculture with the impact of heat waves,” said Schroeder.

“This research describes the discovery that rising temperatures cause stomatal opening by one genetic pathway, but if the heat steps up even further, then there’s another mechanism that kicks in to increase stomatal opening.”

Two pathways to stomatal opening

The researchers discovered that as temperatures rise, one genetic pathway primarily controls stomatal opening to regulate water loss and gas exchange.

But as the heat intensifies beyond a certain threshold, a second, more robust pathway steps in to further increase stomatal opening, enhancing the plant’s ability to cool itself under extreme conditions.

This discovery provides insights into how plants manage their internal temperatures, enabling them to survive even in the face of escalating global warming.

Complexity of plant heat responses

Deciphering these mechanisms has long been a challenge due to the complexity of separating temperature and humidity responses.

Pankasem solved this problem by developing a novel method for clamping the vapor pressure difference (VPD) of leaves to fixed values as temperatures rise.

This allowed the research team to tease out the genetic mechanisms of stomatal temperature responses, including the role of blue-light sensors, drought hormones, carbon dioxide sensors, and temperature-sensitive proteins.

Stomatal responses in action

Pankasem and his colleagues examined the genetic responses in two plant species: Arabidopsis thaliana, a weed species, and Brachypodium distachyon, a flowering plant related to key grain crops such as wheat, maize, and rice.

The team discovered that carbon dioxide sensors play a pivotal role in the stomatal response to heat.

As leaves warm, these sensors trigger an increase in photosynthesis, reducing carbon dioxide levels and causing stomatal pores to open. This allows the plant to take in more carbon dioxide and benefit from enhanced photosynthesis.

A second heat response in plants

Under extreme heat, however, photosynthesis slows and the stomatal heat response bypasses the carbon dioxide sensor system. This triggers the secondary heat response pathway to open the stomata and cool the plant.

“The impact of the second mechanism, in which plants open their stomata without gaining benefits from photosynthesis would result in a reduction in water use efficiency of crop plants,” said Pankasem.

“Based on our study, plants are likely to demand more water per unit of CO2 taken in, which could directly affect irrigation planning and hydrological cycles in response to global warming.”

Implications for agriculture

“This work shows the importance of curiosity-driven, fundamental research in helping to address societal challenges, build resiliency in key areas like agriculture, and, potentially, advance the bioeconomy,” noted Richard Cyr, a program director at the U.S. National Science Foundation.

With these findings in hand, Pankasem and Schroeder are now turning their focus toward understanding the molecular and genetic mechanisms behind the secondary heat response system. This could lead to new strategies for reducing water consumption in agriculture amidst rising global temperatures.

The study is published in the journal New Phytologist.

—–

Like what you read? Subscribe to our newsletter for engaging articles, exclusive content, and the latest updates. 

Check us out on EarthSnap, a free app brought to you by Eric Ralls and Earth.com.

—–