title: Determining protein identity from sieve element sap in Ricinus communis L. by quadrupole time of flight (Q-TOF) mass spectrometry.
abstract: The phloem transport system is a complex tissue that primarily carries photoassimilate from source to sink. Its function depends on anucleate sieve elements (SE) supported by companion cells (CC). In this study, SE sap was sampled and the protein identity of soluble proteins was determined with the aim of understanding the function of proteins within the conduit. Unlike many plants, SE sap exudes from incisions in the bark of Ricinus communis and, although there is a greater possibility of contamination from tissues other than SE, sap can be obtained in sufficient quantities to separate proteins using 2D electrophoresis. Spots were excised for trypsin digest, then analysed by quadrupole time of flight (Q-TOF) mass spectrometry (MS) and database searched to determine sequence identity. Overall, 18 proteins were identified in the SE-enriched sap. Proteins identified that have not previously been identified directly from SE sap included a glycine-rich RNA-binding protein, metallothionein, phosphoglycerate mutase, and phosphopyruvate hydratase. The potential role of the identified protein in SE function is discussed. The protein identification in this study provides a first step towards the goal of a greater understanding of the function of proteins within the SE.
authors.affiliation: The University of Birmingham, School of Biosciences, Edgbaston, Birmingham B15 2TT, UK.
authors.forename: Alan
authors.initials: A
authors.lastname: Barnes
authors.forename: Jeffery
authors.initials: J
authors.lastname: Bale
authors.forename: Chrystala
authors.initials: C
authors.lastname: Constantinidou
authors.forename: Peter
authors.initials: P
authors.lastname: Ashton
authors.forename: Anthony
authors.initials: A
authors.lastname: Jones
authors.forename: Jeremy
authors.initials: J
authors.lastname: Pritchard
mesh_terms: D000595:Amino Acid Sequence; D002367:Ricinus communis / Q000235:genetics*; D015180:Electrophoresis, Gel, Two-Dimensional; D013058:Mass Spectrometry / Q000379:methods; D018832:Molecular Chaperones / Q000235:genetics; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000302:isolation & purification; D012639:Seeds / Q000235:genetics; D014357:Trypsin
chemical_list: D018832:Molecular Chaperones; D010446:Peptide Fragments; D010940:Plant Proteins; D014357:Trypsin