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Soluble and filamentous proteins in Arabidopsis sieve elements
Author(s) -
BATAILLER BRIGITTE,
LEMAÎTRE THOMAS,
VILAINE FRANÇOISE,
SANCHEZ CHRISTIAN,
RENARD DENIS,
CAYLA THIBAUD,
BENETEAU JULIE,
DINANT SYLVIE
Publication year - 2012
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.2012.02487.x
Subject(s) - phloem , sieve tube element , arabidopsis , biochemistry , exudate , arabidopsis thaliana , organelle , biology , chemistry , biophysics , botany , gene , mutant
Phloem sieve elements are highly differentiated cells involved in the long‐distance transport of photoassimilates. These cells contain both aggregated phloem‐proteins (P‐proteins) and soluble proteins, which are also translocated by mass flow. We used liquid chromatography–tandem mass spectrometry (LC‐MS/MS) to carry out a proteomic survey of the phloem exudate of Arabidopsis thaliana , collected by the ethylenediaminetetraacetic acid (EDTA)‐facilitated method. We identified 287 proteins, a large proportion of which were enzymes involved in the metabolic precursor generation and amino acid synthesis, suggesting that sieve tubes display high levels of metabolic activity. RNA‐binding proteins, defence proteins and lectins were also found. No putative P‐proteins were detected in the EDTA‐exudate fraction, indicating a lack of long‐distance translocation of such proteins in Arabidopsis . In parallel, we investigated the organization of P‐proteins, by high‐resolution transmission electron microscopy, and the localization of the phloem lectin PP2, a putative P‐protein component, by immunolocalization with antibodies against PP2‐A1. Transmission electron microscopy observations of P‐proteins revealed bundles of filaments resembling strings of beads. PP2‐A1 was found weakly associated with these structures in the sieve elements and bound to plastids. These observations suggest that PP2‐A1 is anchored to P‐proteins and organelles rather than being a structural component of P‐proteins.