During photorespiration in plants, carbon dioxide is produced when glycine is converted to serine in mitochondria.

- Introduction: Photorespiration is a metabolic process that occurs in plants when there is a deficiency of carbon dioxide (CO2) and an excess of oxygen (O2). It is an inefficient process that competes with the more favorable process of photosynthesis. One of the key reactions in photorespiration is the conversion of glycine to serine.

- Glycine to Serine Conversion: Glycine, an amino acid, is converted to serine through a series of enzymatic reactions. The first step involves the conversion of glycine to glyoxylate, catalyzed by the enzyme glycine decarboxylase complex (GDC). The glyoxylate then reacts with a molecule of glutamate to form glycine and α-ketoglutarate. The second step involves the conversion of glycine to serine, catalyzed by the enzyme serine hydroxymethyltransferase. This reaction requires tetrahydrofolate (THF) as a coenzyme.

- Location of the Reaction: The conversion of glycine to serine occurs in the mitochondria of plant cells. Mitochondria are the powerhouses of the cell and are responsible for various metabolic processes, including the breakdown of organic molecules to produce energy in the form of ATP. In the case of photorespiration, mitochondria play a crucial role in the metabolism of glycine.

- Carbon Dioxide Production: During the conversion of glycine to serine, carbon dioxide is released as a byproduct. This occurs in the mitochondria, where the glycine decarboxylase complex catalyzes the decarboxylation of glycine, resulting in the release of CO2. The released carbon dioxide can then diffuse out of the mitochondria and be released into the surrounding environment.

- Significance: The production of carbon dioxide during photorespiration is one of the reasons why it is considered an inefficient process. The release of CO2 reduces the net carbon gain of the plant, as it counteracts the carbon fixation that occurs during photosynthesis. This can have negative effects on plant growth and productivity, especially under conditions of high temperature and low carbon dioxide availability.

In conclusion, during photorespiration in plants, carbon dioxide is produced when glycine is converted to serine in the mitochondria. This process occurs as a part of the metabolic pathway in response to a deficiency of carbon dioxide and an excess of oxygen, and it can have significant implications for plant growth and productivity.