As temperatures rise, researchers identify mechanisms behind plants’ response to warming

Microscopic pores on the surface of leaves, called stomata, help plants “breathe” by controlling the amount of water they lose through evaporation. These stomatal pores also allow and control the supply of carbon dioxide for photosynthesis and growth.

As early as the 19th century, scientists knew that plants expanded their stomatal pores to transpire, or “sweat,” by sending water vapor through the stomata to cool themselves. Today, with increasing global temperatures and heat waves, stomatal pore enlargement is considered a key mechanism to minimize heat damage to plants.

But for more than a century, plant biologists have failed to fully understand the genetic and molecular mechanisms behind increased stomatal “breathing” and transpiration processes in response to high temperatures.

University of California San Diego School of Biological Sciences, Ph.D. student Nattiwong Pankasem and professor Julian Schroeder have drawn up a detailed picture of these mechanisms. Their conclusions, published in the journal New plant scientistidentify two pathways that plants use to cope with rising temperatures.

“With global temperatures increasing, agriculture is obviously threatened by the impact of heat waves,” Schroeder said. “This research describes the finding that rising temperatures cause stomata to open through a genetic pathway (mechanism), but if the heat intensifies even more, then there is another mechanism that comes into play to increase the opening of the stomata.”

For decades, scientists have struggled to find a clear method to decipher the mechanisms underlying temperature-induced increases in stomatal openings, due to the complex measurement processes required. The difficulty lies in the complex mechanics involved in adjusting air humidity (also known as vapor pressure difference, or VPD) to constant values ​​as temperature increases, and in the difficulty of distinguishing temperature and humidity responses.

Pankasem helped solve this problem by developing a new approach to maintain leaf VPD at fixed values ​​under increasing temperatures. He then uncovered the genetic mechanisms for a range of responses to stomatal temperature, including factors such as blue light sensors, drought hormones, carbon dioxide sensors and temperature-sensitive proteins.

A new generation gas exchange analyzer that allows better control of the VPD (by setting the VPD to fixed values) was important for this research. Researchers can now conduct experiments to elucidate the effects of temperature on stomata opening without needing to remove leaves from entire living plants.

The results revealed that the response to stomatal warming is driven by a mechanism present in all plant lineages. In this study, Pankasem investigated the genetic mechanisms of two plant species, Arabidopsis thaliana, a well-studied weed species, and Brachypodium distachyon, a flowering plant related to major cereal crops such as wheat, corn and rice, representing a timely model. for these crops.

The researchers found that carbon dioxide sensors play a central role in the warming and cooling responses of stomata. Carbon dioxide sensors detect when leaves are experiencing rapid warming. This triggers an increase in photosynthesis in the warming leaves, leading to a reduction in carbon dioxide. This then triggers the stomatal pores to open, allowing plants to benefit from the increased carbon dioxide supply.

Interestingly, the study also discovered a second pathway of response to heat. Under extreme heat, plant photosynthesis is stressed and diminished and the stomatal thermal response has been found to bypass the carbon dioxide sensor system and disconnect from normal photosynthesis-induced responses. Instead, stomata use a second pathway of response to heat, much like entering a back door into a house, to “sweat” as a cooling mechanism.

“The impact of the second mechanism, in which plants open their stomata without receiving the benefits of photosynthesis, would result in a reduction in the water use efficiency of crop plants,” Pankasem said. “According to our study, plants are likely to require more water per unit of CO₂ This may have direct implications for irrigation planning for agricultural production and the large-scale effects of increased plant transpiration in ecosystems on the hydrological cycle in response to global warming.

“This work shows the importance of curiosity-driven fundamental research to help address societal challenges, build resilience in key areas like agriculture, and potentially advance the bioeconomy,” said Richard Cyr , program director at the United States National Science Foundation. Department of Biological Sciences. “A better understanding of the molecular complexities that control the basis of stomatal function at higher temperatures could lead to strategies to limit the amount of water needed for agriculture in the face of global rising temperatures.”

With the new details in hand, Pankasem and Schroeder are now working to understand the molecular and genetic mechanisms behind the secondary thermal response system.

Co-authors of the study are: Nattiwong Pankasem, Po-Kai Hsu, Bryn Lopez, Peter Franks and Julian Schroeder.