Photorespiration

Definition

Photorespiration is a process that occurs in plants where the enzyme RuBisCO reacts with oxygen instead of carbon dioxide, leading to the production of a two-carbon compound and ultimately resulting in the loss of fixed carbon and energy. This process can be seen as a wasteful side reaction that interferes with the efficiency of the Calvin cycle, particularly under conditions of high light intensity and low carbon dioxide availability. Understanding photorespiration is essential for grasping alternative carbon fixation pathways and the regulation of photosynthesis.

5 Must Know Facts For Your Next Test

1. Photorespiration occurs when RuBisCO binds with oxygen instead of carbon dioxide, which can lead to a significant decrease in photosynthetic efficiency.
2. The process consumes energy and releases fixed carbon dioxide back into the atmosphere, which can reduce overall plant productivity.
3. Photorespiration is more common in C3 plants compared to C4 and CAM plants, which have evolved mechanisms to minimize this wasteful process.
4. Environmental conditions such as high temperatures and low carbon dioxide concentrations can exacerbate photorespiration, especially during intense light periods.
5. Strategies to mitigate photorespiration include genetic engineering to enhance the efficiency of RuBisCO or developing plants that utilize C4 or CAM pathways.

Review Questions

• How does photorespiration affect the efficiency of the Calvin cycle in plants?
  • Photorespiration negatively impacts the efficiency of the Calvin cycle by causing RuBisCO to react with oxygen instead of carbon dioxide. This leads to the formation of a two-carbon compound that is subsequently broken down, resulting in the loss of previously fixed carbon and energy. This side reaction ultimately reduces the amount of glucose produced during photosynthesis and can significantly hinder plant growth, especially in environments where conditions favor photorespiration.
• Discuss how C4 and CAM pathways help mitigate the effects of photorespiration compared to C3 plants.
  • C4 and CAM pathways help reduce photorespiration by separating the initial carbon fixation from the Calvin cycle's main processes. C4 plants utilize a different enzyme to initially capture carbon dioxide in mesophyll cells, forming a four-carbon compound that is then transported to bundle-sheath cells where the Calvin cycle occurs. CAM plants, on the other hand, open their stomata at night to fix carbon dioxide when temperatures are cooler and transpiration rates are lower. Both strategies effectively minimize RuBisCO's exposure to oxygen, thereby reducing the likelihood of photorespiration and increasing overall photosynthetic efficiency.
• Evaluate the significance of understanding photorespiration in terms of enhancing agricultural productivity in response to climate change.
  • Understanding photorespiration is crucial for improving agricultural productivity as climate change leads to more frequent high temperatures and altered atmospheric CO2 levels. By recognizing how this process limits photosynthesis in C3 crops, researchers can develop strategies to mitigate its effects through breeding programs or genetic engineering aimed at enhancing RuBisCO efficiency or introducing C4 traits into C3 species. Such advancements could enable crops to maintain higher productivity under stress conditions, ensuring food security while addressing the challenges posed by a changing climate.

Related terms

RuBisCO: Ribulose bisphosphate carboxylase/oxygenase, an enzyme that catalyzes the first major step of carbon fixation in the Calvin cycle.

C3 Plants: Plants that utilize the Calvin cycle for carbon fixation, with RuBisCO as the primary enzyme, often leading to photorespiration under certain conditions.

Oxygenase Activity: The ability of RuBisCO to catalyze reactions with oxygen, leading to photorespiration rather than carbon fixation.