Osmoregulation and the control of phloem-sap composition in Ricinus communis L.

Smith, J. Andrew C.; Milburn, John A.

doi:10.1007/bf00385438

Cited by 87 publications

(58 citation statements)

References 25 publications

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“…Phloem exudate contained high concentrations of Suc with the values similar to those reported before (Hall and Baker, 1972;Smith and Milburn, 1980), while reducing sugars were absent (Fru) or present at only trace levels (Glc; Table I). Xylem exudate contained very small concentrations of Suc, Fru, and Glc.…”

Section: Sugar Composition In Phloem and Xylem Exudates Of Castor Beansupporting

confidence: 84%

Arsenic Speciation in Phloem and Xylem Exudates of Castor Bean

et al. 2010

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How arsenic (As) is transported in phloem remains unknown. To help answer this question, we quantified the chemical species of As in phloem and xylem exudates of castor bean (Ricinus communis) exposed to arsenate [As(V)], arsenite [As(III)], monomethylarsonic acid [MMA(V)], or dimethylarsinic acid. In the As(V)-and As(III)-exposed plants, As(V) was the main species in xylem exudate (55%-83%) whereas As(III) predominated in phloem exudate (70%-94%). The ratio of As concentrations in phloem to xylem exudate varied from 0.7 to 3.9. Analyses of phloem exudate using high-resolution inductively coupled plasma-mass spectrometry and accurate mass electrospray mass spectrometry coupled to high-performance liquid chromatography identified high concentrations of reduced and oxidized glutathione and some oxidized phytochelatin, but no As(III)-thiol complexes. It is thought that As(III)-thiol complexes would not be stable in the alkaline conditions of phloem sap. Small concentrations of oxidized glutathione and oxidized phytochelatin were found in xylem exudate, where there was also no evidence of As(III)-thiol complexes. MMA(V) was partially reduced to MMA(III) in roots, but only MMA(V) was found in xylem and phloem exudate. Despite the smallest uptake among the four As species supplied to plants, dimethylarsinic acid was most efficiently transported in both xylem and phloem, and its phloem concentration was 3.2 times that in xylem. Our results show that free inorganic As, mainly As(III), was transported in the phloem of castor bean exposed to either As(V) or As(III), and that methylated As species were more mobile than inorganic As in the phloem.Arsenic (As) is an environmental and food chain contaminant that has attracted much attention in recent years. Soil contamination with As may lead to phytotoxicity and reduced crop yield (Panaullah et al., 2009). Food crops are also an important source of inorganic As, a class-one carcinogen, in human dietary intake, and there is a need to decrease the exposure to this toxin (European Food Safety Authority, 2009). Paddy rice (Oryza sativa) is particularly efficient in As accumulation, which poses a potential risk to the population based on a rice diet Zhao et al., 2010a). Other terrestrial food crops generally do not accumulate as much As as paddy rice; however, where soils are contaminated, relatively high concentrations of As in wheat (Triticum aestivum) grain have been reported Zhao et al., 2010b). On the other hand, some fern species in the Pteridaceae family are able to tolerate and hyperaccumulate As in the aboveground part to .1,000 mg kg 21 dry weight (e.g. Ma et al., 2001;Zhao et al., 2002); these plants offer the possibility for remediation of Ascontaminated soil or water (Salido et al., 2003;Huang et al., 2004). A better understanding of As uptake and long-distance transport, metabolism, and detoxification is needed for developing strategies for mitigating As contamination, through either decreased As accumulation in food crops or enhanced As accumulation for phytoremedi...

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Section: Sugar Composition In Phloem and Xylem Exudates Of Castor Beansupporting

confidence: 84%

Arsenic Speciation in Phloem and Xylem Exudates of Castor Bean

et al. 2010

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“…Sap composition is known to be affected by the diurnal cycle; for example, in Ricinus communis, there was a diurnal reciprocity between phloem potassium and Suc concentrations (Smith and Milburn, 1980). Amino acids are loaded and unloaded into the ST through transporters, some localized to the vascular tissue (Rentsch et al, 2007).…”

Section: Discussionmentioning

confidence: 99%

“…Sap exchange between adjacent STs in a vascular bundle, however, is possible, as lateral sieve areas have been observed in angiosperms (Esau and Cheadle, 1959;Evert et al, 1966;Walsh and Melaragno, 1976), and osmolytes can also be exchanged between SEs by unloading and subsequent reloading of the SE (Thorpe and Minchin, 1987). The composition of phloem sap is not constant and can vary between day and night, for example, in barley (Hordeum vulgare; Winter et al, 1992), grapevine (Vitis vinifera; Gholami et al, 2004), and Ricinus (Smith and Milburn, 1980). In lupin (Lupinus spp.…”

mentioning

confidence: 99%

A Diurnal Component to the Variation in Sieve Tube Amino Acid Content in Wheat

et al. 2008

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We have used high-sensitivity capillary electrophoresis coupled to a laser-induced fluorescence detection method to quantify 16 amino acids in wheat (Triticum aestivum) sieve tube (ST) samples as small as 2 nL collected by severing the stylets of feeding aphids. The sensitivity of the method was sufficient to determine a quantitative amino acid profile of individual STs without the need to bulk samples to produce larger volumes for analysis. This allowed the observation of the full range of variation that exists in individual STs. Some of the total concentrations of amino acids recorded are higher than those reported previously. The results obtained show variation in the concentrations of phenylalanine (Phe), histidine/valine (His/Val), leucine/ isoleucine (Leu/Ile), arginine, asparagine, glutamine, tyrosine (Tyr), and lysine (Lys) across the ST samples. These could not be explained by plant-to-plant variation. Statistical analyses revealed five analytes (Tyr, Lys, Phe, His/Val, and Leu/Ile) that showed striking covariation in their concentrations across ST samples. A regression analysis revealed a significant relationship between the concentrations of Tyr, Lys, Phe, Leu/Ile, His/Val, asparagine, arginine, and proline and the time of collection of ST samples, with these amino acids increasing in concentration during the afternoon. This increase was confirmed to occur in individual STs by analyzing samples obtained from stylet bundles exuding for many hours. Finally, an apparent relationship between the exudation rate of ST sap and its total amino acid concentration was observed: samples containing higher total amino acid concentrations were observed to exude from the severed stylet bundles more slowly.

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“…Potassium concentrations have been found to reach values as high as 3/4 of the sucrose concentrations (Lang, 1983) which would correspond to maximum potassium loading rates of 1*10 -5 mol/s in our study. In addition, potassium can have additional important roles in phloem transport by aiding in the osmoregulation of turgor pressure under conditions of restricted solute availability (Smith and Milburn, 1980). Also, with lower sucrose concentrations, the role of potassium can be larger (Thompson and Zwieniecki, 2005).…”

Section: Effect Of Potassium On Phloem Transportmentioning

confidence: 99%

Linking phloem function to structure: Analysis with a coupled xylem–phloem transport model

Hölttä

Mencuccini

Nikinmaa

2009

Journal of Theoretical Biology

200

188

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Cite this article as: T. Hölttä, M. Mencuccini and E. Nikinmaa, Linking phloem function to structure: Analysis with a coupled xylem-phloem transport model, Journal of Theoretical Biology (2009Biology ( ), doi:10.1016Biology ( /j.jtbi.2009 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. We carried out a theoretical analysis of phloem transport based on Münch hypothesis by developing a coupled xylem-phloem transport model. Results showed that the maximum sugar transport rate of the phloem was limited by solution viscosity and that transport requirements were strongly affected by prevailing xylem water potential. The minimum number of xylem and phloem conduits required to sustain transpiration and assimilation, respectively, were calculated. At its maximum sugar transport rate, the phloem functioned with a high turgor pressure difference between the sugar sources and sinks but the turgor pressure difference was reduced if additional parallel conduits were added or solute relays were introduced. Solute relays were shown to decrease the number of parallel sieve tubes needed for phloem transport, leading to a more uniform turgor pressure and allowing faster information transmission within the phloem. Because xylem water potential affected both xylem and phloem transport, the conductance of the two systems was found to be coupled such that large structural investments in the xylem reduced the need for investment in the phloem and vice versa.

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Osmoregulation and the control of phloem-sap composition in Ricinus communis L.

Cited by 87 publications

References 25 publications

Arsenic Speciation in Phloem and Xylem Exudates of Castor Bean

Arsenic Speciation in Phloem and Xylem Exudates of Castor Bean

A Diurnal Component to the Variation in Sieve Tube Amino Acid Content in Wheat

Linking phloem function to structure: Analysis with a coupled xylem–phloem transport model

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