C4 pathway

In some plant species, alternate modes of carbon fixation have evolved that minimize photorespiration and optimize the calvin cycle.

1. C4 PATHWAY DEFFERENCE Between C3 pathway and C4 pathway Submitted By Ms. PRIYANKA KUMAWAT M. Sc. Previous BOTANY S.S.G.PAREEK P.G. COLLEGE Submitted to: Department of Botany

2. C4 CYCLE / HATCH AND SLACK PATHWAY It is a different kind of CO 2 fixation (dark reaction) in some plant . It is also a cyclic pathway and the first stable product of this cycle is a 4c compound (OAA). DISCOVERY OF CYCLE In sugercane leaf H.P. Korts-chak ,C.E. Hart and G.O.Burr First reported that the first stable product of CO 2 fixation Is a 4c compound .

3. In 1966 M.D.Hatch and C.R.Slack discover the pathway of C4cycle and also the site. In their honor this cycle also called Hatch and Slack pathway. They certify that the first stable product is OAA ( Oxaloacetic Acid). C4 pathway occurs in C4 plant which grow in tropical region. The first product is a C4 compound but the synthesis of carbohydrates occurs by C3 cycle ( calvin cycle).

4. KRANZ ANATOMY OF LEAF ( C4 PLANT) The C4plants have a specific leaf anatomy called kranz anatomy. Their vascular bundle are surrounded by two rings of cells --- The inner ring called Bundle Sheath cell, contain large size agranal chloroplast. The outer ring is made up of mesophyll cells ,contain granal chloroplast. The wall of bundle sheath cells are impermeable for gas molecules.

5. Some example s of C4plants---- Monocote ( sugercane,maize etc.) Dicote (Mango ,Apple etc.)

6. C4cycle takes part in both mesophyll cell and bundle sheath cells. Also in C4plants CO 2 fixation into carbohydrates occurs by Calvin cycle that completes in bundle sheath cells. The mesophyll cells provides enough concentration of CO 2 to fix it. In this cycle every CO 2 molecule fixed twice 1 st in mesophyll cell and 2 nd in bundle sheath cell. In mesophyll cell the primary acceptor of CO 2 is , Phosphoenolpyruvate it traps CO 2 and form 1 st stable product OAA ( Oxaloacetic acid ) with the help of PEPCarboxylase . PEP +CO 2 → OAA

7. The formed OAA is reduce to Malate with in mesophyll cell, the energy required for this, is supplied by NADPH 2 . The enzyme is Malate dehydrogenase . OAA + NADPH 2 → Malate From mesophyll cell the Malate moves into bundle sheath cell through plasmodesmata . Within the bundle sheath cell malate oxidatively decarboxylated into pyruvate and release CO 2 . The enzyme is Malate enzyme Malate +2NADP → Pyruvate+CO 2↑ +NADPH 2

8. PEP Here released CO 2 acceptes by RUBP and under goes in C3 cycle. Pyruvate moves back to mesophyll cell to regenerate PEP. Pyruvate PEP The enzyme is Pyruvate dikinase . This prosses utilizes 2 molecule of ATP. This regenerted PEP is avilable to fix another CO 2 molecule. Thus cycle runs continuously.

9. C4 CYCLE

10. Dfference between C3 and C4 cycle C3 PLANTS C3 plants mainly + nt in wet soil. C3 plants only have C3cycle. KRANZ anatomy of leaf is –nt. C3 cycle oprates in mesophyll cell, because RUBisCO + nts in these cells. C4 PLANTS C4 plants + nt in tropical region adapt high light and temperature. C4 plants have both cycle C3 and C4. KRANZ anatomy of leaf is +nt. C3cycle oprates in bundle sheath cell ,due to + ance of RUBisCO in these cells.

11. Have no adaptation to minimize photorespiration. Low rate of photosynthesis due to high photorespiration. Have adaptation as C4cycle to minimize photorespiration. High rate of photosynthesis due to CO 2 pool.

12. C3 CYCLE C3cycle occurs in all plants. It is a common pathway in plants. Occurs in mesophyll cells. Primary CO 2 acceptor is RUBP, a 5C compound. C4 CYCLE C4cycle occurs only in C4 plants. It is a adaptive pathway in plants. Occurs in mesophyll and bundle sheath cells. Primary CO 2 acceptor is PEP, a 3C compound.

13. First stable product is a 3C compound 3PGA(3-Phosphoglycerate). Single CO 2 fixation. The carboxylase enzyme is RUBisCO . CO 2 fixation is slow and less efficient because RUBisCO can bind with O 2 . First stable product is OAA ( Oxaloacetic acid) a 4Ccompound. 6. Each CO 2 molecule fixed twice . Carboxylase enzyme are PEP carboxylase and RUBisCO . 8. CO 2 fixation is fast and more efficient because PEP has more affinity to CO 2 .

14. Fixation of 1 CO 2 requires 3 ATP and 2 NADPH 2 . Can not operate under low CO 2 concentration. O 2 has inhibitory effect on photosynthesis. Photorespiration occurs fastly . Required 18ATP to form 1 molecule of Glucose. Less yield through this cycle. 9. Fixation of CO 2 requires 5ATP and 2NADPH 2 . 10. Can operate under low CO 2 concentration. 11. O 2 has no inhibitory effect on photosynthesis. 12. Minimize the rate of photorespiration. 13. Required 30ATP to form 1 molecule of Glucose. 14. High yield through this cycle.