Solute Transport in the Phloem

Pritchard, Jeremy

doi:10.1002/9780470988862.ch10

Cited by 11 publications

(19 citation statements)

References 212 publications

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“…The MVB phloem is involved in transport and unloading of photoassimilates, organic metabolic processes and long‐distance signaling. Signaling involves the transport of hormones, such as auxin, and macromolecules including RNA and protein (Friml and Palme, ; van Bel, ; Thorpe et al ., ; Pritchard, ; Turgeon and Wolf, ). Similar signaling functions of the IP of the MVB are implied by significantly enriched GO terms: ‘auxin polar transport’, ‘RNA transport’ and ‘protein transport’ (Table S3; Figure a).…”

Section: Discussionmentioning

confidence: 99%

“…Are there specific functions associated with the IP and EP in the fruit? The phloem has many roles in addition to nutrient transport, including synthesis and transport of hormones, defense compounds (Pritchard, 2007;Turgeon and Wolf, 2009), and macromolecules that play critical roles in plant growth and development (Petersen et al, 2005;Dinant and Lemoine, 2010;Kragler, 2010). However, information on specific functions of the IP and EP is limited.…”

Section: Introductionmentioning

confidence: 99%

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Transcriptomic and functional analysis of cucumber (Cucumis sativus L.) fruit phloem during early development

Sui

Nie

et al. 2018

The Plant Journal

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The phloem of the Cucurbitaceae has long been a subject of interest due to its complex nature and the economic importance of the family. As in a limited number of other families, cucurbit phloem is bicollateral, i.e. with sieve tubes on both sides of the xylem. To date little is known about the specialized functions of the internal phloem (IP) and external phloem (EP). Here, a combination of microscopy, fluorescent dye transport analysis, micro-computed tomography, laser capture microdissection and RNA-sequencing (RNA-Seq) were used to study the functions of IP and EP in the vascular bundles (VBs) of cucumber fruit. There is one type of VB in the peduncle, but four in the fruit: peripheral (PeVB), main (MVB), carpel (CVB) and placental (PlVB). The VBs are bicollateral, except for the CVB and PlVB. Phloem mobile tracers and C applied to leaves are transported primarily in the EP, and to a lesser extent in the IP. RNA-Seq data indicate preferential gene transcription in the IP related to differentiation/development, hormone transport, RNA or protein modification/processing/transport, and nitrogen compound metabolism and transport. The EP preferentially expresses genes for stimulus/stress, defense, ion transport and secondary metabolite biosynthesis. The MVB phloem is preferentially involved in photoassimilate transport, unloading and long-distance signaling, while the PeVB plays a more substantial role in morphogenesis and/or development and defense response. CVB and PlVB transcripts are biased toward development of reproductive organs. These findings provide an integrated view of the differentiated structure and function of the vascular tissue in cucumber fruit.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Transcriptomic and functional analysis of cucumber (Cucumis sativus L.) fruit phloem during early development

Sui

Nie

et al. 2018

The Plant Journal

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“…In the stem zone where the loss was higher, an active retrieval of older unlabeled carbon could have restored the sieve tube hydrostatic osmotic potential and hence pressure. In addition, other osmotica, such as potassium could play a role in regulating the phloem pressure (Thompson and Zwieniecki, 2005; Pritchard, 2007). …”

Section: Discussionmentioning

confidence: 99%

11C-PET imaging reveals transport dynamics and sectorial plasticity of oak phloem after girdling

et al. 2013

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Carbon transport processes in plants can be followed non-invasively by repeated application of the short-lived positron-emitting radioisotope 11C, a technique which has rarely been used with trees. Recently, positron emission tomography (PET) allowing 3D visualization has been adapted for use with plants. To investigate the effects of stem girdling on the flow of assimilates, leaves on first order branches of two-year-old oak (Quercus robur L.) trees were labeled with 11C by supplying 11CO2-gas to a leaf cuvette. Magnetic resonance imaging gave an indication of the plant structure, while PET registered the tracer flow in a stem region downstream from the labeled branches. After repeated pulse labeling, phloem translocation was shown to be sectorial in the stem: leaf orthostichy determined the position of the phloem sieve tubes containing labeled 11C. The observed pathway remained unchanged for days. Tracer time-series derived from each pulse and analysed with a mechanistic model showed for two adjacent heights in the stem a similar velocity but different loss of recent assimilates. With either complete or partial girdling of bark within the monitored region, transport immediately stopped and then resumed in a new location in the stem cross-section, demonstrating the plasticity of sectoriality. One day after partial girdling, the loss of tracer along the interrupted transport pathway increased, while the velocity was enhanced in a non-girdled sector for several days. These findings suggest that lateral sugar transport was enhanced after wounding by a change in the lateral sugar transport path and the axial transport resumed with the development of new conductive tissue.

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“…Phloem translocation is achieved by the hydraulically driven flow of sap through sieve tubes (Pritchard, 2007). Since SE osmotic pressure and whole plant phenotype was largely unchanged despite the large reduction in SE amino acid concentration, it is likely that the levels of other SE solutes (e.g.…”

Section: Discussionmentioning

confidence: 99%

A mutation in amino acid permease AAP6 reduces the amino acid content of the Arabidopsis sieve elements but leaves aphid herbivores unaffected

Hunt

Gattolin

Newbury

et al. 2009

Journal of Experimental Botany

129

118

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The aim of this study was to investigate the role of the amino acid permease gene AAP6 in regulating phloem amino acid composition and then to determine the effects of this altered diet on aphid performance. A genotype of Arabidopsis thaliana (L.) was produced in which the function of the amino acid permease gene AAP6 (At5g49630) was abolished. Plants homozygous for the insertionally inactivated AAP6 gene had a significantly larger mean rosette width than the wild type and a greater number of cauline leaves. Seeds from the aap6 mutant were also significantly larger than those from the wild-type plants. Sieve element (SE) sap was collected by aphid stylectomy and the amino acids derivatized, separated, and quantified using Capillary Electrophoresis with Laser Induced Fluorescence (CE-LIF). In spite of the large variation across samples, the total amino acid concentration of SE sap of the aap6 mutant plants was significantly lower than that of the wild-type plants. The concentrations of lysine, phenylalanine, leucine, and aspartic acid were all significantly lower in concentration in the aap6 mutant plants compared with wild-type plants. This is the first direct demonstration of a physiological role for an amino acid transporter in regulating SE composition in vivo. The amino acid availability in sieve element sap is thought to be the major limiting factor for aphid growth and reproduction. Despite the changes in their diet, the aphid Myzus persicae (Sulzer) displayed only small changes in feeding behaviour on mutant plants when measured using the Electronic Penetration Graph (EPG) technique. Salivation by the aphid into the SE (E1 phase) was increased on mutant plants but there was no significant effect on other feeding EPG behaviours, or in the rate of honeydew production. Consistent with the small effect on aphid feeding behaviour, there was only a small effect of reduced sieve element amino acid concentration on aphid reproduction. The data are discussed in relation to the regulation of phloem composition and the role of phloem amino acids in regulating aphid performance.

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Solute Transport in the Phloem

Cited by 11 publications

References 212 publications

Transcriptomic and functional analysis of cucumber (Cucumis sativus L.) fruit phloem during early development

Transcriptomic and functional analysis of cucumber (Cucumis sativus L.) fruit phloem during early development

11C-PET imaging reveals transport dynamics and sectorial plasticity of oak phloem after girdling

A mutation in amino acid permease AAP6 reduces the amino acid content of the Arabidopsis sieve elements but leaves aphid herbivores unaffected

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