Diffusion or bulk flow: how plasmodesmata facilitate pre-phloem transport of assimilates

Schulz, Alexander

doi:10.1007/s10265-014-0676-5

Cited by 42 publications

(27 citation statements)

References 76 publications

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“…Indications for passive symplasmic loading are given for many woody angiosperms and for all gymnosperms. The prephloem pathway of the latter is however much more complex (Canny, 1993;Liesche, Martens, and Schulz, 2011;Schulz, 2014).…”

Section: Passive Symplasmic Loadingmentioning

confidence: 99%

“…Passive symplasmic loading seems in a way quite energy efficient, since no additional energy is needed in the phloem itself, and the highest sugar concentration is where it is produced. For the overall transport process from mesophyll via the phloem to the sink organs, it is an interesting question where the purely diffusive sucrose transport starts to be converted into a bulk flow: already on the prephloem pathway or only in the phloem (Schulz, 2014). Indications for passive symplasmic loading are given for many woody angiosperms and for all gymnosperms.…”

Section: Passive Symplasmic Loadingmentioning

confidence: 99%

“…From Münch, 1930, p. 153. allowing the plant to have a highly concentrated phloem without an equally high concentration in the leaves, which would make the latter very attractive for unwanted foragers. The feasibility of this loading strategy was recently analyzed by Dölger et al (2014) based on the best available data from the melon Cucumis melo (Schmitz, Cuypers, and Moll, 1987;Haritatos, Keller, and Turgeon, 1996;Volk, Turgeon, and Beebe, 1996); see also the recent review by Schulz (2014). The geometry of the problem is sketched in Fig.…”

Section: B Conduit Optimizationmentioning

confidence: 99%

“…Sugars and amino acids to be translocated long distance in the phloem must first be transported from mesophyll cell to mesophyll cell into the bundle sheath. This prephloem transport of assimilates, with sucrose as the most important representative of sugars, follows the distribution of plasmodesmata in the cell wall interfaces (Schulz, 2014). A simplified model on active apoplasmic loading is shown in Fig.…”

Section: Active Apoplasmic Loadingmentioning

confidence: 99%

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Sap flow and sugar transport in plants

et al. 2016

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Green plants are Earth's primary solar energy collectors. They harvest the energy of the Sun by converting light energy into chemical energy stored in the bonds of sugar molecules. A multitude of carefully orchestrated transport processes are needed to move water and minerals from the soil to sites of photosynthesis and to distribute energy-rich sugars throughout the plant body to support metabolism and growth. The long-distance transport happens in the plants' vascular system, where water and solutes are moved along the entire length of the plant. In this review, the current understanding of the mechanism and the quantitative description of these flows are discussed, connecting theory and experiments as far as possible. The article begins with an overview of low-Reynolds-number transport processes, followed by an introduction to the anatomy and physiology of vascular transport in the phloem and xylem. Next, sugar transport in the phloem is explored with attention given to experimental results as well as the fluid mechanics of osmotically driven flows. Then water transport in the xylem is discussed with a focus on embolism dynamics, conduit optimization, and couplings between water and sugar transport. Finally, remarks are given on some of the open questions of this research field.

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Section: Passive Symplasmic Loadingmentioning

confidence: 99%

Section: Passive Symplasmic Loadingmentioning

confidence: 99%

Section: B Conduit Optimizationmentioning

confidence: 99%

Section: Active Apoplasmic Loadingmentioning

confidence: 99%

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Sap flow and sugar transport in plants

et al. 2016

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“…Such PPUs form the decisive interface between the stationary phase in CCs and the mobile phase of the "running river" in sieve tubes (Sjolund, 1997). It is a prerequisite for phloem loading and transport that PPUs in minor vein phloem are able to convey sugars and other small molecules freely (Schulz, 2015). However, active phloem loading at the same time depends on retention of energy-rich compounds formed in CCs (UDP-galactose and ATP, respectively; Beebe and Turgeon, 1992;DeWitt and Sussman, 1995).…”

Section: Mobility Of Macromolecules Formed In Companion Cellsmentioning

confidence: 99%

Long-Distance Trafficking: Lost in Transit or Stopped at the Gate?

Schulz

2017

Plant Cell

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Plasmodesmata

Faulkner

Oparka

2016

Encyclopedia of Life Sciences

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Plasmodesmata are plasma membrane‐lined pores that span the adjoining walls of plant cells. They permit the intercellular passage of molecules and signals and play a central role in plant physiology and development. Evidence suggests that small molecules can pass from cell to cell by passive diffusion and that this is controlled by regulation of the pore itself. This contributes to processes such as the transport of sugars between cells and tissues. Many endogenous plant proteins and ribonucleic acid (RNA)‐based signals also utilise plasmodesmata for cell‐to‐cell and long‐distance movement. Recent data suggests that plasmodesmata are tightly controlled during development and in response to environmental changes. There is increasing evidence that this regulation is controlled by proteins that have specific plasmodesmata‐associated functions in stimulus perception and signalling. In addition, many viruses exploit plasmodesmata for cell‐to‐cell spread during infection and their encoded viral movement proteins manipulate the pores to facilitate this process. Key Concepts Plant cells are connected to each other by cytoplasmic bridges called plasmodesmata. The continuous interconnected cytoplasm in plants is referred to as the symplasm. A tube of endoplasmic reticulum passes through plasmodesmata and connects the endoplasmic reticulum of neighbouring cells, thus providing endomembrane continuity between cells. Primary plasmodesmata are formed at cytokinesis when strands of endoplasmic reticulum are trapped between fusing vesicles in the developing cell wall. Secondary plasmodesmata are formed across existing cell walls, including those at graft unions, and usually arise immediately adjacent to existing plasmodesmata. Molecules smaller than the size exclusion limit (SEL) of plasmodesmata are able to move freely through the cytoplasmic channel of plasmodesmata by simple diffusion. The SEL of plasmodesmata may increase or decrease to allow changes in plasmodesmatal conductance. This may occur under different conditions, for example, in response to intracellular factors such as cytoplasmic calcium levels or pathogen perception. Some endogenous proteins and some movement proteins encoded by plant viruses are able to increase the SEL of plasmodesmata to facilitate their own passage into neighbouring cells. This enables these proteins to function in cells in which they are not normally expressed. Groups of cells may be connected by plasmodesmata that share an SEL different to that of neighbouring cells. These regions of cells are called symplasmic domains. Some proteins and RNA molecules pass into the plant's translocation stream and move over long distances. These macromolecules traffic through the plasmodesmata that join sieve elements (SE) and companion cells within the phloem. These macromolecules may have a site of action distant to their site of expression and synthesis.

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Diffusion or bulk flow: how plasmodesmata facilitate pre-phloem transport of assimilates

Cited by 42 publications

References 76 publications

Sap flow and sugar transport in plants

Sap flow and sugar transport in plants

Long-Distance Trafficking: Lost in Transit or Stopped at the Gate?

Plasmodesmata

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