Metabolic networks of Cucurbita maxima phloem

Fiehn, Oliver

doi:10.1016/s0031-9422(02)00715-x

Cited by 149 publications

(113 citation statements)

References 52 publications

Supporting

Mentioning

104

Contrasting

Unclassified

Order By: Relevance

“…For EFP sap composition, we used phloem exudates. In previous reports (18,29), the metabolome of cucurbit phloem exudates was found to contain amino acids and secondary metabolites at concentrations similar to phloem of other plants. However, many of the amino acids and secondary metabolites present in phloem exudates are not detectable or are at trace levels in FP tissues (Fig.…”

Section: Differences In Metabolome Composition Between Two Phloemmentioning

confidence: 83%

See 1 more Smart Citation

Divergent metabolome and proteome suggest functional independence of dual phloem transport systems in cucurbits

Zhang

Tolstikov

Turnbull

et al. 2010

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

Self Cite

133

131

View full text Add to dashboard Cite

Cucurbitaceous plants (cucurbits) have long been preferred models for studying phloem physiology. However, these species are unusual in that they possess two different phloem systems, one within the main vascular bundles [fascicular phloem (FP)] and another peripheral to the vascular bundles and scattered through stem and petiole cortex tissues [extrafascicular phloem (EFP)]. We have revisited the assumption that the sap released after shoot incision originates from the FP, and also investigated the long-standing question of why the sugar content of this sap is ∼30-fold less than predicted for requirements of photosynthate delivery. Video microscopy and phloem labeling experiments unexpectedly reveal that FP very quickly becomes blocked upon cutting, whereas the extrafascicular phloem bleeds for extended periods. Thus, all cucurbit phloem sap studies to date have reported metabolite, protein, and RNA composition and transport in the relatively minor extrafascicular sieve tubes. Using tissue dissection and direct sampling of sieve tube contents, we show that FP in fact does contain up to 1 M sugars, in contrast to low-millimolar levels in the EFP. Moreover, major phloem proteins in sieve tubes of FP differ from those that predominate in the extrafascicular sap, and include several previously uncharacterized proteins with little or no homology to databases. The overall compositional differences of the two phloem systems strongly indicate functional isolation. On this basis, we propose that the fascicular phloem is largely responsible for sugar transport, whereas the extrafascicular phloem may function in signaling, defense, and transport of other metabolites.cucurbitaceae | symplastic loading | extrafascicular | exudate | P-protein

show abstract

Section: Differences In Metabolome Composition Between Two Phloemmentioning

confidence: 83%

“…Many explanations have been advanced. One suggestion is that the low RFO concentration in exudates is due to dilution by surrounding cells or by xylem sap (17), but this can be discounted based on the magnitude of dilution required, and from the fact that amino acid levels are similar to other species (18). These controversies have recently been reviewed (19).…”

mentioning

confidence: 99%

Divergent metabolome and proteome suggest functional independence of dual phloem transport systems in cucurbits

Zhang

Tolstikov

Turnbull

et al. 2010

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

Self Cite

133

131

View full text Add to dashboard Cite

show abstract

“…In addition, expression was induced in older leaves, mainly along the midvein and also in wounded leaves and inflorescence stems. The expression pattern and substrate specificity of AtPLT5 indicate that it may play a role in providing sink tissues with a range of carbohydrates known to be present in the phloem (29) and assumed to be transported into sink cells.…”

Section: Discussionmentioning

confidence: 99%

Analysis of Transport Activity of Arabidopsis Sugar Alcohol Permease Homolog AtPLT5

Reinders

Panshyshyn

Ward

2005

Journal of Biological Chemistry

View full text Add to dashboard Cite

The transporters responsible for sugar uptake into non-photosynthetic sink tissues in plants, such as roots and flowers, have not been fully identified and analyzed. Plants encode around 100 putative sugar transporters within the major facilitator superfamily, yet only a few have been studied. Here we report the analysis of a sugar alcohol permease homolog (AtPLT5, At3g18830) from Arabidopsis. A wide range of sugars including hexoses, pentoses, tetroses, a sugar acid, and sugar alcohols but not disaccharides induced inward currents in oocytes expressing AtPLT5. AtPLT5 expression also resulted in 14 C-labeled substrate uptake in oocytes, indicating that AtPLT5 encodes an ion-coupled uptake transporter. K 0.5 values for glucose and sorbitol were highly dependent on external pH. Expression of AtPLT5 was found primarily in sink tissues: in the elongation zone of roots, in the inflorescence stem, and several floral structures, especially in the floral abscission zone. Expression was induced by mechanical wounding and insect feeding. Analysis of transport properties and expression in Arabidopsis indicate that AtPLT5 functions to transport a wide range of sugars into specific sink tissues in the plant.Most plant cells are connected by plasmodesmata, forming multicellular "symplasmic domains" (1) that allow exchange of small metabolites between cells. Transporters in the plasma membrane are required for transmembrane metabolite uptake into specific cell types, such as guard cells, pollen cells, and the sieve element/companion cell (SE/CC) complex that are symplasmically isolated. In addition, symplasmic domains of sink cells, for example, in fruit (2), require metabolite uptake transporters to support growth and development (for review, see Ref.3). Furthermore, events such as wounding, dehiscence, or programmed cell death will release metabolites into the cell wall space, and it is expected that surrounding cells have the capability to take up the released compounds.Although not yet functionally characterized, specific sugar transporter homologs are expressed during senescence (4), dehydration (5, 6), or pathogen attack (7) and may function in metabolite uptake. Arabidopsis encodes a wide array of metabolite transporters, around 100 potential metabolite transporters within the major facilitator superfamily (MFS) 1 alone. Available sequence data indicates that a similar situation exists in other plant species as well. Aside from the well characterized STP family of hexose transporters (8), very little information is available concerning transport activity of plant MFS members.Within the MFS, Arabidopsis encodes three groups of transporters that are closely related to the inositol permeases ITR1 and ITR2 from Schizosaccharomyces pombe (9) and Saccharomyces cerevisiae (10) and the xylose permease from Lactobacillus brevis (11). One group of four genes contains AtpGlcT (At5g16150), the plastidic glucose translocator (12). A second group of four genes is most similar to the plant vacuolar inositol permeases (Mitr1 and Mitr2)...

show abstract

“…However, because most metabolites are present to some degree in virtually all tissues and fluids, it is only a difference in concentration of metabolites that distinguishes key biologically important differences in phenotype/outcome. Therefore, it is vital that metabolite data be quantitative to be suitable for producing databases that provide unbiased biological information about a sample, and that can be used to compare different samples, phenotypes or outcomes, to fit metabolic models and to assess the integrated flux through all metabolic pathways (Watkins et al, 2002;Fiehn, 2003). Such data can continue to be compared, mined and fitted to pursue various hypotheses, including those that are unrelated to the basic hypothesis that was used to produce the data in the first place.…”

Section: Data Requirements For Metabolomic Databasesmentioning

confidence: 99%

Metabolomics: building on a century of biochemistry to guide human health

German

Hammock

Watkins³

2005

Metabolomics

295

197

View full text Add to dashboard Cite

Medical diagnosis and treatment efficacy will improve significantly when a more personalized system for health assessment is implemented. This system will require diagnostics that provide sufficiently detailed information about the metabolic status of individuals such that assay results will be able to guide food, drug and lifestyle choices to maintain or improve distinct aspects of health without compromising others. Achieving this goal will use the new science of metabolomicscomprehensive metabolic profiling of individuals linked to the biological understanding of human integrative metabolism. Candidate technologies to accomplish this goal are largely available, yet they have not been brought into practice for this purpose. Metabolomic technologies must be sufficiently rapid, accurate and affordable to be routinely accessible to both healthy and acutely ill individuals. The use of metabolomic data to predict the health trajectories of individuals will require bioinformatic tools and quantitative reference databases. These databases containing metabolite profiles from the population must be built, stored and indexed according to metabolic and health status. Building and annotating these databases with the knowledge to predict how a specific metabolic pattern from an individual can be adjusted with diet, drugs and lifestyle to improve health represents a logical application of the biochemistry knowledge that the life sciences have produced over the past 100 years.

show abstract

Metabolic networks of Cucurbita maxima phloem

Cited by 149 publications

References 52 publications

Divergent metabolome and proteome suggest functional independence of dual phloem transport systems in cucurbits

Divergent metabolome and proteome suggest functional independence of dual phloem transport systems in cucurbits

Analysis of Transport Activity of Arabidopsis Sugar Alcohol Permease Homolog AtPLT5

Metabolomics: building on a century of biochemistry to guide human health

Contact Info

Product

Resources

About