Photorespiration

Photorespiration (also known as the oxidative photosynthetic carbon cycle, or C2 photosynthesis) refers to a process in plant physiology where the enzyme RuBisCO oxygenates RuBP, causing some of the energy produced by photosynthesis to be wasted. The process is highly energy-intensive and can reduce the efficiency of photosynthesis, particularly under certain environmental conditions.

Process

Photorespiration begins in the chloroplasts, where RuBisCO acts on oxygen instead of carbon dioxide. This results in a two-carbon compound that is exported to the peroxisome, where it is converted to glycolate. The glycolate is then transported to the mitochondria for conversion into glycine.

In the mitochondria, two molecules of glycine are converted into one molecule of serine, releasing carbon dioxide and ammonia. The serine is then transported back to the peroxisome where it is converted into glycerate, which is then transported back to the chloroplasts to be converted back into RuBP, completing the cycle.

Environmental Factors

The rate of photorespiration is influenced by environmental conditions. High temperatures, high light intensities, and low carbon dioxide levels can all increase the rate of photorespiration. This is because these conditions favor the oxygenase activity of RuBisCO over its carboxylase activity.

Impact on Plant Growth

Photorespiration can have a significant impact on plant growth and productivity. It can reduce the efficiency of photosynthesis by up to 50%, which can limit plant growth and reduce crop yields. Some plants, such as C4 plants and CAM plants, have evolved mechanisms to minimize the impact of photorespiration.

See Also

• C3 carbon fixation
• C4 carbon fixation
• Crassulacean acid metabolism
• RuBisCO

Photorespiration Resources
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