Kranz Anatomy and the C4 Pathway

Abstract

C4 photosynthesis incorporates novel leaf anatomy, metabolic specialisations and modified gene expression. C4 plants typically possess a distinctive Kranz leaf anatomy consisting of two photosynthetic cell types. These are bundle sheath (BS) cells that surround the vascular centres, and mesophyll (M) cells that, in turn, surround the BS cells. A more rare form uses compartmentalisation of dimorphic chloroplasts within a single cell type. In C4 leaves, these structural frameworks functionally separate two sets of carboxylation and decarboxylation reactions. Selective expression of key photosynthesis genes in BS and M cells leads to specific accumulation of key photosynthetic enzymes which catalyse different sets of cell‐type‐specific reactions, enabling these plants to assimilate atmospheric CO2 with very high efficiency. For some plants, C4 photosynthesis has facilitated their adaptation to arid conditions, high temperatures and marginal environments. Understanding the basis of this pathway has applications for improvements in agricultural productivity and alternative fuel development.

Key Concepts

  • C4 photosynthesis is a carbon concentration mechanism used by some plants to improve the efficiency of photosynthetic carbon fixation.
  • C4 photosynthesis incorporates modified leaf morphology, separation of carboxylation and decarboxylation/refixation steps of carbon assimilation, and specialised patterns of cell‐type‐specific gene expression.
  • The leaves of most C4 plants possess a Kranz‐type anatomy consisting of bundle sheath and mesophyll cells. A more rare form of this pathway, called single‐cell C4, uses partitioning of dimorphic chloroplasts to separate different sets of reactions within a single leaf cell type.
  • In C4 leaves, Rubisco is localised only within internalised bundle sheath cells, or internalised chloroplasts, to protect from atmospheric O2 and limit the oxygenase activity of this enzyme. The initial carbon assimilation enzyme in these leaves is PEPCase, which incorporates CO2 but not O2.
  • Reactions of C4 pathway work as a pump to concentrate CO2 in the vicinity of the internalised Rubisco enzyme. These reduce or eliminate photorespiration, thereby enhancing photosynthetic efficiency.
  • C4 plants are more efficient than C3 plants under arid conditions, including high temperatures and water stress. C4 plants show increased efficiency of water and nitrogen use, allowing them to outcompete C3 plants in marginal environments.
  • Bioengineering of C4 characteristics into C3 species has the potential to improve photosynthetic efficiency in crop plants used for food and biofuel.

Keywords: photosynthesis; carbon fixation; leaf anatomy; bundle sheath cells; mesophyll cells; photorespiration, evolution; environmental adaptability; cytology; C4 variations; C4 enzymes; gene regulation; biotechnology

Figure 1. Diagrammatic representation of Kranz anatomy and the C4 pathway. Panel (a) shows typical Kranz leaf anatomy with bundle sheath (BS) and mesophyll (M) cells within a leaf cross‐section. Panel (b) shows a simplified representation of the C4 pathway superimposed on an enlarged diagram of the two cell types, indicating the cellular localisation of carboxylation, decarboxylation and re‐assimilation reactions. V, vascular centre; BS, bundle sheath cells; M, mesophyll cells; E, upper or lower leaf epidermal cells, PEP, phosphoenolpyruvate carboxylase, RuBP, ribulose‐1,5‐bisphosphate.
Figure 2. Comparison of leaf anatomy and photosynthetic pathways in C3 (left panels) and Kranz‐type C4 (right panels) plants. Top left, Rubisco localisation in C3 leaf. Rubisco (observed as yellow‐coloured fluorescence) is located within the chloroplasts of all leaf photosynthetic cell types. Cells and structures that do not contain Rubisco are visualised by their blue autofluorescence. Top right, Rubisco localisation in Kranz‐type C4 leaf. Rubisco (observed as yellow‐coloured fluorescence) is localised within the chloroplasts of bundle sheath (BS) cells, and not in the chloroplasts of mesophyll cells (M, observed as blue autofluorescence). For the top two panels, Rubisco localisation in leaves of tobacco (C3) and maize (C4) was visualised using antisera specific for the large subunit (LSU) protein of Rubisco. For these images, leaf sections were reacted using the LSU antisera, and a secondary antibody conjugated with the fluorescent dye Alexafluor 546. This method, called immunolocalisation, identifies where Rubisco is localised as yellow fluorescence. Cells that do not contain Rubisco are visualised by blue autofluorescence. UE, upper epidermis; LE, lower epidermis, V, vascular centre; G, guard cells/stomate; M, mesophyll cell; B, bundle sheath cell, Rub, Rubisco, PPC, phosphoenol pyruvate carboxylase. These images were captured using the 40x objective of a Zeiss LSM710‐In Tune Lazer Scanning Confocal Microscope. The scale bar in these images = 100 μM. Bottom left. Diagrammatic representation of Rubisco activity in the leaf mesophyll cells of plants that use the C3 pathway of photosynthesis. A, Both CO2 and O2 from the atmosphere enter the leaf through stomata located at the leaf epidermis (E). B, Rubisco, located in all photosynthetic leaf mesophyll cells, binds to carbon dioxide (CO2, green arrow) or oxygen (O2, red arrow), C, Binding to CO2 leads to the production of 3 carbon 3‐phosphoglycerate (3‐PGA) for the Calvin–Benson cycle (green arrow), and the net assimilation of carbon into the biosphere. In the competing reaction of this enzyme, binding to O2 leads to the production of 2 carbon phosphoglycolate (PG), leading to metabolic wasteful pathway of photo respiration (red arrow), in which no carbon is assimilated by the plant. Bottom right, Diagrammatic representation of PEPCase and Rubisco activity. Both CO2 and O2 from the atmosphere enter the leaf through stomata located at the leaf epidermis (E). The CO2 binds to PEPCase, the initial CO2 fixation in C4 plants. PEPCase does not bind to O2. The C4 acid produced by PEPCase is transported to the BS cells, where it is decarboxylated to release CO2 for refixation by Rubisco. 1, PEPCase (PPC) in M cells binds to CO2; 2, the result of fixation by PEPCase is a C4 acid; 3, The C4 acid is transported into the BS cell; 4, The C4 acid is decarboxylated in BS cells, releasing CO2; 5, 3‐carbon phosphoenol pyruvate (PEP) is transported back into the M cells to serve as a substrate for PEPCase and CO2. Yellow diamonds, carbon; blue circles, oxygen; E, epidermis.
Figure 3. (a) Localisation of Rubisco to central compartment chloroplasts in leaf cells of ., a plant that uses a rare form of single cell C4 photosynthesis. CCC, central compartment chloroplasts; PCC, peripheral compartment chloroplasts. Note that Rubisco accumulates specifically within the internalised CCCs, observed as a sphere of chloroplasts. Little or no accumulation within the outermost PCCs of these cells. For the laser scanning confocal image, Rubisco is observed as a gold colour, while the rest of the cell is visualised by differential interfering contrast (DIC) imaging. Reaction of the Bienertia sections with primary and secondary antisera was performed as described for the panel (a) of Figure. Scale bar = 50 μM. (b) Diagrammatic representation of single‐cell C4 chlorenchyma cell anatomy and C4 pathway. The diagram shows the intracellular of different photosynthetic compartments within a SC‐C4 leaf chlorenchyma cell. The yellow/gold colour used to highlight the CCC represents the specific localisation of Rubisco and Calvin–Benson cycle enzymes within these internalised chloroplasts. A simplified representation of the C4 pathway superimposed on the diagram indicates where carboxylation, decarboxylation and re‐assimilation reactions occur within the cell. CC, central compartment, PC, peripheral compartment, CCC, central compartment chloroplasts, PCC, peripheral compartment chloroplasts, PEP, phosphoenolpyruvate carboxylase, RuBP, ribulose‐1,5‐bisphosphate.
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References

Ambrose SH and Krigbaum J (2003) Bone chemistry and bioarchaeology. Journal of Anthropological Archaeology 22: 193–199.

Aubry S, Smith‐Unna RD, Boursnell CM, Kopriva S and Hibberd JM (2014) Transcript residency on ribosomes reveals a key role for the Arabidopsis thaliana bundle sheath in sulphur and glucosinolate metabolism. Plant Journal 78: 659–673. DOI: 10.1111/tpj.12502.

Berry JO, Zielinski AM and Patel M (2011) Gene expression in mesophyll and bundle sheath cells of C4 plants. In: Raghavendra AS and Sage RF (eds) C4 Photosynthesis and Related CO2 Concentrating Mechanisms. Advances in Photosynthesis and Respiration, vol. 32, pp. 221–256. Dordrecht: Springer.

Berry JO, Yerramsetty P, Mure C and Zielinski AM (2013) Photosynthetic gene expression in higher plants. Photosynthesis Research 117: 91–120.

Bevan MW and Franssen MCR (2006) Investing in green and white biotech. Nature Biotechnology 24: 765–767.

Bhattacharjee S, Renganaath K, Mehrotra R and Mehrotra S (2013) Combinatorial control of gene expression. BioMed Research International 2013: 407263. DOI: 10.1155/2013/407263.

Bowman SM, Patel M, Yerramsetty P, et al. (2013) A novel RNA binding protein affects rbcL gene expression and is specific to bundle sheath chloroplasts in C4 plants. BMC Plant Biology 13: 138. DOI: 10.1186/1471-2229-13-138.

von Caemmerer S and Furbank RT (2003) The C4 pathway: an efficient C4 pump. Photosynthesis Research 77: 191–207.

Dengler NG and Nelson T (1999) Leaf structure and development in C4 plants. In: Sage RF and Monson RK (eds) C4 Plant Biology, pp. 133–172. San Diego, CA: Academic Press.

Edwards GE, Franceschi VR and Voznesenskaya EV (2004) Single cell C4 photosynthesis versus the dual‐cell (Kranz) paradigm. Annual Review of Plant Physiology and Plant Molecular Biology 55: 173–196.

Edwards GE and Voznesenskaya EV (2011) C4 photosynthesis: Kranz forms and single‐cell C4 in terrestrial plants. In: Raghavendra AS and Sage RF (eds) C4 Photosynthesis and Related CO2 Concentrating Mechanisms. Advances in Photosynthesis and Respiration, vol. 32, pp. 29–61. Dordrecht: Springer.

Ghannoum O, Evans J and von Caemmerer S (2011) Nitrogen and water use efficiency of C4 plants. In: Raghavendra AS and Sage RF (eds) C4 Photosynthesis and Related CO2 Concentrating Mechanisms. Advances in Photosynthesis and Respiration, vol. 32, pp. 129–146. Dordrecht: Springer.

Guerra D, Crosatti C, Khoshro HH, et al. (2015) Post‐transcriptional and post‐translational regulations of drought and heat response in plants: a spider's web of mechanisms. Frontiers in Plant Science 6: 57.

Hatch MD (1987) C4 photosynthesis: a unique blend of modified biochemistry, anatomy and ultrastructure. Biochimica et Biophysica Acta 895: 81–106.

Hatch MD (2005) C4 photosynthesis: discovery and resolution. In: Govindjee J, Beatty T, Gest H and Allen JF (eds) Discoveries in Photosynthesis. Advances in Photosynthesis and Respiration, vol. 20, pp. 875–880. Dordrecht: Springer.

Heckmann D, Schulze S, Denton A, et al. (2013) Predicting C4 photosynthesis evolution: modular, individually adaptive steps on a Mount Fuji fitness landscape. Cell 153: 1579–1588.

Hibberd JM and Covshoff S (2010) The regulation of gene expression required for C4 photosynthesis. Annual Review of Plant Biology 61: 181–207.

Jones MB (2011) C4 species as energy crops. In: Raghavendra AS and Sage RF (eds) C4 Photosynthesis and Related CO2 Concentrating Mechanisms. Advances in Photosynthesis and Respiration, vol. 32, pp. 379–397. Dordrecht: Springer.

Kani R and Edwards GE (1999) The biochemistry of C4 photosynthesis. In: Sage RF and Monson RK (eds) C4 Plant Biology, pp. 49–87. San Diego: Academic Press.

Koteyeva NK, Voznesenskaya EV, Berry JO, Cousins AB and Edwards GE (2016) The unique structural and biochemical development of single cell C4 photosynthesis along longitudinal leaf gradients in Bienertia sinuspersici and Suaeda aralocaspica (Chenopodiaceae). Journal of Experimental Botany (Advanced Access, published March 8, 2016). DOI: 10.1093/jxb/erw082.

Krigbaum J (2008) Stable isotope analysis. In: Pearsall DM (ed) Encyclopedia of Archaeology, pp. 2075–2077. Amsterdam: Elsevier.

Leegood RC (2007) Roles of bundle sheath cells in leaves of C3 plants. Journal of Experimental Botany 59: 1663–1673.

Maai E, Miyake H and Taniguchi M (2011) Differential positioning of chloroplasts in C4 mesophyll and bundle sheath cells. Plant Signaling & Behavior 6: 1111–1113.

Mallman J, Heckmann D, Bräutigam A, et al. (2014) The role of photorespiration during the evolution of C4 photosynthesis in the genus Flaveria. eLife. DOI: 10.7554/eLife.02478.

McKown AD and Dengler NG (2007) Key innovations in the evolution of Kranz anatomy and C4 vein pattern in Flaveria (Asteraceae). American Journal of Botany 94: 382–399.

Mommer L and Visser EJW (2005) Underwater photosynthesis in flooded terrestrial plants: a matter of leaf plasticity. Annals of Botany 96: 581–589.

Osborn CP and Freckleton RP (2009) Ecological selection pressures for C4 photosynthesis in the grasses. Proceedings of the Royal Society B‐Biological Sciences 276: 1754–1760.

Patel M and Berry JO (2008) Rubisco gene expression in C4 plants. Journal of Experimental Botany 59: 1625–1634.

Rosnow J, Yerramsetty P, Berry JO, Okita TW and Edwards GE (2014) Exploring mechanisms linked to differentiation and function of dimorphic chloroplasts in the single cell C4 species Bienertia sinuspersici. BMC Plant Biology 14: 34. DOI: 10.1186/1471-2229-14-34.

Sage RF (2003) The evolution of C4 photosynthesis. New Phytologist 161: 341–370.

Sage RF and Zhu XG (2011) Exploiting the engine of C4 photosynthesis. Journal of Experimental Botany 62: 2989–3000.

Sage RF, Sage TL and Kocacinar F (2012) Photorespiration and the evolution of C4 photosynthesis. Annual Review of Plant Physiology and Plant Molecular Biology 63: 19–47.

Sage TL, Busch FA, Johnson DC, et al. (2013) Initial events during the evolution of C4 photosynthesis in C3 species of Flaveria. Plant Physiology 163: 1266–1276.

Schulze S, Mallmann J, Burscheidt J, et al. (2013) Evolution of C4 photosynthesis in the genus Flaveria: establishment of a photorespiratory CO2 pump. Plant Cell 25: 2522–2535.

Tolbert NE, Benker C and Beck E (1995) The oxygen and carbon dioxide compensation points of C3 plants: possible role in regulating atmospheric oxygen. Proceedings of the National Academy of Sciences of the United States of America 92: 11230–11233.

Ueno O (2001) Environmental regulation of C3 and C4 differentiation in the amphibious sedge Eleocharis vivipara. Plant Physiology 127: 1524–1532.

Westhoff P and Gowik U (2010) Evolution of C4 photosynthesis‐looking for the master switch. Plant Physiology 154: 598–601.

Further Reading

Berry JO, Yerramsetty P, and Mure C (2016) Regulation of Rubisco gene expression in higher plants. Current Opinion in Plant Biology, 31: 23–28.

Govindjee J, Beatty T, Gest H and Allen JF (eds) (2005) Discoveries in Photosynthesis. Advances in Photosynthesis and Respiration, vol. 20. Dordrecht: Springer.

Long SP, Marshall‐Colon A and Zhu X‐G (2015) Meeting the global food demand of the future by engineering crop photosynthesis and yield potential. Cell 161: 56–66.

Martin DL, Harrod RP and Pérez VR (2013) Bioarchaeology: An Integrated Approach to Working with Human Remains. New York: Springer.

Ort DR, Merchant SS, Alric J, et al. (2015) Redesigning photosynthesis to sustainably meet global food and bioenergy demand. Proceedings of the National Academy of Sciences of the United States of America 112: 8529–8536.

Raghavendra AS and Sage RF (eds) (2011) C4 Photosynthesis and Related CO2 Concentrating Mechanisms. Advances in Photosynthesis and Respiration, vol. 32. Dordrecht: Springer.

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Garner, Drake MG, Mure, Christopher M, Yerramsetty, Pradeep, and Berry, James O(Jul 2016) Kranz Anatomy and the C4 Pathway. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1002/9780470015902.a0001295.pub3]