carbon fixation

1. GUIDED BY:
DR. Trupti Patnaik Mam
H.O.D of Botany Department
Submitted by:
HARSHITA SAHOO
UNIVERSITY ROLL: 53RO117001
+3 3RD YEAR
C4 AND CAM PATHWAYS
OF
CARBON FIXATION
DEPARTMENT OF BOTANY
1
SEMINAR PROJECT

2. CERTIFICATE
This is to certify that the project on “C4 AND
CAM PATHWAYS OF CARBON FIXATION” submitted
by HARSHITA SAHOO of +3 3RD YEAR science,
ROLL NO.- 53RO117001 has been conducted under
my supervision and guidance to the best of my
knowledge. This is an original and interesting
piece of work and it represents the proper
classified and summarised view of the project.
signature
2

3. ACKNOWLEDGEMENT
I would like to express my gratitude to the out
standing group of who have helped me in completing my
project successfully. I would like to convey my sincere
regards to them for their indebted rendered to me at all
times.
I would like to H.O.D. DR. TRUPTI PATTANAIK to
guide me through the right path to the completion of my
project period. Finally I am very much indebted to my
parents for their moral support and encouragement to
achieve higher goals. I have no words to express my
gratitude towards my parents. Finally I would like to again
the outstanding group of people, the cable of supremely
positive individuals who have encouraged, pushed and
supported me throughout the long period of this project.
3

4. 4
Sl. No. Topics
1 Certificate
2 Acknowledgement
3 contents
4 History of C4 cycle
5 C4 plant names
6 What is C4 cycle
7 Why we need C4 cycle
8 Adaptations of C4 cycle
9 Bundle sheath cells & mesophyll cells
10 Steps of C4 cycle
11 Significance of C4 cycle
12 History of CAM pathway
13 CAM pathway plant names
14 Pathway of CAM during Night
15 Pathway of CAM during Day
16 A diagrammatic scheme for CAM pathway of
Co2 fixation
18 Types of CAM plants
19 Ecological significance of CAM plants
20 Bibliography

5. 5

6. History of C4 cycle
• In 1965, KORTSCHAK and his co-workers worked
on sugarcane found that the first stable production
of this plant is 4-carbon containing compound
aspartic acid or malic acid as a result of Co2 fixation.
• It was confirmed and greatly elaborated by HATCH
& SLACK who observed an alternative pathway
known as Hatch Slack pathway or C4 cycle in certain
separate plants like Saccharum officinarum, Zea
mays (maize), Cyperus rotundus, Amarantus etc.
• They reported that a 4-C compound oxaloacetic acid
(OAA) is the first stable product in Co2 reduction
process. This occurs only after 1 sec of photo
synthesis, which on long exposures forms 3- PGA.
• This led to an alternative pathway of Co2 fixation,
which is known as HATCH and SLACK’S cycle or
C4 cycle.
• This pathway was first reported in family
GEAMINEAE (grasses) but later on in other sub
tropical plants like ANGIOSPERMS.
6

7. C4 plants
names
1. Sugarcane
(Saccharum
officinarum)
2. Zea mays
(maize)
3. Sorghum
(Sorghum
bicolor)
4. Millets
5. Switchgrass
(Panicum
virgatum)
7

8. What is C4 cycle?
• C4 carbon fixation is a photosynthetic
process.
• A C4 plant is a plant that cycles carbon
dioxide into four-carbon sugar
compounds to enter into the Calvin cycle
(C3 cycle) .
• These plants are very efficient in hot,
dry climates and make a lot of energy.
• Many foods we eat are C4 plants like
corn, pineapple, and sugarcane.
• The C4 pathway is a physiological
specialisation of tropical plants that
accelerates photosynthesis by
concentrating carbon dioxide.
8

9. Why we need C4 cycle?
• Some plants which live in drought, at high
temperature and nitrogen and Co2 limitation
environment they use C4 mechanism.
• As the temperature rises, the oxygenase
activity of RUBISCO increases more rapidly
than the carboxylase activity.
• As C4 can fix more Co2 as compared to C3
plants due to having Kranz Anatomy.
• They also avoid photorespiration process.
9

10. Adaptation of C4 cycle
• Some plants are adapted to live in hot
climate for which plants have evolved a
mechanism to maximize the carboxylase
activity of RUBISCO.
• In such plants carbon fixation using
Calvin cycle takes place in bundle
sheath cells that are protected from the
air by mesophyll cells.
• Since the bundle sheath cells are not
exposed to air, the O2 concentration is
low.
• The Co2 is transported from the air via
mesophyll cells to the bundle sheath
cells by combining with 3-C molecule to
form 4-C molecule.
• These enter to bundle sheath cells where
they are broken down to C3 compounds
releasing Co2.
10

11. • The C3 molecules return to mesophyll cells to
accept more Co2 .
• This cycle ensures a high Co2 concentration
for the carboxylase activity of RUBISCO action
in the bundle sheath cell maintains a high
concentration of Co2 at the site of Calvin cycle.
• The 3-C compound pyruvate returns to the
mesophyll cell for another round of
carboxylation.
• Since it relies on Co2 transport via 4-C
molecules, it is called the C4 pathway and
plants that use this mechanism are called C4
plants.
11

12. BUNDLE SHEATH CELLS
AND
MESOPHYLL CELLS
• C4 pathway requires the presence of two
types of photosynthetic cells, i.e., mesophyll
cells and bundle sheath cells.
• The bundle sheath cells are arranged in a
wreath like manner.
• This kind of arrangement of cells is called
Kranz anatomy.
• In Kranz anatomy, the mesophyll and bundle
sheath cells are connected by
plasmodesmata.
• The C4 plants contain dimorphic
chloroplasts.
• The chloroplasts in mesophyll cells are
granal, whereas in bundle sheath cells they
are agranal.
• The granal chloroplasts contain thylakoids
which are stacked to form grana, as formed
in C3 plants.
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13. 13

14. • However, in agranal chloroplasts of bundle sheath
cells grana are absent and thylakoids are present
only as STROMA LAMELLAE.
• The presence of two types of cells allows
occurrence of light and dark reactions separately in
each type.
• Here, release of O2 takes place in one type, while
fixation of CO2 catalysed by Rubisco enzyme
occurs in another type of cells.
• In C4 plants (maize, sugarcane, etc.), light reactions
occur in mesophyll cells, whereas CO2 assimilation
takes place in bundle sheath cells. Such
arrangement of cells does not allow O2 released in
mesophyll cells to enter in bundle-sheath cells.
• Hence, Rubisco enzyme, which is present only in
bundle-sheath cells, does not come into contact
with O2, and thus, oxygenation of RuBP is
completely avoided.
• In C4 plants, a CO2 concentrating mechanism is
present which helps in reducing the occurrence of
photorespiration. This type of CO2 concentrating
mechanism is called C4 pathway.
14

15. THE STEPS OF C4 PATHWAY
• In C4 pathway, CO2 from the atmosphere
enters through stomata into the mesophyll
cells and combines with phosphoenol
pyruvate (3-carbon compound). This
reaction is catalysed by an enzyme known
as phosphoenol pyruvate carboxylase, i.e.,
PEP carboxylase. With the result, a
C4 acid, oxaloacetic acid (OAA) is formed.
15
Step I :

16. • Oxaloacetic acid is converted into
1. malic acid by an NADP+ linked malate
dehydrogenase and
2. into aspartic acid in presence of enzyme
transaminase.
16
Step II :

17. • From chloroplast of mesophyll cell, the
malic acid is transferred to chloroplast of
bundle sheath cells where it is
decarboxylated to form Co2 and pyruvic
acid in presence of NADP+ and specific
malic enzyme.
Step IV :
• Second carboxylation occurs in chloroplast
of bundle sheath cells. The released Co2 is
used in the carboxylation of ribulose-1, 5-
diphosphate in the presence of enzyme
CARBOXYDISMUTASE to produce
phosphoglycerate i.e. the Calvin cycle.
17
Step III :

18. • The pyruvic acid produced is transferred
to chloroplasts of mesophyll cells where
it is phosphorylated to regenerate
phosphoenol pyruvic acid by utilising
energy of ATP phase in presence of
enzyme Pyruvate Phosphate Dikinase.
• The Hatch Slack cycle occurs in mesophyll
cells while those of Calvin cycle occurs in
bundle sheath cells. The mesophyll and
bundle sheath cells are in contact with one
another. The C4 mode of photosynthesis is
less efficient in itself in comparison to C3
cycle.
18
Step V:

19. 19

20. Significance
of
Hatch Slack Pathway:
• This pathway is a modification of
Calvin cycle and is advantageous to
plants growing in dense stands of
tropical vegetation where the
CO2 concentration may be very much
reduced.
• There has been a reduction of atm.
CO2 concentration since the evolution of
photosynthesis and this might have
prompted C4 plants to select this
pathway.
• The discovery of this pathway has
indicated the existence of yet
undiscovered photosynthetic reactions
other than the conventional Calvin cycle.
20

21. 21

22. History of CAM pathway
• CAM was first suspected by de Saussure in 1804.
• The term CAM may have been coined by RANSON
and THOMAS in 1940, but they were not the first
to discover this cycle.
• It was observed in the succulent family Crassulaceae.
• Hence it is called Crassulacean acid metabolism.
• This type of metabolism, refers to a mechanism of
photosynthesis, that is, different from C3 and
C4 pathways.
• Crassulacean acid metabolism (CAM) is found only
in succulents and other xerophytes or plants that
grow in dry conditions.
• It is occurs in mostly succulents (xerophytes) like
Opuntia, Agave, Aloe, Sedum, Kalanchoe, etc.
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Sedum Crassulaceae red herb

23. CAM plants
names
1. Pineapple
2. Stonecrop
3. Spanish
moss
4. Jade plant
23

24. What is CAM Pathway?
• CAM pathway is a carbon fixation pathway in
some photosynthetic plants.
• Under natural conditions the acidity of green
shoots of some non-halophytic succulents and semi-
succulent plants increases at night and decreases
during the following day.
• It is found specially in plants living in arid
conditions or desert (for example cacti or
pineapple)
• CAM is yet another adaptation to increase
efficiency of the Calvin cycle.
• It is a response to drought as well as warm
conditions.
• In CAM the stomata of leaves are closed during the
day to avoid water loss.
• As a result Co2 cannot be absorbed during the day
hours when it is needed for glucose synthesis.
• When stomata opens at cooler temperature at
night, Co2 is fixed by C4 pathway into malate,
which is stored in vacuoles.
• During the day malate is decarboxylated and Co2
becomes available to the Calvin cycle.
24

25. CAM plants
names
1. Tree houseleek
2. Orchids
3. Agave
4. Cacti
25

26. Pathway of CAM
during Night
1. During night, starch, produced by
photosynthetic process, is broken down to
phosphoglyceric acid (PGA), through
glycolytic reactions.
2. PGA is then converted to PEP.
3. PEP is carboxylated by oxaloacetate by the
enzyme PEP case. As during night, stomata
are opened, hence Co2 enters the leaf
mesophyll cells and used for the
carboxylation of PEP.
4. Oxaloacetate is reduced to malate by
NAD- malate dehydrogenase. Male is
stored in the leaf mesophyll tissue in dark
during night which is further utilized during
day time.
Previously it was thought that double
carboxylation occurs for the production of PEP,
i.e., one carboxylation of RuBP to produce PGA
and another carboxylation of PEP to yield
oxaloacetate, because it was thought that PGA
was derived via RuBP carboxylation by RuBP
case (Ribulose bisphosphate carboxylase).
26

27. Pathway of CAM
during Day
• The stored malate in the dark during night in the
mesophyll cells of the leaf are again
decarboxylated during day as in C4 pathway of
photosynthesis.
• Direct carboxylation of malate takes place to
yield pyruvate which may occur either in
mitochondria or in cytoplasm.
• The pyruvate is then converted to PEP by
pyruvate Pi Dikinase located in chloroplast as in
C4 plants . The energy is supplied by ATP.
• The Co2 released after decarboxylation of
malate is utilized by Ribulose bisphosphate
(RuBP) to produce PGA by the action of enzyme
RuBP Case. PEP may also be converted to PGA.
• By C3 pathway PGA is ultimately converted to
hexose sugar and then to starch which is again
utilized in dark during night so that the CAM
cycle continues.
27

28. A diagrammatic scheme for CAM
pathway of Co2 fixation
Dark (night) Light (day)
28

29. Obligate CAM plants
• Opuntia basilaris
• Zygocactus
Facultative/ inducible
CAM plants
• Kalanchoe tubiflora
• Mesembryanthemu
m crystallinum
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30. Ecological Significance of CAM:
• CAM plants are especially suited to dry habitats such as
deserts. These plants have remarkable capacity to attain
high biomass under conditions of high evaporation rate or
scanty rainfall, which are otherwise insufficient for growth
of crop plants.
• Nocturnal opening of stomata in CAM plants allows uptake
of atmospheric CO2 when conditions for transpiration are
at a minimum. During day time, when stomata are closed
to check transpiration, photosynthesis can proceed by using
CO2 released from decarboxylation of malate. The
transpiration ratio (i.e., the ratio of the wt. of water
transpired to the wt. of dry matter produced) for CAM
plants is substantially lower than either with those of C3 or
C4 plants.
• Typically, a CAM plant loses about 50-100 gm. of water for
every gm. of CO2 gained, as compared with 250-300 grams
for C4-plants and 400-500 grams for C3-plants. Therefore,
CAM-plants have definite competitive advantage over
C3 and C4 plants in dry habitats such as in deserts. However,
rates for daily carbon assimilation in CAM plants are only
about half those of C3-plants and one third those of C4-
plants.
• Daylight closure of stomata in CAM plants to conserve
water in dry habitats, may not be the unique basis for
evolution of CAM. It is because, paradoxically, some aquatic
plant species are also known to exhibit CAM. According to
some scientists, CAM probably also increases acquisition of
inorganic carbon in the form of bicarbonate ions (HCO3
–) in
aquatic habitats, when availability of CO2 is restricted due
to high resistance to gas diffusion.
30

31. BIBLIOGRAPHY
• www.biologydiscussion.com
• www.wikipedia.org
• https://goo.gl/GU7xEZ
• https://www.google.com/search?q=khan+academ
y&rlz=1C1RLNS_enIN859IN859&oq=khan+ace&aq
s=chrome.1.69i57j0l7.3445j1j8&sourceid=chrome
&ie=UTF-8
• https://libgen.is/search.php?req=Cscl2+gradient&
open=0&res=25&view=simple&phrase=1&column
=title
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