Phloem unloading and turgor‐sensitive transport: Factors involved in sink control of assimilate partitioning

Wolswinkel, P.

doi:10.1111/j.1399-3054.1985.tb02404.x

Cited by 77 publications

(58 citation statements)

References 81 publications

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“…Sugar uptake into cells has been repeatedly shown to be turgor-dependent: within limits, lowering of turgor stimulates uptake (for reviews see Wolswinkel, 1985Wolswinkel, , 1990Daie, 1988; Lucas & Madore, 1988 ;Tomos, 1988;Patrick, 1990). The underlying mechanisms are not very well understood.…”

Section: Turgor-dependencementioning

confidence: 99%

Carbohydrate transport in discs of storage parenchyma of celery petioles

Keller

1991

New Phytologist

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SUMMARYThe sugar alcohol mannitol is, together with glucose and fructose, the main soluble carbohydrate of celery petioles. It is accumulated in the storage parenchyma of mature petioles and remobilized during senescence. The mechanisms of mannitol uptake into discs isolated from petiole parenchyma was studied. Uptake kinetics showed a biphasic response to increasing external concentrations of ["ClD-mannitol with a predominant saturable component at low concentrations (below about 2 mM) and a linear component at higher concentrations (at least up to 16 mM). The saturable component showed an apparent K^^^ of about 1 mM and a fairly sharp pH optimum around pH 6-5. It was stimulated by the plasmalemma H+-ATPase stimulator FC and inhibited by the SHreagents PCMBS and NEM and the uncoupler DNP. CCCP was also inhibitory, but its effect could be reversed by DTT, suggesting a dual role of CCCP as SH-reagent and uncoupler in this tissue. Competition studies with 14-different polyols and sugars showed that uptake was very specific. The saturable uptake component was clearly turgor-dependent. Lowering of cell turgor by treatment of increasing concentrations of the relatively nonpermeant glycinebetaine (0 to 0-8 M) resulted in a linear increase of V^^,^ and an unaltered K^.It is concluded that celery petiole parenchyma contains at least a mannitol carrier at the plasmalemma which operates in an active proton-cotransport manner. It is speculated that a superimposed mannitol carrier is present at the tonoplast and might operate by facilitated diffusion.

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Section: Turgor-dependencementioning

confidence: 99%

Carbohydrate transport in discs of storage parenchyma of celery petioles

Keller

1991

New Phytologist

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“…The rate of photosynthate "unloading" from seed coats ofPhaseolus vulgaris depends on cell turgor potential (17). In developing seeds from Vicia faba and Pisum sativum, the release of sucrose and of amino acids from the seed coat is sensitive to the osmolality of the bathing solution while phosphate release is unaffected by these solutions (23,24). However, the rate of unloading in seed coats of developing soybean seeds 'Supported by the Centre National de la Recherche Scientifique (UA 574).…”

Section: Abstracimentioning

confidence: 99%

Osmotic Dependence of the Transmembrane Potential Difference of Broadbean Mesocarp Cells

Li¹,

Delrot²

1987

Plant Physiol.

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ABSTRACIPod walls of broadbean (Viciafaba L. cv Aguadulce) were harvested at the import (54) at the transition (S2) or at the export (S3) phase for assimilate transport. Measurements of the transmembrane potential difference (PD) of mesocarp cells were made under various osmotic conditions. Internal osmotic potentials and cell turgor were calculated from osmolality measurements of cell saps recovered by freeze-thawing, after correction for the contribution of the free-space solution. Changes in the mannitol concentration of the medium altered the PD within a few minutes, and new stable values of PD were reached within 20 minutes after the osmotic change. With mannitol as the osmoticum, the most negative PD was measured at an external osmotic potential of -0.70 megapascls (MN) for SI and S2, while the most negative was at -0.40 MPa for S3. Ethylene glycol, a permeant osmoticum, had little effect on PD, showing that the PD was sensitive to turgor, not to solute potential per se. For SI and S2, the PD was less negative for turgor potentials lower than 0.1 MPa or greater than 03 MPa. S3 samples exhibited a different turgor dependence, with a sharp optimum of the negativity of the PD at 03 MPa. The data are consistent with the proposal that the proton pump acts as a transducer of the osmotic conditions. They show that the osmotic sensitivity of the PD of mesocarp cells of broadbean changes with the stage of development of the pod. Transport processes at the cell level in the sources and in the sinks of a plant depend on the osmotic environment (2-3, 5, 6, 12, 20, 23, 24). The proton-pumping activity of leaf tissues, as measured by the rate ofacidification oftheir incubation medium, is influenced by the osmotic potential ofthis medium (3,19,25). The uptake of exogenous sugars and amino acids by the leaf is also affected by the concentration and the nature of the osmoticum (2,8,9). Evidence has been given that, in leaf tissues of Phaseolus coccineus, the osmotic conditions altered sucrose uptake, and more particularly its saturable component, via changes in cell turgor (1). Several data suggest that the rate of assimilate transport may also be controlled by the osmotic environment in sink tissues. The rate of photosynthate "unloading" from seed coats ofPhaseolus vulgaris depends on cell turgor potential (17). In developing seeds from Vicia faba and Pisum sativum, the release of sucrose and of amino acids from the seed coat is sensitive to the osmolality of the bathing solution while phosphate release is unaffected by these solutions (23,24). However, the rate of unloading in seed coats of developing soybean seeds 'Supported by the Centre National de la Recherche Scientifique (UA 574).2Supported by a grant from the People's Republic of China.is not affected by mannitol concentrations up to 500 mm (17). In sugar beet taproot tissue, the saturable component of sucrose uptake is sensitive to turgor (25).At the whole plant level, according to the mass-flow model (14), long distance transport also depends on the establishme...

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“…Assimilate import into the ovules of legumes, the most extensively studied species, increases with increasing apoplastic osmotic concentration. Since these treatments presumably alter phloem turgor, apoplast osmotic concentration has been suggested as a possible control factor for solute import into developing seeds (Wolswinkel, 1985(Wolswinkel, , 1990Patrick, 1990). Also, several workers have shown that solute release from legume seed coats is metabolically dependent (Patrick, 1983;Wolswinkel and Ammerlaan, 1983;Gifford and Thome, 1986), suggesting the possible involvement of an active transport step(s).…”

mentioning

confidence: 99%

Monitoring Phloem Unloading and Post-Phloem Transport by Microperfusion of Attached Wheat Grains

Wang

Fisher

1994

Plant Physiol.

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Phloem unloading and post-phloem transport in developing wheat (Trificum aestivum 1.) grains were investigated by perfusing the endosperm cavities of attached grains. Relative unloading ratio (RUR) and the rate of sucrose release into the endosperm cavity (SRR) were calculated, respectively, from 14C import and from sucrose washout from the cavity. RUR and SRR continued at or near in vivo rates over a wide range of cavity sap osmolality (90 to approximately 500 milliosmolal) and sucrose concentration (14-430 mM) and for long times (29 h). These are much greater ranges than have been observed for the endosperm cavity in vivo (230-300 milliosmolal, and 40-120 mM, respectively), indicating that neither the cavity sap osmolality nor sucrose concentration are controlling factors for the rate of assimilate import into the cavity. The maintenance of in vivo transport rates over a wide range of conditions strongly implicates the role of transport processes within the maternal tissues of the wheat grain, rather than activities of the embryo or endosperm, in determining the rate of assimilate import into the grain. RUR was decreased by high concentrations of sucrose and sorbitol, but not of mannitol. By plasmolyzing some chalazal cells, sorbitol appeared to block symplastic transport across the crease tissues, but neither sucrose nor mannitol caused plasmolysis in maternal tissues of attached grains. The inhibition of RUR by KCN and carbonyl cyanide m-chlorophenyl (CCCP) and the continued import of sucrose into grains against its concentration gradient suggest that solute movement into the endosperm cavity might occur by active membrane transport. However, the evidence is weak, since KCN and CCCP appeared to act primarily on some aspect of symplastic (i.e. nonmembrane) transport. Also, sucrose could move from the endosperm cavity into the maternal tissues (i.e. opposite to the normal direction of sucrose movement), suggesting that transmembrane movement in the nucellus may be a reversible process. Pressure-driven flow into the grain could account for movement against a concentration gradient.

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Phloem unloading and turgor‐sensitive transport: Factors involved in sink control of assimilate partitioning

Abstract: Wolswinkel, P. 1985. Phloem unloading and turgor-sensitive transport: Factors involved in sink control of assimilate partitionhig. -Physiol. Plant. 65: 331-339.Additional key words -Phloem transport, pressure-flow mechanism, seed development, sink strength, source-sink relation.

Cited by 77 publications

References 81 publications

Carbohydrate transport in discs of storage parenchyma of celery petioles

Carbohydrate transport in discs of storage parenchyma of celery petioles

Osmotic Dependence of the Transmembrane Potential Difference of Broadbean Mesocarp Cells

Monitoring Phloem Unloading and Post-Phloem Transport by Microperfusion of Attached Wheat Grains

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