2. Submitted to: SIR ZAFAR IQBAL
2
DEPARTMENT OF BOTANY
UNIVERSITY OF SARGODHA
3. Plant Evolutionary
History
Life began in water
The earliest plants were aquatic
• Since plants evolved to live without
water, they had a hard time dealing
with dehydration
3
4. Plants
adaptations
Most adaptations involve in some
sort of trade off.
For plants the trade off with
photosynthesis is that they lose
water to the environment through
transpiration.
4
5. 5
The openings on leaves is called
stomata.
This is where 𝐶𝑂2 and 𝑂2 can enter
and exit the plant.
Water is also lost through stomata.
Plants often close stomata in very hot
days, and also 𝐶𝑂2 intake cuts off.
A little plant anatomy
6. 6
Those plants whose first product of
photosynthesis is 3 carbon compound.
About 85% of plant species are 𝑪 𝟑 plants.
The term 𝑪 𝟑 photosynthesis is ancestral
pathway for carbon fixation.
It occurs in all taxonomic plant groups.
The term 𝑪 𝟑 photosynthesis is based on the
observations that the first product of
photosynthesis is a 3-carbon molecule.
In this way such plants are known as
𝑪 𝟑 plants.
𝐶3 Plants
7. 7
In 𝑪 𝟑 plants, the bundle sheet cells do
not contain chloroplast
Carbon dioxide fixation takes place
only at one place.
𝐶3 Plants
8. 8
𝑪 𝟑 photosynthesis is the major of
three pathways for carbon fixation by
plants.
During hot days they close their
stomata part way and produce little
sugar.
𝐶3 Mechanism
9. 9
And send it to the Calvin cycle
instead of 𝐶𝑂2
Peroxisomes and mitochondria split
the new compound and release 𝐶𝑂2
This is called photorespiration.
s the 𝐶𝑂2 is used up by plant, rubisco
fix 𝑂2 instead
10. 10
Photorespiration uses ATP but
don’t make ATP.
Photorespiration makes no
sugar
Photorespiration decreases
photosynthesis output.
11. 11
Photorespiration may be an evolutionary leftover
In early atmosphere, with little 𝑂2 it didn’t matter if
rubisco had an affinity for 𝑂2
Today with so much 𝑂2 in the atmosphere, it is inevitable
that some 𝑂2 will be fixed in the environment.
So why would any plant do
this…
12. 12
o They include cereals, grains, wheat,
rice. Barley, oats, peanuts, cotton,
sugar beets, tobacco, spinach,
soybeans and most trees are 𝑪 𝟑
plants.
o Most lawn grasses rye and fescue are
𝑪 𝟑 plants.
𝐶3 Crop Plants
13. 13
The plant whose first product of
photosynthesis is 4 carbon compound is
called C4 plant.
Those plants which undergo 𝐶4
photosynthesis are known as 𝐶4 plants.
𝐶4 photosynthesis occur in more advanced
plant taxa and specially common among
dicots(most trees and shrubs).
𝐶4 plants evolved independently in a hot, dry
environment where their stomata must be
partially closed during the day.
𝐶4 Plants
14. 14
In 𝐶4 plants the bundle sheet cells
contain chloroplasts.
Carbon dioxide fixation takes place
twice (one in mesophyll cells, second in
bundle sheath cells).
In 𝐶4 photosynthesis the initial
photosynthetic product is 4-carbon
molecule.
𝐶4 Plants
15. 15
Why plant use C4 mechanism ?
Some plants which live in drought, at high temperature and
nitrogen and carbon dioxide limitation environment, they use C4
mechanism
Because C4 plants fix more carbon dioxide as compared to C3
plants due to having KRANZ anatomy
C4 plants lose 277 molecules of water to fix per molecule of CO2
as compared to c3 use 833 molecules of water approximately at
30°C
They also avoid photorespiration process
C4 enzyme fix carbon more efficiently as compared to C3 plants
who also fix oxygen during carbon fixation process
16. 16
Why plant use C4 mechanism ?
Fixation of oxygen starts the process of photorespiration instead of
carboxylation of substrate, substrate oxidize and as a result loss
and start the process of photorespiration.
This process occur due to the dual activity of rubisco present in C3
plants such as oxygenase and carboxylase activity.
17. 17
KRANZ ANATOMY
Their vascular bundles are surrounded by the two ring cells
Inner ring
Contain bundle sheath cells (bundle sheath cells contain starch rich
chloroplast lacking grana)
Outer ring
Contain mesophyll cells
18. 18
ADVANTAGES OF KRANZ ANATOMY
Main function of Kranz
anatomy is:
• To provide a site in which
CO2 concentrated around
rubisco
• And avoiding
photorespiration mechanism
19. 19
MECHANISM OF C4 PLANTS
FIRST STEP:
Conversion of (PEP) into oxalo-acetic acid
In this step CO2 react with phosphoenol pyruvic acid to
form oxaloacetic acid
This reaction takes place in the presence of enzyme
phosphoenol pyruvate carboxylase
20. 20
MECHANISM OF C4 PLANTS
2nd STEP:
Conversion of OAA into Malate
In this step oxaloacetic acid is converted into Malate
This reaction is catalyzed by malate dehydrogenase.
21. 21
MECHANISM OF C4 PLANTS
3rd STEP:
Conversion of Malate into pyruvic acid
In this step malate is transported into bundle sheath cell.
In bundle sheath cells it is converted into pyruvic acid by
releasing CO2
22. 22
MECHANISM OF C4 PLANTS
4th STEP:
Conversion of pyruvic acid into PEP
In this step pyruvic acidreacts with ATP and regenerate
phosphoenol pyruvate.
This reaction takes place in the presence of pyruvate
orthophosphate dikinase.
24. 24
𝐶4 photosynthesis is an adaptation for
plants living in hot, arid climate
Some plants that live in hot, dry climates
maintain low oxygen levels in their leaves
by keeping stomata closed to prevent
water loss.
𝐶4 plants have special leaf anatomy with
prominent bundle sheath cells
surrounding the leaf veins.
𝐶4 Adaptations
25. 25
𝐶4 plants have
adaptations that allow
them to minimize the
effect of photorespiration.
𝐶4 Adaptations
26. 26
They have an alternate
means of fixing carbon.
𝐶4 plants fix carbon out in
the cytoplasm before it
enters the Calvin Cycle
27. 27
They have special type of
leaf anatomy
They tolerate high
temperatures.
They show response to
high light intensities.
28. 28
The large cells present
around the vascular
bundle of the 𝐶4 pathway
plants are known as
bundle sheath cells.
The leaves which have
such anatomy are said to
have KRANZ anatomy.
Bundle Sheath
Cells
29. 29
𝑪 𝟒 Plants undergo
𝑪 𝟒 cycle which is
also known as
Hatch And Slack
cycle.
Hatch and slack cycle
30. 30
1st step is binding 𝐶𝑂2 to PEP (Phosphoenolpyruvate) by enzyme PEP
carboxylase to make a 4-C compound
PEP has a high affinity of 𝐶𝑂2 and none for 𝑶 𝟐
The 4-Carbon compound enters the photosynthetic cells.
𝑪𝑶 𝟐 is released from PEP and Calvin cycle continues as normal
𝐶4 Plant Adaptation
s
31. 31
They have greater productivity in biomass.
Despite having Oxaloacetic acid as the first 𝐶𝑂2 fixation product
they use 𝑪 𝟑 pathway or Calvin cycle as the main biosynthetic
pathway
𝐶4 plants have twice as the photosynthetic capacity as 𝐶3 plants
and can cope with higher temperature, less water and available
nitrogen.
32. 32
𝐶4 plants thrive in hot
climate where stomata
will be closed often
Some important 𝐶4
plants are sugarcane,
corn, tropical grasses
33. 33
This adaptation allows 𝐶4 plants
to keep a high concentration of
𝐶𝑂2 in the photosynthetic cells,
preventing from building of 𝑶 𝟐
instead of 𝐶𝑂2
34. 34
They include black mustard seed,
watercress, lettuce, cabbage,
maize, sorghum, millets, switch-
grass, broccoli, cauliflower, turnip
etc.
𝐶4 Crop Plants
35. COMPARISON
𝑪 𝟑 Plants
Photosynthesis occur in mesophyll
tissues
• The carbon dioxide accepter is
RuBisco
• KRANZ anatomy is absent
• The 1st stable compound formed is
3C compound called 3-
phosphoglyceric acid (PGA).
𝑪 𝟒 Plants
Photosynthesis occurs both in
mesophyll and bundle sheath cells.
The carbon dioxide acceptor is
PEP carboxylase.
KRANZ anatomy is present
The 1st stable compound is 4-
carbon Oxaloacetic acid (OAA)
35
36. COMPARISON
𝑪 𝟑 Plants
The optimum temperature is 20 -
25°C.
Photo-respiratory loss is high.
Photosynthetic rate is low.
They are more adapted to
environment with more carbon
dioxide.
𝑪 𝟒 Plants
The optimum temperature is 35 –
44°C.
Photorespiration does not takes
place.
Photosynthetic rate is comparatively
high
They are more adapted to
environment with more oxygen.
36
37. 𝑪 𝟑 Plants 𝑪 𝟒 Plants
Most plants Tropical grasses like
corn, sugarcane
Fix carbon in Calvin cycle –
attach 𝐶𝑂2 to RuBP
Fix carbon in cytoplasm
- attach 𝐶𝑂2 to PEP
Enzyme - Rubisco Enzyme – PEP-ase
Most energy efficient
method Less efficient
Lose water through
photorespiration Lose less water
Comparison
of 𝐶3 & 𝐶4 Plants
37
38. 38
CARBON FIXATION
C4 pathway is certainly more efficient than C3 pathway in
sense of carbon fixation.
The enzyme responsible for this step is rubisco
In C4 plants the inner cells get only carbon dioxide in the form
of malate.
This avoid the oxygenation process and hence makes the
pathway more efficient
39. 39
Why is C3 photosynthesis inefficient
C3 plants have disadvantage that in hot dry conditions their
photosynthetic efficiency suffers because of processes
called photorespiration.
When CO2 concentration in chloroplast drops below about
50ppm, the catalyst rubisco helps to fix carbon begin to fix
oxygen instead
43. Significance of 𝑪 𝟒 Plants
43
In 𝑪 𝟒 plants, it increase the
photosynthetic yield two to three
times more than 𝑪 𝟑 plants
In 𝑪 𝟒 plants, it performs a high rate
of photosynthesis even when the
stomata are nearly closed.
It increases the adaptability of 𝑪 𝟒
Plants to high temperature and
light intensities.
They can grow very well in saline
soils because of presence of 𝑪 𝟒
organic acid.