Rubisco, Rubisco activase, and global climate change

Area of Science:

• Plant Physiology
• Climate Change Biology
• Biochemistry

Background:

• Global warming and increased atmospheric CO2 will elevate leaf temperatures, potentially exceeding optimal levels for photosynthesis.
• Current models debate whether electron transport or Rubisco activase capacity limits photosynthesis at high temperatures.
• Distinguishing between these limitations is challenging as they can be interdependent.

Purpose of the Study:

• To investigate methods for identifying photosynthetic limitations at elevated temperatures.
• To assess if the initial slope of the CO2 response of photosynthesis (A/Ci response) can screen for Rubisco activase limitations.
• To determine the primary limiting factors of photosynthesis in black spruce under high temperatures.

Main Methods:

• Utilized biochemical and gas exchange assessments.
• Measured the initial slope of the CO2 response of photosynthesis (A/Ci response).
• Modeled the A/Ci response using kinetic parameters of fully activated Rubisco.

Main Results:

• In sweet potato, spinach, and tobacco, high temperatures did not reveal Rubisco activase limitations.
• The initial slope of the A/Ci response in these species was accurately modeled by fully activated Rubisco kinetics.
• Black spruce showed a reduced initial slope above 30°C, unexplainable by fully activated Rubisco, indicating potential Rubisco activase limitation.

Conclusions:

• The initial slope of the A/Ci response is a potential screening tool for Rubisco activase limitations.
• Rubisco activase may be a critical factor limiting photosynthesis in black spruce at high temperatures.
• Understanding Rubisco activase function is crucial for predicting the boreal forest's response to climate change.