Phloem loading in peach: Symplastic or apoplastic?

Moing, Annick; Carbonne, Francis; Zipperlin, Benedicte; Svanella, Laurence; Gaudillere, Jean-Pierre J.-P.

doi:10.1034/j.1399-3054.1997.1010306.x

Cited by 25 publications

(31 citation statements)

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“…At the same time, this ratio is much lower than those determined for apoplastic phloem loaders (e.g. 16 for spinach; Lohaus et al, 1995) and resembles the values estimated for the putative symplastic loaders peach (Prunus persica; 1.7; Moing et al, 1997) and melon (Cucumis melo; 0.7; Haritatos et al, 1996). The 2-fold concentration gradient is obviously easier to smooth down or even reverse, depending on the metabolic situation, than the much steeper gradients found in apoplastic phloem loaders, so the possibility of symplastic phloem loading of Suc by simple diffusion under some conditions cannot be completely ruled out.…”

Section: Comparison Of Sugar Concentrations In Cytoplasm Of Mesophyllmentioning

confidence: 82%

Phloem Loading in Two Scrophulariaceae Species. What Can Drive Symplastic Flow via Plasmodesmata?

et al. 2005

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To determine the driving forces for symplastic sugar flux between mesophyll and phloem, gradients of sugar concentrations and osmotic pressure were studied in leaf tissues of two Scrophulariaceae species, Alonsoa meridionalis and Asarina barclaiana. A. meridionalis has a typical symplastic configuration of minor-vein phloem, i.e. intermediary companion cells with highly developed plasmodesmal connections to bundle-sheath cells. In A. barclaiana, two types of companion cells, modified intermediary cells and transfer cells, were found in minor-vein phloem, giving this species the potential to have a complex phloem-loading mode. We identified all phloem-transported carbohydrates in both species and analyzed the levels of carbohydrates in chloroplasts, vacuoles, and cytoplasm of mesophyll cells by nonaqueous fractionation. Osmotic pressure was measured in single epidermal and mesophyll cells and in whole leaves and compared with calculated values for phloem sap. In A. meridionalis, a 2-fold concentration gradient for sucrose between mesophyll and phloem was found. In A. barclaiana, the major transported carbohydrates, sucrose and antirrhinoside, were present in the phloem in 22- and 6-fold higher concentrations, respectively, than in the cytoplasm of mesophyll cells. The data show that diffusion of sugars along their concentration gradients is unlikely to be the major mechanism for symplastic phloem loading if this were to occur in these species. We conclude that in both A. meridionalis and A. barclaiana, apoplastic phloem loading is an indispensable mechanism and that symplastic entrance of solutes into the phloem may occur by mass flow. The conditions favoring symplastic mass flow into the phloem are discussed.

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Section: Comparison Of Sugar Concentrations In Cytoplasm Of Mesophyllmentioning

confidence: 82%

Phloem Loading in Two Scrophulariaceae Species. What Can Drive Symplastic Flow via Plasmodesmata?

et al. 2005

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“…The pH-dependent activity of this transporter is coherent with the classification of other SUT1 as H + /sucrose symporters. Therefore, it is possible hypothesize that it mediates the phloem loading within leaves, carrying sucrose across the membrane together with protons.. As for other members of SUT1 family, this hypothesis is supported in peach by the absence of PpSUT1 transcription in fruit mesocarp, and by the existence of an apoplasmic loading pathway in leaves [68]. The dimerization of the transporter may be a post-translational modification that regulates the sucrose uptake into the cell, acting on the amount of protein exported from the ER towards the plasma membrane, as postulated by Krügel et al (2008).…”

Section: Page 11 Of 23mentioning

confidence: 86%

Expression of peach sucrose transporters in heterologous systems points out their different physiological role

et al. 2015

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“…Moreover, in walnut fruit, distinct unloading patterns have been found in two types of tissues: symplastic in seed and apoplastic in fleshy pericarp (Wu et al ). Although the possibility of apoplastic phloem loading through an active transport pathway has been hypothesized as the most important means of exporting carbohydrates from mature leaves in peach (Moing et al ), unloading mechanisms are still a source of debate. However, carrier‐mediated transport has been hypothesized for mesocarp of young peaches (Vizzotto et al ).…”

Section: Introductionmentioning

confidence: 99%

Sucrose transport and phloem unloading in peach fruit: potential role of two transporters localized in different cell types

Zanon

Falchi

Santi

et al. 2014

Physiologia Plantarum

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Several complex physiological processes, which include long-distance translocation in the phloem and unloading in sink tissues, govern the partitioning of sugars in economically important organs, such as peach fruit. In this study, we took advantage of a symplastic tracer, carboxyfluorescein (CF), providing evidence for an apoplastic sucrose transfer in the early (SI) and middle (SIII) phases of peach fruit development. Moreover, using a combination of in situ hybridization and laser microdissection-assisted expression analysis, three putative sucrose transporters encoding genes (PpSUT1, PpSUT2, PpSUT4) were transcriptionally analyzed to relate their expression with sucrose storage in this organ. Our study revealed that PpSUT2 and PpSUT4 are the genes predominantly expressed in fruit flesh, and the detailed analysis of their expression pattern in the different cell types enabled us to suggest a specialized role in sucrose distribution. Both PpSUTs transporters could be involved in the retrieval of sucrose lost from the symplastic continuum of the phloem and, when expressed in parenchyma cells, they could be active in the import of sucrose into sink tissues, via symport from the apoplast. An alternative hypothesis has been proposed and discussed for PpSUT4 because of its putative tonoplastic localization. Taken together, our results provide new insights into the molecular mechanisms underpinning sucrose unloading and accumulation in peach fruit.

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Phloem loading in peach: Symplastic or apoplastic?

Cited by 25 publications

References 0 publications

Phloem Loading in Two Scrophulariaceae Species. What Can Drive Symplastic Flow via Plasmodesmata?

Phloem Loading in Two Scrophulariaceae Species. What Can Drive Symplastic Flow via Plasmodesmata?

Expression of peach sucrose transporters in heterologous systems points out their different physiological role

Sucrose transport and phloem unloading in peach fruit: potential role of two transporters localized in different cell types

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