As Temperatures Rise, Researchers Reveal How Plants Respond

Tiny openings on the surface of leaves, known as stomata, allow plants to “breathe” by regulating water loss through evaporation. These pores also manage the intake of carbon dioxide necessary for photosynthesis and growth.

Since the 19th century, scientists have known that plants widen their stomatal pores to release water vapor, or “sweat,” through transpiration, helping them cool down. As global temperatures and heat waves increase, this process is seen as a crucial defense against heat damage.

However, for over a century, plant biologists have not fully understood the genetic and molecular mechanisms that drive this increased stomatal activity and transpiration in response to higher temperatures.

UC San Diego Researchers Uncover Two Key Pathways in Plant Response to Rising Temperatures

Now, UC San Diego Ph.D. student Nattiwong Pankasem and Professor Julian Schroeder have mapped out these mechanisms. Their research, published in New Phytologist, identifies two pathways plants use to cope with rising temperatures.

“With rising global temperatures, agriculture faces a clear threat from heat waves,” said Schroeder. “This research uncovers that rising temperatures trigger stomatal opening through one genetic pathway. However, when the heat intensifies, a second mechanism activates to further increase stomatal opening.”

For years, scientists struggled to identify the mechanisms behind temperature-driven stomatal openings due to the complexity of the measurements involved. The challenge lay in maintaining constant air humidity, or vapor pressure difference (VPD), as temperatures rose, making it difficult to separate temperature and humidity responses.

Innovative Technique Uncovers Genetic Mechanisms Behind Stomatal Responses to Heat

Pankasem addressed this issue by developing a new technique to maintain fixed VPD levels in leaves as temperatures increased. This allowed him to unravel the genetic mechanisms involved in various stomatal responses, including those influenced by blue-light sensors, drought hormones, carbon dioxide sensors, and temperature-sensitive proteins.

A key factor in this research was the use of a next-generation gas exchange analyzer, which offered better control over VPD. This technology enabled researchers to study temperature effects on stomatal openings without detaching leaves from living plants.

The findings revealed that the stomatal response to warming is controlled by a mechanism found across various plant lineages. Pankasem examined the genetic mechanisms in two plant species: Arabidopsis thaliana, a widely studied weed, and Brachypodium distachyon, a flowering plant related to major crops like wheat, maize, and rice, offering valuable insights for these agricultural species.

Carbon Dioxide Sensors Play a Central Role in Stomatal Responses to Temperature

The researchers identified carbon dioxide sensors as key to the stomatal responses to warming and cooling. These sensors detect rapid warming in leaves, which boosts photosynthesis and reduces carbon dioxide levels, prompting the stomata to open and increase carbon dioxide intake.

Interestingly, they also discovered a second heat response pathway. Under extreme heat, photosynthesis becomes stressed and declines, causing the stomatal response to bypass the carbon dioxide sensor system and disconnect from typical photosynthesis-driven processes. Instead, the stomata activate an alternative pathway, functioning like a “backdoor” cooling mechanism to release water vapor.

Second Heat Response Mechanism Reduces Water Use Efficiency in Crops

“The second mechanism, where stomata open without benefiting from photosynthesis, decreases water use efficiency in crops,” explained Pankasem. “Our study suggests plants may require more water for each unit of CO2 absorbed, which has implications for irrigation planning and the impact of increased transpiration on the water cycle under global warming.”

“This research underscores the value of fundamental, curiosity-driven science in addressing societal challenges, enhancing agricultural resilience, and advancing the bioeconomy,” said Richard Cyr, a program director at the U.S. National Science Foundation. “Understanding the molecular mechanisms controlling stomatal function at higher temperatures could help develop strategies to reduce water use in agriculture as global temperatures rise.”

Pankasem and Schroeder are now exploring the molecular and genetic mechanisms behind this secondary heat response pathway.

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

Read the original article on: Phys Org

Read more: Elevated CO2 Levels Cause Mineral Deficiency in Plants Resulting in Less Nutritious Crops