Intercellular communication inAzolla roots: I. Ultrastructure of plasmodesmata

Overall, Robyn L.; Wolfe, Joe; Gunning, B. E. S.

doi:10.1007/bf01282071

Cited by 129 publications

(73 citation statements)

References 40 publications

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“…However, recent work on plasmodesmatal ultrastructure (Overall et al, 1982; Ding et al, 1992) and on symplasmic transport using fluorescently labeled tracers of different sizes Goodwin, 1983, 1985; Terry and Robards, 1987) suggests that the transport capacity of plasmodesmata is significantly less than was previously believed. In addition, these previous models did not account for the transport demands imposed by growth in a multicellular organ.…”

mentioning

confidence: 96%

“…Terry and Robards (1987) tested an extensive range of fluorescent probes of different sizes and concluded that molecules with a Stokes' radius of 0.9 nm approach the molecular exclusion limit for plasmodesmata in Abutilon nectary cells, which is consistent with channels through the ultrastructure 2 to 3 nm in diameter. Although none of these workers were using maize root-tip cells, the ultrastructural particles that are thought to be the cause of these exclusion limits have been seen in plasmodesmata from a variety of plant organs and species and are believed to be of general occurrence (Overall et al, 1982;Robards and Lucas, 1990;Ding et al, 1992).…”

Section: Alternative Calculation Of the Apparent Diffusion Coefficienmentioning

confidence: 99%

“…The conductance of one plasmodesma can be calculated from the dimensions of the pore, as was done by Tyree (1970), except that it is now thought that the "necks" and possibly the entire length of the cytoplasmic pores of plasmodesmata are partially occluded by ultrastructural particles that greatly reduce the effective cross-sectional area of the pores (Overall et al, 1982;Ding et al, 1992). Plasmodesmatal pores may be capable of further constriction under some circumstances (Robards and Lucas, 1990).…”

Section: Determination Of Symplasmic Diffusivitymentioning

confidence: 99%

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Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

1994

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Nonvascular, symplasmic transport of sucrose (Suc) was investigated theoretically in the primary root tip of maize (Zea mays 1.cv WF9 x Mo 17) seedlings. Symplasmic diffusion has been assumed to be the mechanism of transport of Suc to cells in the root apical meristem (R.T. Ciaquinta, W. Lin, N.L. Sadler, V.R. Franceschi [1983] Plant Physiol 72: 362-367), which grow apical to the end of the phloem and must build all biomass with carbon supplied from the shoot or kernel. We derived an expression for the growthsustaining Suc flux, which is the minimum longitudinal flux that would be required to meet the carbon demands of growth in the root apical meristem. We calculated this flux from data on root growth velocity, area, and biomass density, taking into account construction and maintenance respiration and the production of mucilage by the root cap. We then calculated the conductivity of the symplasmic pathway for diffusion, from anatomical data on cellular dimensions and the frequency and dimensions of plasmodesmata, and from two estimates of the diffusive conductance of a plasmodesma, derived from independent data. Then, the concentration gradients required to drive a growth-sustaining Suc flux by diffusion alone were calculated but were found not to be physiologically reasonable. We also calculated the hydraulic conductivity of the plasmodesmatal pathway and found that mass flow of Suc solution through plasmodesmata would also be insufficient, by itself, to satisfy the carbon demands of growth. However, much of the demand for water to cause cell expansion could be met by the water unloaded from the phloem while unloading Suc to satisfy the carbon demands of growth, and the hydraulic conductivity of plasmodesmata is high enough that much of that water could move symplasmically. Either our current understanding of plasmodesmatal ultrastructure and function is flawed, or alternative transport mechanisms must exist for Suc transport to the meristem.Understanding the control of plant growth and development must include an understanding of the transport of photoassimilates from sources into developing sinks. Transport of solutes through the differentiated phloem is explained well by quantitative treatments of Miinch's (1930) pressure flow hypothesis (Christy and Femer, 1973;Tyree et al., 1974a;Ross and Tyree, 1980), and experimental data are in reasonably good agreement with their predictions (cf. Zimmermann and Brown, 1971; Pickard et al.,

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mentioning

confidence: 96%

Section: Alternative Calculation Of the Apparent Diffusion Coefficienmentioning

confidence: 99%

Section: Determination Of Symplasmic Diffusivitymentioning

confidence: 99%

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Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

1994

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“…lncorporated within this plasmalemma-delimited gap is the dominant transwall structural component of plasmodesmata called the desmotubule (Robards, 1976). Considerable efforts utilizing transmission electron microscopy have been dedicated to elucidating the structure and composition of the desmotubule (Lopez-Saez et al, 1966;Robards, 1968;Overall et al, 1982;Robards and Lucas, 1990), but as pointed out by Tilney et al (1991), the interpretations of structure "have changed repeatedly backwards and forwards." Suggestions for organization have varied between descriptions of a lipid-containing tubule connected to endoplasmic reticulum (ER) (Lopez-Saez et al, ' To whom correspondence should be addressed.…”

Section: Introductionmentioning

confidence: 99%

“…1966; Overall et al, 1982) to the structure of a microtubulelike rod composed of protein subunits (Robards, 1968). Difficulties in the interpretation of transmission electron microscopy images have been ascribed to the relatively small size of the structure, the inability to isolate plasmodesmata from plant tissue, and the "Draconian" methods available to microscopists (Tilney et al, 1991).…”

Section: Introductionmentioning

confidence: 99%

Endoplasmic Reticulum Forms a Dynamic Continuum for Lipid Diffusion between Contiguous Soybean Root Cells.

1993

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lntercellular communication between plant cells for low molecular weight hydrophilic molecules occurs through plasmodesmata. These tubular structures are embedded in the plant cell wall in association with the plasmalemma and endoplasmic reticulum (ER). Transmission electron microscopy has provided strong evidence to support the view that both the ER and plasmalemma are structurally continuous across the wall at these sltes. In experiments to be described, the technique of fluorescence redistribution after photobleaching was used to examine the lateral mobility and intercellular transport capability of a number of fluorescent lipid and phospholipid analogs. These probes were shown by confocal fluorescence microscopy to partition in either the ER or plasmalemma. Results from these measurements provide evidente for cell communication between contiguous cells for probes localized predominantly in the ER. In contrast, no detectable intercellular communication was obsenred for probes residing exclusively in the plasmalemma. It was of particular interest to note that when 1-acyl-2-(N-4-nitrobenzod-oxa-l,3-diazole)aminoacylphosphatidylchoIine was utilized as a potential reporter molecule for phospholipids in the plasmalemma, it was quickly degraded to l-acyI-2-(N-4-nitrobenzo-P-oxa-l,3-diarole)aminoacyldiglyceride (NBD-DAG), which then appeared predominantly localized to the ER and nuclear envelope. This endogenously synthesized NBD-DAG was found to be capable of transfer between cells, as was exogenously incorporated NBD-DAG. Results from these investigations provide support for the following conclusions: (1) ER, but apparently not the plasmalemma, can form dynamic communication pathways for lipids across the cell wall between connecting plant cells; (2) the plasmodesmata appear to form a barrier for lipid diffusion through the plasmalemma; and (3) lipid signaling molecules such as diacylglycerol are capable of transfer between contiguous plant cells through the ER. These observations speak to issues of plant cell autonomy for lipid synthesis and mechanisms of intercellular signaling and communication.

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Plasmodesmal Structure and Development

Roberts¹

2005

Plasmodesmata

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Intercellular communication inAzolla roots: I. Ultrastructure of plasmodesmata

Cited by 129 publications

References 40 publications

Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

Nonvascular, Symplasmic Diffusion of Sucrose Cannot Satisfy the Carbon Demands of Growth in the Primary Root Tip of Zea mays L

Endoplasmic Reticulum Forms a Dynamic Continuum for Lipid Diffusion between Contiguous Soybean Root Cells.

Plasmodesmal Structure and Development

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