3. • The transduction of the energy of sunlight to
chemical energy by green plants is called as
photosynthesis.
6CO2 + 6H2O C6H12O6 + 6O2
Two types of reactions in photosynthesis
• Light dependent reactions
• Light independent reactions
3
Photosynthesis
5. The light dependent reactions
• Occur in the thylakoid membrane
• Converts light energy to chemical energy
• Chlorophyll and several other accessory pigments are
involved
• Final products
– NADPH
– ATP
– O2
5
6. Light independent reactions – The fixation
of CO2
• Take place in the stroma within the chloroplast
• Converts CO2 to sugar
• Involves the Calvin cycle
• Two basic types of photosynthetic mechanisms
– C3
– C4
6
7. Calvin cycle
• Chemical energy harvested by the light dependent
reactions, used to reduce carbon (CO2)
• The Calvin cycle consists of three main parts
– Carboxylation
– Reduction
– Regeneration
7
9. Four Carbon (C4) pathway
• In some plants, the first product of CO2 fixation is not the
three-carbon molecule 3-PGA, but four-carbon molecule
oxaloacetate (OAA).
• The C4 photosynthetic carbon cycle is an elaborated addition
to the C3 photosynthetic pathway.
• It evolved as an adaptation to
– high light intensities
– high temperatures
– suppress photorespiration
– increase carbon gain (Edwards et al., 2010)
• Associates with the Kranz anatomy
9
10. Kranz anatomy
• Thereby,
– Oxygenase reaction and the following photorespiration are repressed
– Rubisco accumulates in BSCs chloroplasts
– phosphoenolpyruvate carboxylase (PEPC) accumulate in the cytoplasm and
chloroplasts of MCs
– MCs and BSCs show differences in the biochemistry of carbon fixation.
– Division of labor achieved (Hatch, 1987)
10
Diagram of C4 leaf cross section
• Wrapping of vascular bundles by two specialized cell types, the mesophyll cells (MCs)
and bundle sheath cells (BSCs)
• To concentrate CO2 around Rubisco
11. 11
Leaf cross section of Panicum miliaceum, which exhibits Kranz anatomy
Mesophyll cell
Bundle sheath cell
(Source: http://sydney.edu.au/science/biology/learning/plantform_function/revisionmodules/2003A_
Pmodules/module1/1C9.shtml)
12. 12
An electron micrograph of grana- deficient chloroplasts in bundle sheath
cells and granal chloroplasts in mesophyll cells.
(Source: http://teosinte.uoregon.edu/cp_biogenesis/)
Mesophyll cell chloroplast
(Granal chloroplast)
Bundle sheath cell chloroplast
(Grana deficient Chloroplast)
Starch granule
Grana
13. The C4 pathway consists of three key steps
1. Initial fixation of CO2 by phosphoenolpyruvate carboxylase
(PEPC) to form a C4 acid
2. Decarboxylation of a C4 acid to release CO2 near the site of
the Calvin cycle
3. Regeneration of the primary CO2 acceptor
phosphoenolpyruvate (PEP)
13
14. 14
A diagram showing a summary of metabolic division of labor in mesophyll cells
and bundle sheath cells of C4 plants
Mesophyll cell Bundle sheath cell
1 2
3
15. Single cell C4 photosynthesis
• Kranz type leaf anatomy was synonymous with C4
photosynthesis.
• Single cell C4 photosynthesis lacks Kranz anatomy.
• Two types
1. Terrestrial single cell C4 photosynthesis
2. Aquatic single cell C4 photosynthesis
15
17. The family Chenopodiaceae
• A family of flowering plants, also called the Goosefoot Family.
• Contains approximately 1300 species worldwide and range
from annual herbs to trees.
• Majority are weeds and many are salt and drought tolerant.
• Many chenopod species have C4 photosynthesis.
17
18. Bienertia cycloptera
• Widespread in Central Asia
• Grows in salty depressions
• Plant is usually shorter, precise measurements are not
available.
• Flowering time is from July to August and fruiting period
is in September
A photograph of Bienertia cycloptera
18
19. Bienertia sinuspersici
• Distribution is restricted to Persian Gulf areas and Baluchistan
• Plant height is up to 130-160 cm
• Flowering time is October and fruiting period is from
November to December
A photograph of Bienertia sinuspersici
19
20. Suaeda aralocaspica
• Restricted to the deserts of central Asia
• It is a monoecious, annual, halophyte.
• Grows to a height of between 20- 50 cm
A photograph of Suaeda aralocaspica
20
21. • Lacks Kranz anatomy
• Compartmentalization of organelles and photosynthetic
enzymes into two distinct regions within a single cell
• Cytoskeleton associates with the positioning of chloroplasts
and other organelles
• Lack of night time CO2 fixation
• Function with a unique C4 mechanism
21
Features of single cell C4 photosynthesis
22. Cell compartmentalization (1)
• In Suaeda aralocaspica
– Two chloroplast types are arranged in cylindrical chlorenchyma cells.
– Spatially separated to opposite ends of the cell
22
Proximal
compartment
Distal
compartment
Microscopy image of the distal and proximal
compartments in S. aralocaspica
Nucleus
23. • Distal compartment
– Lack grana
– Pyruvate, Pi dikinase (PPDK) is present
– No starch
– C4 carbon fixation
• Proximal compartment
– Rubisco is concentrated
– NAD-malic enzyme is present
– C3 carbon fixation
23
Microscopy image of immunolocalization of
photosynthetic enzymes S.aralocaspica
Rubisco
PPDK
24. • In Bienertia Species
– One chloroplast type in the periphery [peripheral chloroplast (P-CP)]
– Other chloroplast type (central compartment chloroplast [C-CP]) in central
– Compartments are spatially separated by a vacuole
– Cytoplasmic compartments are interconnected by cytoplasmic channels
(Voznesenskaya et al., 2002; Edwards et al., 2004)
24
Peripheral compartment
Central compartment
Nucleus
Microscopy image of the peripheral and
central compartments in B. sinuspersici
Cell compartmentalization (2)
25. • Peripheral cytoplasmic compartment (PCC)
– Less number of mitochondria
– Has grana-deficient chloroplasts
– Contain pyruvate, Phosphate dikinase,
Phosphoenolpyruvate carboxylase
– C4 carbon fixation
• Central cytoplasmic compartment (CCC)
– Filled with mitochondria and granal chloroplasts
– Rubisco is abundant
– C3 carbon fixation
25
26. 26
The actin cytoskeleton in chlorenchyma cells of B. sinuspersici (left) and
S. aralocaspica (right)
Actin cytoskeleton
( Source: Chuong et al., 2006)
28. Aquatic single cell C4 photosynthesis
• CO2 HCO3
- in water
• The availability of inorganic carbon for photosynthesis in water
is limited by diffusion and pH.
• Some eukaryotic phytoplankton/ angiosperm species have
evolved energy dependent mechanisms for concentrating CO2.
1. Thalassiosira weissflogii
2. Hydrilla verticillata
28
29. Thalassiosira weissflogii
• Centric, unicellular diatom
• Found in marine environments and also in inland waters in
many parts of the world
• Initial incorporation of CO2 into four carbon acids and the
subsequent transfer of carbon to 3-phosphoglycerate and
sugars
Image of Thalassiosira weissflogii
29
30. Hydrilla verticillata
• Found in fresh water environments
• C4 photosynthesis is accomplished without any
compartmentation and chloroplast differentiation.
• A facultative C4 plant
30
A photograph of Hydrilla verticillata
31. Discussion
• Many important crops are C3 plants.
• The solar energy conversion efficiency to biomass is lower in C3
photosynthesis than that of C4 photosynthesis.
• C4 plants were evolved from C3 plants, acquiring the C4 photosynthetic
pathway in addition to the C3 pathway.
• Transfer of C4 traits to C3 plants has been one strategy for improving the
photosynthetic performance of C3 plants.
• This was initially attempted by means of conventional hybridization between
C3 and C4 plants and more recently using transgenic techniques.
– e.g. C4 rice project
31
32. • Akhani, H., Barroca, J., Koteeva, N., Voznesenskaya, E., Franceschi, V., Edwards, G., Ghaffari, M., and Ziegler, H.
(2005). Bienertia sinuspersici (Chenopodiaceae): a new species from Southwest Asia and discovery of a third
terrestrial C4 plant without Kranz anatomy. Systematic Botany 30(2): 290–301.
• Bowes, G., Rao, S.K., Estavillo, G.M., Reiskind, J.B. (2002). C4 mechanisms in aquatic angiosperms:
comparisons with terrestrial C4 systems. Functional Plant Biology 29: 379–392.
• Brown, R.H., Bouton, J.H. (1993). Physiology and genetics of inter specific hybrids between photosynthetic
types. Annual Review of Plant Physiology and Plant Molecular Biology 44: 435–456.
• Chuong, S.D.X., Franceschi, V.R., and Edwards, G.E. (2006). The cytoskeleton maintains organelle partitioning
required for single-cell C4 photosynthesis in Chenopodiaceae Species. The Plant Cell 18: 2207–2223.
• Edwards, G.E., Franceschi, V.R., Voznesenskaya, E.V. (2004). Single cell C4 photosynthesis versus the dual-cell
(Kranz) paradigm. Annual Review of Plant Biology 55, 173–196.
• Fukayama, H., Tsuchida, H., Agarie, S. (2001). Significant accumulation of C4-specific
pyruvate, orthophosphate dikinase in a C3 plant, rice. Plant Physiology 127, 1136–1146.
• Hatch, M.D. (1987). C4 photosynthesis: a unique blend of modified biochemistry, anatomy and ultrastructure.
Biochimica et Biophysica Acta 895, 81–106.
• Hausler, R.E., Hirsch, H.J., Peterhansel, K.F. (2002). Overexpression of C4-cycle enzymes in transgenic C3 plants:
a biotechnological approach to improve C3-photosynthesis. Journal of Experimental Botany 53, 591–607.32
References
33. • Lara, M.V., Chuong, S.D.X., Akhani, H., Andreo, C.S., and Edwards, G.E. (2006). Species having C4 single-cell-
type photosynthesis in the Chenopodiaceae family evolved a photosynthetic Phosphoenolpyruvate
carboxylase like that of Kranz-type C4 species. Plant Physiology 142: 673–684.
• Miyao, M., Masumoto, C., Miyazawa, S., and Fukayama, H. (2011). Lessons from engineering a single-cell
C4 photosynthetic pathway into rice. Journal of Experimental Botany 62(9): 3021–3029.
• Offermann, S., Okita, T.W., and Edwards, G.E. (2011). Resolving the Compartmentation and Function of C4
Photosynthesis in the Single-Cell C4 Species Bienertia sinuspersici. Plant Physiology 155: 1612–1628.
• Voznesenskaya, E.V., Edwards, G.E., Kiirats, O., Artyusheva, E.G., and Franceschi, V.R. (2003). Development
of biochemical specialization and organelle partitioning in the single celled C4 system in leaves of
Borszczowia aralocaspica (Chenopodiaceae). American Journal of Botany 90, 1669–1680.
• Voznesenskaya, E.V., Franceschi, V.R., and Edwards, G.E. (2004). Light-dependent development of single
cell C4 photosynthesis in cotyledons of Borszczowia aralocaspica (chenopodiaceae) during transformation
from a storage to a photosynthetic organ. Annals of Botany 93: 177-187.
• Voznesenskaya, E.V., Franceschi, V.R., Kiirats, O., Artyusheva, E.G., Freitag, H., and Edwards, G.E. (2002).
Proof of C4 photosynthesis without Kranz anatomy in Bienertia cycloptera (Chenopodiaceae). The Plant
Journal 31: 649–662.
• Voznesenskaya, E.V., Franceschi, V.R., Kiirats, O., Freitag, H., and Edwards, G.E. (2001). Kranz anatomy is not
essential for terrestrial C4 plant photosynthesis. Nature 414: 543–546
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