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 CO2 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 CO2 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 CO2 fixation into carbohydrates occurs by
Calvin cycle that completes in bundle sheath cells.
The mesophyll cells provides enough concentration of CO2
to fix it.
In this cycle every CO2 molecule fixed twice 1st in
mesophyll cell and 2nd in bundle sheath cell.
In mesophyll cell the primary acceptor of CO2 is ,
Phosphoenolpyruvate it traps CO2 and form 1st stable
product OAA (Oxaloacetic acid) with the help of
PEPCarboxylase.
PEP +CO2 → OAA

7. The formed OAA is reduce to Malate with in
mesophyll cell, the energy required for this, is
supplied by NADPH2.
The enzyme is Malate dehydrogenase.
OAA + NADPH2 → 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 CO2.
The enzyme is Malate enzyme
Malate +2NADP → Pyruvate+CO2↑+NADPH2

8. Here released CO2 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 CO2
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 CO2 pool.

12. C3 CYCLE
1. C3cycle occurs in all
plants.
2. It is a common pathway
in plants.
3. Occurs in mesophyll
cells.
4. Primary CO2 acceptor is
RUBP, a 5C compound.
C4 CYCLE
1. C4cycle occurs only in
C4 plants.
2. It is a adaptive pathway
in plants.
3. Occurs in mesophyll
and bundle sheath
cells.
4. Primary CO2 acceptor is
PEP, a 3C compound.

13. 5. First stable product is a 3C
compound 3PGA(3-
Phosphoglycerate).
6. Single CO2 fixation.
7. The carboxylase enzyme is
RUBisCO.
8. CO2 fixation is slow and less
efficient because RUBisCO
can bind with O2.
5. First stable product is OAA
(Oxaloacetic acid) a
4Ccompound.
6. Each CO2 molecule fixed
twice .
7. Carboxylase enzyme are PEP
carboxylase and RUBisCO.
8. CO2 fixation is fast and
more efficient because PEP
has more affinity to CO2.

14. 9. Fixation of 1 CO2 requires 3
ATP and 2 NADPH2.
10. Can not operate under low
CO2 concentration.
11. O2 has inhibitory effect on
photosynthesis.
12. Photorespiration occurs
fastly.
13. Required 18ATP to form 1
molecule of Glucose.
14. Less yield through this
cycle.
9. Fixation of CO2 requires
5ATP and 2NADPH2.
10. Can operate under low CO2
concentration.
11. O2 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.