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The upcoming discussion will update you about the difference among C3, C4 and CAM Cycle.
Difference # C3-Plant (Cycle):
1. Site of the cycle i.e. leaf structure (Morphology)- Mesophyll.
2. 1st stable compound- PGA 3-carbon compound.
3. CO2-fixing enzyme- RuBP caroboxylase.
4. CO2-acceptor- RuBP.
5. Dark reaction through- Calvin cycle.
6. Chlorophylla: chb ratio- 3:1.
7. Isotopic discrimination 13c (1.1% in atm.)- -20 to -40%.
8. CO2-concentration (compensation point)- 30-70μ/lit. air to 50 ppm CO2.
9. Internal concentration of CO2 in illuminated leaves- High 200 ppm.
10. Saturation point for CO2 fixation- 500 ppm.
11. Light saturation point as % of full sunlight- Low (10-15)
12. Habitat- Mesophytes.
13. Example- Wheat.
14. Photosynthetic rate (Under optimal conditions (mgCO2/dm2/hour)- Medium (15-35).
15. Biomass production- Medium.
16. Pigment system (PS) present in chloroplast- Both PSI & PSII are present in all chloroplast.
17. Presence of calvin cycle enzymes- Mesophyll’s chloroplast.
18. Presence of Photorespiration- High.
19. Sensitivity to oxygen- High.
20. Water use Efficiency (No. of g. of H2O to produce 1 g. plant matter)- Low (380-900).
21. Optimum temperature- 10-25°C.
22. Response to CO2 enrichment- High
23. Net rate of CO2 fixation- 15-35 mg. of CO2 per dm2 of leaf area per hour.
Difference # C4-Plant (Cycle):
1. Site of the cycle i.e. leaf structure (Morphology)- Mesophyll + bundle sheath i.e. Kranz.
2. 1st stable compound- Oxaloacetic acid (or malic acid) C4-compound.
3. CO2-fixing enzyme- PEP carboxylase and RuBP-Co (i.e. RuBP Carboxylase).
4. CO2-acceptor- P E P.
5. Dark reaction through- (a) Hatch & Slack cycle and (b) Calvin Cycle.
6. Chlorophylla: chb ratio- 4:1.
7. Isotopic discrimination 13c (1.1% in atm.)- -10 to -20%.
8. CO2-concentration (compensation point)- < 10μ/lit. air to 1-5 ppm CO2.
9. Internal concentration of CO2 in illuminated leaves- Low 100 ppm.
10. Saturation point for CO2 fixation- Lower conc.
11. Light saturation point as % of full sunlight- High (100)
12. Habitat- Arid.
13. Example- Sugarcane.
14. Photosynthetic rate (Under optimal conditions (mgCO2/dm2/hour)- High (40-80).
15. Biomass production- High.
16. Pigment system (PS) present in chloroplast- In chloroplast of B.S. cells PSII is absent and hence dependent on mesophyll chloroplast for the supply of NADPH2.
17. Presence of calvin cycle enzymes- Absent in mesophyll’s chloroplast.
18. Presence of Photorespiration- Low.
19. Sensitivity to oxygen- Low or negligible.
20. Water use Efficiency (No. of g. of H2O to produce 1 g. plant matter)- High (250-350).
21. Optimum temperature- 30-45°C.
22. Response to CO2 enrichment- Negligible
23. Net rate of CO2 fixation- 40-80mg of CO2 per dm2 of leaf area per hour.
Difference # CAM Plant (Cycle):
1. Site of the cycle i.e. leaf structure (Morphology) – Mesophyll + vacuole.
2. 1st stable compound- C3 & C4 compound in day C4 in night.
3. CO2-fixing enzyme- RuBPCo and PEPCo.
4. CO2-acceptor- P E P.
5. Chlorophylla: chb ratio – ≥ 3:1.
6. Isotopic discrimination 13c (1.1% in atm.)- -11%.
7. CO2-concentration (compensation point)- 0.2μ/lit. air to <5μ/lit. air.
8. Internal concentration of CO2 in illuminated leaves- Medium.
9. Saturation point for CO2 fixation- Medium.
10. Light saturation point as % of full sunlight- Medium
11. Habitat- Xeric.
12. Example- Cactus.
13. Photosynthetic rate (Under optimal conditions (mgCO2/dm2/hour)- Variable and slow (0.5-0.7).
14. Biomass production- Low.
15. Presence of Photorespiration- Low.
16. Sensitivity to oxygen- Yes.
17. Water use Efficiency (No. of g. of H2O to produce 1 g. plant matter)- Very High.
18. Optimum temperature- Approx. 35°C.
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