PHOTORESPIRATION
- PHOTORESPIRATION first demonstrated by Decker in 1955 and 1959.
‘The Photorespiration defined as “the Respiration that occurs in green cells in the presence of light resulting into excess evolution of CO2”
OR
“The release of CO2 in Respiration in presence of light.”
- Always required light to perform.
- The photorespiration rate of reaction takes place at 25℃-35℃.
- Depending on oxygen concentration to takes place of this process.
- Photorespiration is diffrent from Dark Respiration.
- Photorespiration is also known as the C2 cycle.
- Photorespiration takes place in different green cells of plants
as: Pisum
Oryza
Glycine
Capsicum
Nicotiana
Pisum
Petunia
Antirrhinum
Chlorella
Nitella
Helianthus
Gossiping
Phaseolus - It also is known as the oxidative photosynthetic carbon cycle, or C2 photosynthesis.
SITE OF PHOTORESPIRATION
The three cell-organelles: Chloroplasts, Peroxisomes, and the Mitochondria together actively participate in Photorespiration to form the Site of Photorespiration.
SIGNIFICANCE OF PHOTORESPIRATION
- It helps to fast the photosynthesis process by increasing the concentration of CO2 in intercellular spaces of leaf tissue.
- Photorespiration process is important so we can classify the plants in two groups as:
1. Plants without Photorespiration.
2. Plants with Photorespiration.
Pisum Oryza Glycine Capsicum Nicotiana Pisum Petunia Antirrhinum Chlorella Nitella Helianthus Gossiping Phaseolus
| Characteristics | With Photorespiration | Without Photorespiration |
|---|---|---|
| Enhancement of CO2 assimilation in light and low oxygen. | Yes | No |
| CO2 compensation point in light. | 15 to 150ppm | 0 ppm |
| CO2 assimilation rate in intense light. | 15 to 35 mg CO2/dm2/h | 50 to 70 mg CO2/dm2/h |
| CO2 evolution in light. | High rate | Apparently nil |
| Internal structure of leaf. | Diffuse mesophyll | Mesophyll compact about vascular bundles. |
| Carbon pathway | Calvin cycle | Calvin cycle and HATCH and SLACK pathway both |
| Carbonic anhydrase activity. | High | Low |
| Translocation rate from leaf. | Low | High |
| Temperature optimum for photosynthesis and growth. | Low to high | High |
- The photorespiration process can take place in a very low concentration of oxygen too.
- The rate of Photorespiration decreased with the increase of CO2 in the atmosphere.
Difference Between Photorespiration and Dark Respiration
| PHOTORESPIRATION | DARK RESPIRATION |
|---|---|
| It takes place only in presence of light. | It occurs in light and Dark both conditions. |
| It occurs only in green cells. | It occurs in all living cells. |
| The respiratory substrate in Photorespiration is 2-carbon glycolic acid. | The respiratory substrate in dark Respiration may be carbohydrates, fats or protiens. |
| Respiratory substrate is immediately formed. | Respiratory substrate may be previously stored or immediately formed. |
| It occurs among chloroplasts, cytoplasm, peroxisomes and mitochondria. | It occurs in cytoplasm and mitochondria. |
| During Photorespiration, hydrogen peroxide (H2O2) is formed. | H2O2 is not formed. |
| ATP molecules are not synthesized. | ATP molecules are synthesized. |
| NADH is oxidised to NAD+. | NAD+is reduced to NADH+ H+. |
| The process of transamination occurs during Photorespiration. | This process does not occurs during dark Respiration. |
| It depends upon O2 concentration and is directly proportional to it. | O2 concentration has no affect on this process. |
| It's maximum rate is in between 25℃-35℃. | It's maximum rate is in between 35℃-40℃. |