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Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders

Plasmodesmata (PD) play a key role in loading of sugars into the phloem. In plant species that employ the so-called active symplasmic loading strategy, sucrose that diffuses into their unique intermediary cells (ICs) is converted into sugar oligomers. According to the prevalent hypothesis, the oligo...

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Autores principales: Liesche, Johannes, Schulz, Alexander
Formato: Online Artículo Texto
Lenguaje:English
Publicado: Frontiers Media S.A. 2013
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3685819/
https://www.ncbi.nlm.nih.gov/pubmed/23802006
http://dx.doi.org/10.3389/fpls.2013.00207
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author Liesche, Johannes
Schulz, Alexander
author_facet Liesche, Johannes
Schulz, Alexander
author_sort Liesche, Johannes
collection PubMed
description Plasmodesmata (PD) play a key role in loading of sugars into the phloem. In plant species that employ the so-called active symplasmic loading strategy, sucrose that diffuses into their unique intermediary cells (ICs) is converted into sugar oligomers. According to the prevalent hypothesis, the oligomers are too large to pass back through PD on the bundle sheath side, but can pass on into the sieve element to be transported in the phloem. Here, we investigate if the PD at the bundle sheath-IC interface can indeed fulfill the function of blocking transport of sugar oligomers while still enabling efficient diffusion of sucrose. Hindrance factors are derived via theoretical modeling for different PD substructure configurations: sub-nano channels, slit, and hydrogel. The results suggest that a strong discrimination could only be realized when the PD opening is almost as small as the sugar oligomers. In order to find model parameters that match the in vivo situation, we measured the effective diffusion coefficient across the interface in question in Cucurbita pepo with 3D-photoactivation microscopy. Calculations indicate that a PD substructure of several sub-nano channels with a radius around 7 Å, a 10.4 Å-wide slit or a hydrogel with 49% polymer fraction would be compatible with the effective diffusion coefficient. If these configurations can accommodate sufficient flux of sucrose into the IC, while blocking raffinose and stachyose movement was assessed using literature data. While the slit-configuration would efficiently prevent the sugar oligomers from “leaking” from the IC, none of the configurations could enable a diffusion-driven sucrose flux that matches the reported rates at a physiologically relevant concentration potential. The presented data provides a first insight on how the substructure of PD could enable selective transport, but indicates that additional factors are involved in efficient phloem loading in active symplasmic loading species.
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spelling pubmed-36858192013-06-25 Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders Liesche, Johannes Schulz, Alexander Front Plant Sci Plant Science Plasmodesmata (PD) play a key role in loading of sugars into the phloem. In plant species that employ the so-called active symplasmic loading strategy, sucrose that diffuses into their unique intermediary cells (ICs) is converted into sugar oligomers. According to the prevalent hypothesis, the oligomers are too large to pass back through PD on the bundle sheath side, but can pass on into the sieve element to be transported in the phloem. Here, we investigate if the PD at the bundle sheath-IC interface can indeed fulfill the function of blocking transport of sugar oligomers while still enabling efficient diffusion of sucrose. Hindrance factors are derived via theoretical modeling for different PD substructure configurations: sub-nano channels, slit, and hydrogel. The results suggest that a strong discrimination could only be realized when the PD opening is almost as small as the sugar oligomers. In order to find model parameters that match the in vivo situation, we measured the effective diffusion coefficient across the interface in question in Cucurbita pepo with 3D-photoactivation microscopy. Calculations indicate that a PD substructure of several sub-nano channels with a radius around 7 Å, a 10.4 Å-wide slit or a hydrogel with 49% polymer fraction would be compatible with the effective diffusion coefficient. If these configurations can accommodate sufficient flux of sucrose into the IC, while blocking raffinose and stachyose movement was assessed using literature data. While the slit-configuration would efficiently prevent the sugar oligomers from “leaking” from the IC, none of the configurations could enable a diffusion-driven sucrose flux that matches the reported rates at a physiologically relevant concentration potential. The presented data provides a first insight on how the substructure of PD could enable selective transport, but indicates that additional factors are involved in efficient phloem loading in active symplasmic loading species. Frontiers Media S.A. 2013-06-19 /pmc/articles/PMC3685819/ /pubmed/23802006 http://dx.doi.org/10.3389/fpls.2013.00207 Text en Copyright © 2013 Liesche and Schulz. http://creativecommons.org/licenses/by/3.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in other forums, provided the original authors and source are credited and subject to any copyright notices concerning any third-party graphics etc.
spellingShingle Plant Science
Liesche, Johannes
Schulz, Alexander
Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders
title Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders
title_full Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders
title_fullStr Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders
title_full_unstemmed Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders
title_short Modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders
title_sort modeling the parameters for plasmodesmal sugar filtering in active symplasmic phloem loaders
topic Plant Science
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3685819/
https://www.ncbi.nlm.nih.gov/pubmed/23802006
http://dx.doi.org/10.3389/fpls.2013.00207
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