C3 and C4 plants transitions adaptations of C3 plants to C4 plants what are C3 and C4 plants

1. Evolutionary
Transitions from C3 to
C4 plantsSUBMITTED BY: HAFSA ARSHAD
ROLL NUMBER: BBOF17M006

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

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 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

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In 𝑪 𝟑 plants, the bundle sheet cells do
not contain chloroplast
Carbon dioxide fixation takes place
only at one place.
𝐶3 Plants

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 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

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 Photorespiration uses ATP but
don’t make ATP.
 Photorespiration makes no
sugar
 Photorespiration decreases
photosynthesis output.

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 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…

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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

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 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

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 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

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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

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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.

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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

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ADVANTAGES OF KRANZ ANATOMY
Main function of Kranz
anatomy is:
• To provide a site in which
CO2 concentrated around
rubisco
• And avoiding
photorespiration mechanism

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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

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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.

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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

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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.

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C4 MECHANISM

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 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

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 𝐶4 plants have
adaptations that allow
them to minimize the
effect of photorespiration.
𝐶4 Adaptations

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 They have an alternate
means of fixing carbon.
 𝐶4 plants fix carbon out in
the cytoplasm before it
enters the Calvin Cycle

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 They have special type of
leaf anatomy
 They tolerate high
temperatures.
 They show response to
high light intensities.

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 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

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𝑪 𝟒 Plants undergo
𝑪 𝟒 cycle which is
also known as
Hatch And Slack
cycle.
Hatch and slack cycle

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 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

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 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.

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 𝐶4 plants thrive in hot
climate where stomata
will be closed often
 Some important 𝐶4
plants are sugarcane,
corn, tropical grasses

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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

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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)
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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

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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

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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

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Leaf Anatomy Of 𝐶3 & 𝐶4 Plants

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𝐶3 & 𝐶4 cycles

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43. Significance of 𝑪 𝟒 Plants
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 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.

44. THANK YOU!
Email
hafsaranjha.botanist@gmail.com