Send to:

Choose Destination
See comment in PubMed Commons below
Plant Physiol. 1992 Nov;100(3):1433-41.

Turnover of soluble proteins in the wheat sieve tube.

Author information

  • 1Department of Botany, Washington State University, Pullman, Washington 99164-4238.


Although the enucleate conducting cells of the phloem are incapable of protein synthesis, phloem exudates characteristically contain low concentrations of soluble proteins. The role of these proteins and their movement into and out of the sieve tubes poses important questions for phloem physiology and for cell-to-cell protein movement via plasmodesmata. The occurrence of protein turnover in sieve tubes was investigated by [(35)S]methionine labeling and by the use of aphid stylets to sample the sieve tube contents at three points along a source-to-sink pathway (flag leaf to grains) in wheat plants (Triticum aestivum L.). Protein concentration and composition were similar at all sampling sites. The kinetics of (35)S-labeling of protein suggested a basically source-to-sink pattern of movement for many proteins. However, an appreciable amount of protein synthesis and, presumably, removal also occurred along the path. This movement appeared to be protein specific and not based on passive molecular sieving. The results have important implications for the transport capacities of plasmodesmata between sieve tubes and companion cells. The observations considerably expand the possible basis for ongoing sieve tube-companion cell interactions and, perhaps, interaction between sources and sinks.

Free PMC Article
PubMed Commons home

PubMed Commons

How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for HighWire Icon for PubMed Central
    Loading ...
    Write to the Help Desk