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Phloem pp 223-233 | Cite as

Assessing Long-Distance Carbon Partitioning from Photosynthetic Source Leaves to Heterotrophic Sink Organs with Photoassimilated [14C]CO2

  • Umesh P. Yadav
  • Mearaj A. Shaikh
  • John Evers
  • Kamesh C. Regmi
  • Roberto A. Gaxiola
  • Brian G. AyreEmail author
Protocol
Part of the Methods in Molecular Biology book series (MIMB, volume 2014)

Abstract

Phloem loading and long-distance transport of photoassimilate from source leaves to sink organs are essential physiological processes that contribute to plant growth and yield. At a minimum, three steps are involved: phloem loading in source organs, transport along the phloem path, and phloem unloading in sink organs. Each of these can have variable rates contingent on the physiological state of the plant, and thereby influence the overall transport rate. In addition to these phloem transport steps, rates of photosynthesis and photosynthate movement in the pre-phloem path, as well as photosynthate utilization in post phloem tissues of sink organs also contribute to phloem transport. The protocol described here estimates carbon allocation along the entire path from initial carbon fixation to delivery to sink organs after a labeling pulse: [14C]CO2 is photoassimilated in source leaves and loading and transport of the 14C label to heterotrophic sink organs (roots) is quantified by scintillation counting. This method is flexible and can be adapted to quantify long-distance transport in many plant species.

Key words

Photosynthetic labeling 14C labeling Phloem transport Photoassimilate partitioning Source-sink relations Carbon allocation Sugar transport 

Notes

Acknowledgments

Work on phloem loading and long-distance transport in B.G. Ayre’s laboratory is/was supported by the National Science Foundation grants 0344088, 0922546, 1121819, and 1558012. The authors thank Dr. Robert Turgeon for helpful discussion.

References

  1. 1.
    van Bel AJE (1996) Interaction between sieve element and companion cell and the consequences for photoassimilate distribution. Two structural hardware frames with associated physiological software packages in dicotyledons. J Exp Bot 47:1129–1140.  https://doi.org/10.1093/jxb/47.Special_Issue.1129CrossRefPubMedGoogle Scholar
  2. 2.
    Ayre BG (2011) Membrane-transport systems for sucrose in relation to whole-plant carbon partitioning. Mol Plant 4(3):377–394.  https://doi.org/10.1093/mp/ssr014CrossRefPubMedGoogle Scholar
  3. 3.
    Kempers R, Ammerlaan A, van Bel AJE (1998) Symplasmic constriction and ultrastructural features of the sieve element companion cell complex in the transport phloem of apoplasmically and symplasmically phloem-loading species. Plant Physiol 116(1):271–278.  https://doi.org/10.1104/pp.116.1.271CrossRefGoogle Scholar
  4. 4.
    Ruan Y-L, Llewellyn DJ, Furbank RT (2001) The control of single-celled cotton fiber elongation by developmentally reversible gating of plasmodesmata and coordinated expression of sucrose and K+ transporters and expansin. Plant Cell 13(1):47–60.  https://doi.org/10.1105/tpc.13.1.47PubMedPubMedCentralGoogle Scholar
  5. 5.
    Stadler R, Lauterbach C, Sauer N (2005) Cell-to-cell movement of green fluorescent protein reveals post-phloem transport in the outer integument and identifies symplastic domains in Arabidopsis seeds and embryos. Plant Physiol 139(2):701–712.  https://doi.org/10.1104/pp.105.065607CrossRefGoogle Scholar
  6. 6.
    Stadler R, Wright KM, Lauterbach C, Amon G, Gahrtz M, Feuerstein A, Oparka KJ, Sauer N (2005) Expression of GFP-fusions in Arabidopsis companion cells reveals non-specific protein trafficking into sieve elements and identifies a novel post-phloem domain in roots. Plant J 41(2):319–331.  https://doi.org/10.1111/j.1365-313X.2004.02298.xCrossRefGoogle Scholar
  7. 7.
    Yadav UP, Khadilkar AS, Shaikh MA, Turgeon R, Ayre BG (2017) Quantifying phloem loading in leaf disks with [14C]-sucrose. Bio Protocols 7(24):e2658.  https://doi.org/10.21769/BioProtoc.2658CrossRefGoogle Scholar
  8. 8.
    Yadav UP, Khadilkar AS, Shaikh MA, Turgeon R, Ayre BG (2017) Assessing rates of long-distance carbon transport in the phloem of Arabidopsis by collecting phloem exudations into EDTA solutions after photosynthetic labeling with [14C]CO2. Bio Protocols 7(24):e2656.  https://doi.org/10.21769/BioProtoc.2656CrossRefGoogle Scholar
  9. 9.
    Cao T, Lahiri I, Singh V, Louis J, Shah J, Ayre BG (2013) Metabolic engineering of raffinose-family oligosaccharides in the phloem reveals alterations in carbon partitioning and enhances resistance to green peach aphid. Front Plant Sci 4:263.  https://doi.org/10.3389/fpls.2013.00263CrossRefPubMedPubMedCentralGoogle Scholar
  10. 10.
    Dasgupta K, Khadilkar AS, Sulpice R, Pant B, Scheible W-R, Fisahn J, Stitt M, Ayre BG (2014) Expression of sucrose transporter cDNAs specifically in companion cells enhances phloem loading and long-distance transport of sucrose but leads to an inhibition of growth and the perception of a phosphate limitation. Plant Physiol 165(2):715–731.  https://doi.org/10.1104/pp.114.238410CrossRefPubMedPubMedCentralGoogle Scholar
  11. 11.
    Khadilkar AS, Yadav UP, Salazar C, Shulaev V, Paez-Valencia J, Pizzio GA, Gaxiola RA, Ayre BG (2016) Constitutive and companion cell-specific overexpression of AVP1, encoding a proton-pumping pyrophosphatase, enhances biomass accumulation, phloem loading, and long-distance transport. Plant Physiol 170(1):401–414.  https://doi.org/10.1104/pp.15.01409CrossRefPubMedGoogle Scholar
  12. 12.
    Yadav UP, Khadilkar AS, Shaikh MA, Turgeon R, Ayre BG (2017) Assessing long-distance transport from photosynthetic source leaves to heterotrophic sink organs with [14C]CO2. Bio Protocols 7(24):e2657.  https://doi.org/10.21769/BioProtoc.2657CrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media, LLC, part of Springer Nature 2019

Authors and Affiliations

  • Umesh P. Yadav
    • 1
  • Mearaj A. Shaikh
    • 1
  • John Evers
    • 1
  • Kamesh C. Regmi
    • 1
  • Roberto A. Gaxiola
    • 1
  • Brian G. Ayre
    • 1
    Email author
  1. 1.BioDiscovery Institute and Department of Biological SciencesUniversity of North TexasDentonUSA

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