Proteins and Fine Structural Components in Exudate from Sieve Tubes in Cucurbits pepo Stems

Walker, Travis S.; Thaine, R.

doi:10.1093/oxfordjournals.aob.a084523

Cited by 54 publications

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“…Given its scarcity in sugar-transporting fascicular phloem and its abundance in extrafascicular phloem, PP1 is unlikely to belong to this group of conventional P-proteins. However, Cucurbita exudates, predominantly comprising the contents of the extrafascicular phloem, have a strong tendency to gel (54,55), and this property may be attributable to PP1 (18). Therefore PP1-based gelling could represent an alternative wound-sealing mechanism to sieve plate occlusion by SEO proteins deployed in fascicular sieve tubes.…”

Section: Distribution Of Seo Genes Reveals the Uniformity Of P-proteinsmentioning

confidence: 99%

Sieve element occlusion(SEO) genes encode structural phloem proteins involved in wound sealing of the phloem

Ernst

Jekat

Zielonka

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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The sieve element occlusion (SEO) gene family originally was delimited to genes encoding structural components of forisomes, which are specialized crystalloid phloem proteins found solely in the Fabaceae. More recently, SEO genes discovered in various nonFabaceae plants were proposed to encode the common phloem proteins (P-proteins) that plug sieve plates after wounding. We carried out a comprehensive characterization of two tobacco (Nicotiana tabacum) SEO genes (NtSEO). Reporter genes controlled by the NtSEO promoters were expressed specifically in immature sieve elements, and GFP-SEO fusion proteins formed parietal agglomerates in intact sieve elements as well as sieve plate plugs after wounding. NtSEO proteins with and without fluorescent protein tags formed agglomerates similar in structure to native Pprotein bodies when transiently coexpressed in Nicotiana benthamiana, and the analysis of these protein complexes by electron microscopy revealed ultrastructural features resembling those of native P-proteins. NtSEO-RNA interference lines were essentially devoid of P-protein structures and lost photoassimilates more rapidly after injury than control plants, thus confirming the role of P-proteins in sieve tube sealing. We therefore provide direct evidence that SEO genes in tobacco encode P-protein subunits that affect translocation. We also found that peptides recently identified in fascicular phloem P-protein plugs from squash (Cucurbita maxima) represent cucurbit members of the SEO family. Our results therefore suggest a common evolutionary origin for P-proteins found in the sieve elements of all dicotyledonous plants and demonstrate the exceptional status of extrafascicular P-proteins in cucurbits.photoassimilate transport | wound response | exudation | phloem protein 1

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Section: Distribution Of Seo Genes Reveals the Uniformity Of P-proteinsmentioning

confidence: 99%

Sieve element occlusion(SEO) genes encode structural phloem proteins involved in wound sealing of the phloem

Ernst

Jekat

Zielonka

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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“…Protein filaments known as P-protein are the major structures microscopically observable in the sieve-tube lumen, but their function and positioning are disputed [2-41. Both the stream of translocates and the P-proteins are contained in a fluid exudate collected from mature sieve-tubes of certain plant species [5 -81.Phloem exudate from Cucurbita (pumpkin) forms a gel on exposure to air due to cross-linking of the filaments, and this can be prevented or reversed by agents which reduce disulphide bridges [9,10]. Reduction gives two proteins: phloem protein 1 (PPl), which reconstitutes filaments on oxidation [lo-121, and phloem protein 2 (PP2), which also precipitates on oxidation but does not form filaments [12], and which is a lectin specific for oligomers of N-acetylglucosamine [13 -151.…”

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confidence: 99%

“…Phloem exudate from Cucurbita (pumpkin) forms a gel on exposure to air due to cross-linking of the filaments, and this can be prevented or reversed by agents which reduce disulphide bridges [9,10]. Reduction gives two proteins: phloem protein 1 (PPl), which reconstitutes filaments on oxidation [lo-121, and phloem protein 2 (PP2), which also precipitates on oxidation but does not form filaments [12], and which is a lectin specific for oligomers of N-acetylglucosamine [13 -151.…”

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confidence: 99%

Subunit Structure and Interactions of the Phloem Proteins of Cucurbita maxima (Pumpkin)

Read

Northcote

1983

European Journal of Biochemistry

131

120

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1. The two major proteins from the phloem exudate of Cucurbita maxima (pumpkin), PP1 and PP2, were stable in the absence of reducing agents after modification of their accessible cysteine residues with iodoacetamide. This permitted their purification without precautions to prevent oxidation.2. PP2, a lectin specific for oligomers of N-acetyl-D-glucosamine, was shown by sedimentation-equilibrium ultracentrifugation to be a dimer of M, of 48000. Neither dithiothreitol nor tri-(N-acetyl-D-glucosamine) altered this value. The constituent polypeptides were linked by two buried disulphide bridges. PP2 behaved aberrantly on gel-filtration on both Sephadex and Bio-Gel unless tri-(N-acetyl-D-glucosamine) was added to the elution buffer; the M , was then measured as 46000. Other proteins which bind oligomers of N-acetyl-D-glucosamine are also retarded on gel-filtration.3. Soluble phloem filaments were prepared by collection of exudate into deaerated buffer containing iodoacetamide but no reducing agent. Oxidative gellation of the filaments was prevented by rapid modification of their many accessible cysteine residues, and is assumed to have maintained the degree of polymerisation found in vivo.Those disulphide bridges which were present allowed the incorporation of approximatically 60 % of the PP1 and 80 % of the PP2 into polymeric material. It is concluded that PP1 and PP2 are both structural proteins present in the filaments observable in vivo.4. PP2 had an elongated binding-site for oligomers of N-acetyl-D-glucosamine. It is suggested that this lectin immobilises bacteria and fungi to the cross-linked filaments which seal wounded phloem sieve-tubes, and thus maintains sterility.The sieve-tube cells of phloem tissue conduct organic nutrients around plants by intracellular mass-flow of the translocated material [l]. Protein filaments known as P-protein are the major structures microscopically observable in the sieve-tube lumen, but their function and positioning are disputed [2-41. Both the stream of translocates and the P-proteins are contained in a fluid exudate collected from mature sieve-tubes of certain plant species [5 -81.Phloem exudate from Cucurbita (pumpkin) forms a gel on exposure to air due to cross-linking of the filaments, and this can be prevented or reversed by agents which reduce disulphide bridges [9,10]. Reduction gives two proteins: phloem protein 1 (PPl), which reconstitutes filaments on oxidation [lo-121, and phloem protein 2 (PP2), which also precipitates on oxidation but does not form filaments [12], and which is a lectin specific for oligomers of N-acetylglucosamine [13 -151. Several different M , measurements have been given for these proteins: 88000-136000 for PP1 [4,10, 11,161 and 20000-60000 for PP2 [4,11,14,16].We show here that PP2 is a dimer of M , of 48000 held together by buried disulphide bridges, and that filaments from Cucurbita phloem contain both PP1 and PP2, which are therefore both structural proteins.Abbreviations. (GlcNAc),, (GlcNAc), and (Glc NAc),, di-, tri-, tetra-~-(1+4)-(2...

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“…Agar blocks have been employed to collect hormone exudates of decapitated seedlings (19) (7) and reducing agents (25) to enhance exudation. However, application of such techniques to seedling plants and plant epicotyls caused tissue damage, as evidenced by translucency and loss of ability to regenerate a shoot.…”

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A Technique for Collection of Exudate from Pea Seedlings

Hanson

Cohen

1985

Plant Physiol.

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Ethylenediaminetetraacetic acid (EDTA), at concentrations higher than 1.0 millimolar, is phytotoxic to etiolated seedlings of Pisum sativum. Substantial vascular exudation from pea epicotyls could be obtained without tissue damage at 0.5 millimolar EDTA if the solution was buffered at pH 7.5 with sodium N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid. Treated seedlings exuded 950 micrograms (leucine equivalents) of

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Proteins and Fine Structural Components in Exudate from Sieve Tubes in Cucurbits pepo Stems

Cited by 54 publications

References 0 publications

Sieve element occlusion(SEO) genes encode structural phloem proteins involved in wound sealing of the phloem

Sieve element occlusion(SEO) genes encode structural phloem proteins involved in wound sealing of the phloem

Subunit Structure and Interactions of the Phloem Proteins of Cucurbita maxima (Pumpkin)

A Technique for Collection of Exudate from Pea Seedlings

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