C4 Pathway
The plants exhibiting the C4 pathway are called C4 plants and comprise 3% of flowering plants, which include maize, sorghum, sugarcane, and some other dicot plants. This pathway is also known as Hatch and Slack cycle because four carbon molecules (oxaloacetate) form as the first product of carbon fixation in plants. The C4 carbon fixation is evolved in such a way that it adapts to high light intensities, high temperatures, and dryness.
Photorespiration is not energy demanding, but leads to a net loss of CO2. Plants have developed different ways to cope with this problem of photorespiration. C4 photosynthesis is one of the successful ways evolved by plants to reduce photorespiration. C4 plants use PEP carboxylase to capture CO2 in the mesophyll cells. Instead of using CO2 in mesophyll cells, PEP carboxylase utilizes bicarbonate.
In Mesophyll Cell
- The CO2 entering the mesophyll cells from the atmosphere will be converted to bicarbonate by hydrating CO2 using carbonic anhydrase. This bicarbonate will bind with Phosphoenol Pyruvate (PEP) in presence of PEP carboxylase to form oxaloacetate.
- Oxaloacetate is the first stable compound having four carbons, so the pathway is C4 pathway. Then OAA is reduced to malate or aspartate which are four carbon compounds.
In Bundle Sheath Cell
- The malate/aspartate enters bundle sheath cells and releases CO2 inside bundle sheath through decarboxylation.
- The released CO2 is immediately fixed by RuBisCO which will be followed by a normal Calvin cycle.
- The remaining 3 carbon compounds Pyruvate formed after decarboxylation of malate will return to the mesophyll cell for next C4 cycle using energy in the form of ATP.
- Photorespiration is a major problem for plants in hot climates as it consumes O2 and releases CO2. During hot conditions, the plants close the stomata to conserve water but this leads to a drop in the CO2 concentration within the leaf, favoring photorespiration.
C3 and C4 Pathways
C3 and C4 are photosynthetic pathways present in terrestrial plants. C3 plants use the C3 pathway or Calvin cycle, and C4 plants use the C4 pathway, or Hatch-Slack pathway, for the dark reaction of photosynthesis. Photosynthesis is the process in which different bacteria like cyanobacteria and eukaryotes like green plants, and algae can convert solar energy to chemical energy. In this process, solar energy is absorbed and used to synthesize carbohydrates from carbon dioxide and water.
Table of Content
- What are C3 and C4 Pathways?
- C3 Pathway
- C4 Pathway
- Difference Between C3 and C4 Pathway
- FAQs on C3 And C4 Pathways
Contact Us