Planta

, Volume 191, Issue 2, pp 207–213

Specific proteins in the sieve-tube exudate of Ricinus commuais L. seedlings: separation, characterization and in-vivo labelling

  • Thomas Sakuth
  • Christian Schobert
  • Attila Pecsvaradi
  • Arnulf Eichholz
  • Ewald Komor
  • Gabriele Orlich
Article

DOI: 10.1007/BF00199751

Cite this article as:
Sakuth, T., Schobert, C., Pecsvaradi, A. et al. Planta (1993) 191: 207. doi:10.1007/BF00199751

Abstract

Ricinus communis L. seedlings exuded pure phloem sap from the cut hypocotyl for several hours. Throughout the entire exudation period proteins were present in the phloem exudate at a constant concentration ranging from 0.11 to 0.41 mg·ml−1 depending on the culture conditions and the age of the seedlings. Manipulation of the nutrient supply at the cotyledons after removal of the endosperm did not change the protein concentration in the exudate. Comparison of sieve-tube exudate proteins (STEPs) with soluble proteins extracted from the hypocotyl and the cotyledons showed a unique abundance of small proteins in the exudate, with molecular weights ranging from 10 to 25 kDa. Bands at 18, 19 and 20 kDa were especially dominant. The proteins found transiently in the xylem exudate, which might represent proteins secreted at the wound surface, were different in pattern. Two-dimensional separation of STEPs revealed that more than 100 distinct polypeptides occurred in the sieve-tube exudate, most of them slightly acidic with isoelectric points ranging from 4 to 6 and a few basic ones around 8. [35S]Methionine fed to the cotyledons led to labelling of STEPs, demonstrating their rapid synthesis. It is concluded that there is a continuous synthesis and translocation of specific sieve-tube proteins, whose function is unknown.

Key words

EuphorbiaceaePhloem proteinRicinus[35S]Methionine labellingSieve tube exudateXylem exudate

Abbreviations

IEF

isoelectric focussing

pI

isoelectric point

STEP

sieve-tube exudate protein

SDS-PAGE

sodium dodecyl sulfate-polyacrylamide gel electrophoresis

TCA

trichloroacetic acid

Copyright information

© Springer-Verlag 1993

Authors and Affiliations

  • Thomas Sakuth
    • 1
  • Christian Schobert
    • 1
  • Attila Pecsvaradi
    • 1
  • Arnulf Eichholz
    • 1
  • Ewald Komor
    • 1
  • Gabriele Orlich
    • 1
  1. 1.Pflanzenphysiologie, Universität BayreuthBayreuthGermany
  2. 2.Department of Plant PhysiologyAttila Jozsef UniversitySzegedHungary