Photorespiration


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Photorespiration

Light-dependent carbon dioxide release and oxygen uptake in photosynthetic organisms caused by the fixation of oxygen instead of carbon dioxide during photosynthesis. This oxygenation reaction forms phosphoglycolate, which represents carbon lost from the photosynthetic pathway. Phosphoglycolate also inhibits photosynthesis if it is allowed to accumulate in the plant. The reactions of photorespiration break down phosphoglycolate and recover 75% of the carbon to the photosynthetic reaction sequence. The remaining 25% of the carbon is released as carbon dioxide. Photorespiration reduces the rate of photosynthesis in plants in three ways: carbon dioxide is released; energy is diverted from photosynthetic reactions to photorespiratory reactions; and competition between oxygen and carbon dioxide reduces the efficiency of the important photosynthetic enzyme ribulose-bisphosphate (RuBP) carboxylase. There is no known function of the oxygenation reaction; most scientists believe it is an unavoidable side reaction of photosynthesis. See Photosynthesis

The rate of photosynthesis can be stimulated as much as 50% by reducing photorespiration. Since photosynthesis provides the material necessary for plant growth, photorespiration inhibits plant growth by reducing the net rate of carbon dioxide assimilation (photosynthesis). Plants grow faster and larger under nonphotorespiratory conditions, in either low oxygen or high carbon dioxide atmospheres. Most of the beneficial effects on plant growth achieved by increasing CO2 may result from the reduced rate of photorespiration. See Plant growth

There are some plants that avoid photorespiration under certain conditions by actively accumulating carbon dioxide inside the cells that have ribulose-bisphosphate carboxylase/oxygenase. Many cacti do this by taking up carbon dioxide at night and then releasing it during the day to allow normal photosynthesis. These plants are said to have crassulacean acid metabolism (CAM). Another group of plants, including corn (Zea mays), take up carbon dioxide by a special accumulating mechanism in one part of the leaf, then transport it to another part of the leaf for release and fixation by normal photosynthesis. The compound used to transport the carbon dioxide has four carbon atoms, and so these plants are called C4 plants. Plants that have no mechanism for accumulating carbon dioxide produce the three-carbon compound phosphoglycerate directly and are therefore called C3 plants. Most species of plants are C3 plants. See Plant respiration

Photorespiration

 

the process occurring in plant cells under the action of light by which oxygen is absorbed and carbon dioxide is given off.

The mechanism of photorespiration and the enzymes participating in the process have not yet been thoroughly studied. It is conjectured that in photorespiration the reduced substances formed during electron transfer in photosynthesis are oxidized in reactions of reciprocal conversions of glycolic and glyoxylic acids. In some plants photorespiration is intense, with as much as 50 percent of the reduced nicotinamide adenine dinucleotide phosphate (NADP-N) formed during photosynthesis being expended. In a number of tropical plants photorespiration is not observed. It is believed that selective suppression of photorespiration by means of specific inhibitors might increase the productivity of a number of agricultural plants.

REFERENCES

Lehninger, A. Biokhimiia, ch. 21. Moscow, 1974. (Translated from English.)

photorespiration

[¦fōd·ō‚res·pə′rā·shən]
(biochemistry)
Respiratory activity taking place in plants during the light period; CO2 is released and O2 is taken up, but no useful form of energy, such as adenosinetriphosphate, is derived.
References in periodicals archive ?
When a plant uses less energy on photorespiration, it ''is able to take that energy and put it into plant growth and plant productivity, rather than using it to metabolize this toxic compound.''
"We could feed up to 200 million additional people with the calories lost to photorespiration in the Midwestern U.S.
It is happened because methanol got oxidation in increasing the photosynthesis rate of potato and suppressed the photorespiration due to an increased C[O.sub.2], leaves intern, which enable ribulose diphosphate-carboxylase compared with ribulose diphosphate-oxidase [17,18,].
Wild, "Effect of phosphinothricin (glufosinate) on photosynthesis and photorespiration of C3 and C4 plants," Photosynthesis Research, vol.
Photosynthesis, photorespiration, and dark respiration in eight species of algae.
C4 plants possess biochemical and anatomical mechanisms to raise the intercellular carbon dioxide concentration at the site of fixation; this reduces (and sometimes eliminates) carbon losses by photorespiration. Both C3 and C4 plants were thought to close stomata at night.
A marked increase in P protein subunit of glycine associated with photorespiration was found in 150 mM As-stressed plants.
Hageman, "Varietal effects in soybean photosynthesis and photorespiration," Crop Science, vol.
subcordiformis had also observed that the reduction in MDA at high concentrations of C[O.sub.2] was due to reduced photorespiration that simultaneously reduced photoreduction of dioxygen.
Dove, "The effect of ocean acidification on symbiont photorespiration and productivity in Acropora formosa," Global Change Biology, vol.