This Presentation covers some content on "Photosynthetic performance and crop productivity in response to climate change" based on some published papers

1. Ayesha Siddiqui
Botany
University of Agriculture, Faisalabad

2. Potential for increased photosynthetic performance
and crop productivity in response to climate change:
role of CBFs and gibberellic acid
 Norman P. A. Hüner1, Keshav Dahal, Leonid V.
Kurepin1, Leonid Savitch, Jas Singh, Alexander G.
Ivanov, Khalil Kane and Fathey Sarhan
 It was published on April 2014 in FRONTIERS IN
CHEMISTRY

3. Impact of climate change on crop
productivity
Increased severity of stresses
Altered global climate
(sub-opt condition for
plant growth
Enhanced CO2
concentration
Drastic
temperature
changes
Urbanization
Industralization
Desertification
1.Photosynthetic performance
2. Biomass production
3. Crop seed yield

4. Green
revolution
Short, sturdy semi-dwarf
High HI & low tendency to lodge
Ultimate solution
Increased efficiency
of photosynthesis
required

5. Major concerned
Increasing population results in increased food
demand
To supplement increased food demand
by using any approach that is helpful
Improved agricultural
techniques
Improved genetic
techniques

6. Targeted genetic approaches for
improving yield
 To alter the structure & composition of the
photosynthetic photosystems and their
associated antenna complexes,
 To alter the structure of the CO2 fixing enzyme,
Rubisco, in order to reduce the rates of
photorespiration in C3 crop plants
 To increase the potential for C4 photosynthesis
in C3 plants such as rice

7. Proposal for improving yield:
cold acclimation
Cold acclimation is a novel approach to enhance plant
biomass production
1. by co-ordinating source-sink demand
2. And minimizing energy loss through NPQ
3. And enhanced over-expression of CBFs increases
1. Increased photosynthetic performance
2. Increased WUE
3. Potential for enhanced resistance to biotic stress
Leads to enhanced photosynthetic performance

8. Maximum potential biomass and grain
yield determinant
1
• Incident solar radiation
2
• Translocation of photosynthates to sink
3
• Partioning efficiency i.e. HI
4
• Light interception efficiency
5
• Energy conversion efficiency

9. Energy conversion efficiency
 is, the ratio of the biomass energy produced over a
given period to the radiative energy intercepted by the
canopy over the same period.
Theoretically, increasing this
efficiency will increase potential
biomass

10. Hypothesis: Maximum energy conversion
into biomass may improve yield
 Plant body Carbon 40% dry mass
Increase

11. Crucial
photoprotective mechanism
reduces yield

12. Photoprotective mechanism
reduces yield
absorbed energy
Photosynthetically
generated electrons
by C,N & S metabolism
Transformed into
reducing power
Excess energy is
dissipated

13. Photoprotective mechanism
is crucial
Protects
Photosynthetic apparatus
from irradiance
 Which is more than what
can be used by reductive
CO2, N & S assimilation

14. Need for Photoprotective Mechanism
Reduces efficiency of
CO2 assimilation as
energy is dissipated, as a
result less biomass
Reduction of this process
may increase
CO2 assimilation
Necessary evil for plant
survival against
environmental stresses

15. Proposal: Cold acclimation is
the solution
 Phenotypic plasticity, increased photosynthetic
surface
 Ultimately increased photosynthetic performance
 Minimizes dependance on NPQ for photoprotection
 Enhanced photosynthetic performance at elevated
CO2 and maintained during long term growth
 Inherent resistance to abiotic as well as biotic stress

16. Cold acclimation improves
photosynthetic performance
•It is estimated that under optimal growth
conditions only about 4.6% of the initial energy
that impinges the leaf surface is conserved as
fixed carbon and plant biomass.
•Suboptimal conditions may increase Carbon
assimilation in cold acclimated cultivars.

17. Winter CA or semi-dwarf
cultivars
Made by?
gai mutant
GAI controlled
i.e.
Gibberellins
responsive
transcription
factors

18. Winter CA cultivar
Rye, Barley etc
1. Enhanced Carbon metabolism
2. Enhanced sink capacity
3. Enhanced Pi cycling
4. Increased capacity for RUBP regeneration
5. Reduces photorespiration
6. Stimulates Carbon export from leaf
Conclusion:-
Co-ordinate system that
1. Enhances source-sink activities
2. More CO2 assimilation

19. 1
• Increased cytosolic sucrose
biosynthetic enzymes i.e. SPS etc
2
• Increased gene expression
3
• Controlled RubisCO activities
Enhanced Carbon
metabolism

20. Enhanced sink
capacity
Crown leaf mesophyll
tissue cell vacoule
Sucrose export
Stored as fructans in

21. Cold acclimation & phenotypic
plasticity
 Regulated by redox state of chloroplast measured
as excitation pressure
Chloroplast redox signal
Regulates

22. Excitation pressure
is defined as a quantitative measure of
the proportion of closed PSII reaction
centers due to an imbalance between
energy absorbed vs. energy either utilized
through metabolism and growth or
dissipated as heat.

23. Picture explained
 Accumulation of growth-inactive GAs maintains levels
of DELLA proteins such growth and stem elongation
are repressed which generates a dwarf phenotype.
 This dwarf phenotype exhibits enhanced
photosynthetic performance and increased dry
biomass per unit plant volume coupled with enhanced
seed yield in CA wheat

24. CA dwarf phenotype results in improved
photosynthetic performance
Altered leaf
mesophyll cell
ultrastructure
Increase in
cytoplasmic volume
Decrease in
vacuolar volume
Increased specific
leaf weight
Increased leaf thickness
Increased mesophyll cell
size
Increased palisade
mesophyll layers
1. Increased leaf protein content
2. increased sucrose & other
structural carbohydrate

25. Larger extended
phenotype results in
Autumn (cold period)
• Increased total energy per unit plant
volume
Following spring
• Enhanced seed yield

26.  Extended Phenotype
 Increased leaf area
 Increased photosynthetic apparatus per unit leaf area
 Increased capacity to utilize absorbed light energy
 Keeps PSII reaction centers open
 Lowers excitation pressure
 Less photoinhibition of photosynthesis

27. Cold acclimation reduces relative
dependence on NPQ
Efficiency
light utilization for CO2
assimilation
Energy dissipation
as the apparent number of
photons required to close
50% of PSII reaction
centers
as the apparent number of
photons required to induce
one unit of NPQ

28. Shifting C3 to C4: short term increase in
CO2 assimilation
 It has been established that a short-term shift of C3
species from ambient to elevated CO2 results in an
increase in the rates of CO 2 assimilation
 This stimulation of photosynthesis in C3 plants due to
elevated CO2 occurs because Rubisco is CO2 substrate
limited at ambient CO2 and photorespiration is
suppressed since CO2 is a competitive inhibitor of the
oxygenation of RuBP by Rubisco

29. Shifting C3 to C4: Feed back inhibition
at long term exposure to CO2
Long-term growth and development of C3 plants at high
CO2 may lead to end product inhibition of
photosynthesis due to the accumulation of sucrose in
the cytosol.
This feedback inhibition of growth at elevated CO2
levels is
1. Due to chloroplast Pi limitations
2. And down regulation of the expression and
activities of key regulatory photosynthetic
enzymes

30. Long term growth at elevated CO2:
Cold acclimation maintains
photosynthetic performance
 However, CA maintains their superior photosynthetic
performance with respect to light and CO2 saturated
rates and do not exhibit feedback inhibition of
photosynthesis at elevated CO2.
How does it do that?

31. Cold acclimated cultivar
gives better yield
35–50% decrease
in excitation
pressure & non-
photochemical
energy dissipation

32. Cold acclimated cultivar
gives better yield
Genes upregulated
for
maintenance of
chloroplast
stability
(chaperonins)

33. Cold acclimation regulates expression
of CO2 at molecular level
 plant cell membrane is the primary site that
determines the potential of plants to freezing
tolerance
 Low temperature activates Ca2+ channels and rapidly
generates a Ca2+signal that activates a cytosolic
protein kinase whose substrate is ICE1.
 The phosphorylation of ICE1 is required for the
induction of a family CBF transcription factors which
regulate the expression of CO2.

34. Benefits of cold acclimation
 enhanced photosynthetic performance
 superior resistance to photoinhibition
 suppresses stomatal conductance due to to a
decrease in leaf stomatal density
 reduces transpiration rates by 30–40%
regardless of the measuring temperature
 3- fold increase in leaf water use efficiency
(WUE) primarily due to a combination of a
decrease in stomatal density combined with the
observed increase in light saturated rates of
photosynthesis
 increased systemic resistance to plant infection

35. Conclusion of proposal research
Cold acclimation of winter rye, winter wheat, and
Brassica napus establishes a new homeostatic state
which is characterized by an increased
 photosynthetic capacity for CO2 assimilation
 and its conversion into biomass or energy per unit
plant volume
 and seed production in wheat under suboptimal
growth conditions

36. So we predict that cold acclimation not only
1. Enhances photosynthetic
performance
2. It also enhances inherent resistance
to biotic stress.

37. CBF family of
transcription factors
 Targeting the CBF family of transcription factors in
major crop species improves crop productivity through
increased photosynthetic performance, WUE and
resistance to abiotic stress

38. Potential role of CBFs
 CBFs results in enhanced dwarf phenotype by
decreasing level of growth active GAs
 CBFs overexpression is related with changes in cell
membrane structure (lipid and fatty acid composition
and contents) requires for acclimation to low
temperature
 CBFs regulates the expression of COR genes encoding
maxmium freezing tolerance.
 CBFs affects plant development
 CBFs regulates genes associated with photosynthesis,
respiration and cytosolic carbon metabolism

39. Suboptimal conditions associated with future
climate change (cold climate)
Overexpression of C/repeat dehdration responsive
family of transcription factors
Enhanced photosynthetic performance
Overexpression of CBFs circumvents the requirement
of cold acclimation

40. CBFs expression signals
emanates from Chloroplast
 Chloroplast is the cellular energy sensor for detecting
changes in the environment
 Chloroplast redox imbalance or excitation pressure
sends operational signals for CBFs expression
 However, it must be integrated with regulation
associated changes in light quality sensed through
photoreceptors such as phytochrome as well as
through specific cell membrane, low temperature
sensors to establish a new CA homeostatic state.

41. Drawbacks of proposed research
 Delayed flowering time
 Low temperature of CBF induction causes activation
of expression of FLC (flowering locus L), negative
regulator of flowering
 Delayed bolting
 Overexpression of AtCBF3 delays onset of bolting at
20 celsius by 4 to 9 days.
 Reduced seed yield
 CBF overexpressors have reduced seed yield at warm
temperatures.
 Spring Vs. winter cultivar
 Spring varieties don’t exhibit phenotypic change
so photosynthetic performance appears to be
cultivar dependant