Quantitative Analysis of Photosynthate Unloading in Developing Seeds of <i>Phaseolus vulgaris</i> L.

Ellis, Erle C.; Turgeon, Robert; Spanswick, Roger M.

doi:10.1104/pp.99.2.643

Cited by 11 publications

(11 citation statements)

References 20 publications

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“…5A, C). This concurs with the finding that there was no significant difference in sugar efflux between attached and detached seed coats of P. vulgaris during the first 2 h of treatment with a low apoplastic osmolality (Ellis et al 1992). The initial assimilate etttux might occur from storage pools within the coat (Patrick 1993a), implying that short-term assimilate import through phloem has little influence on assimilate efflux during turgot regulation.…”

Section: Discussionsupporting

confidence: 84%

Turgor-dependent efflux of assimilates from coats of developing seed of Phaseolus vulgaris L.: water relations of the cells involved in efflux

Zhang

Atwell

Patrick

et al. 1996

Planta

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Abstract.The turgor-homeostat model of assimilate efflux from coats of developing seed of Phaseolus vulgaris L. was further characterised. The turgor pressure (P), the volumetric elastic modulus (~) and hydraulic conductivity (Lp) of the seed coat cells responsible for assimilate efttux and cotyledon storage parenchyma cells were determined with a pressure probe. In addition, turgor of the seed coat and cotyledons was estimated by measuring the osmolalities of symplastic and apoplastic fluids extracted by centrifugation. Osmolality of symplastic and apoplastic saps collected from the seed coat declined significantly over the period of seed development from a cotyledon water content of 80% to 50%. However, the difference in osmolalities of the apoplastic and symplastic saps remained relatively constant. For cotyledons, osmolality of the apoplastic sap exhibited a significant decline during seed development, while the osmolality of symplastic sap did not change significantly. Hence cotyledon P increased as the water content dropped from 80% to 50%. For both detached and attached 'empty' seed coats, a small decrease (ca. 40 mOsmol-kg-1) in the osmolality of the bathing solution, led to a rapid increase in P of cells involved in assimilate effiux (efflux cells) by about 0.07 MPa. Thereafter, cell P exhibited a rapid decline to the original value within some 20-30 min. When P of the 'efllux cells' was reduced by increasing the osmolality of the bathing solution, P exhibited a comparable rate of recovery for attached 'empty' seed coats but there was no P recovery to its original value in the case of detached seed coats. In contrast, the cotyledon storage parenchyma cells did not exhibit P regulation when the osmolality of the bathing solution was changed. The observations that the 'efftux cells' of P. vulgaris seed coats can rapidly adjust their P homeostatically in response to small changes in apoplastic osmolality are consistent with the operation of Abbreviations: LYCH = Lucifer Yellow CH; e = volumetric elastic modulus; Lp = hydraulic conductivity; P = turgor pressure; n = osmotic pressure; t~/2 = half-time for water exchange Correspondence to: J.W. Patrick; FAX: 61 (49) 216923; E-mail: bijwp@cc.newcastle.edu.au a turgor-homeostat mechanism. The volumetric elastic modulus (e) of the seed coat 'efltux cells' exhibited a mean value of 7.3 _+ 0.8 MPa at P --0.15 MPa and was found to be linearly dependent on cell P. The e of the cotyledon storage parenchyma cells was estimated to be 6.1 __ 1.0 MPa at P = 0.41 MPa. Hydraulic conductivity (Lp) of the seed coat cells and the cotyledon cells was (8.2 ___ 1.5) x 10 -8 m.s-l.MPa-land (12.8 _ 1.0)x 10 -s m-s-~-MPa -1, respectively. The relatively high e, i.e., low elasticity, for the seed coat cell walls would ensure that small changes in water potential of the seed apoplast will be reflected in large changes in cell P. The high Lp values for both the seed coat and the cotyledon cells is consistent with the rapid changes in P in response to changes in water potential of the s...

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Section: Discussionsupporting

confidence: 84%

Turgor-dependent efflux of assimilates from coats of developing seed of Phaseolus vulgaris L.: water relations of the cells involved in efflux

Zhang

Atwell

Patrick

et al. 1996

Planta

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show abstract

“…Involvement of the coat symplast is corroborated by reports of relatively high sugar specific activities in both intact and perfused coats of Phaseolus (Ellis et al 1992) and of asymmetrical distribution and rapid transport of 14c-labelled photosynthates in the non-vascularised regions of coats of Pisum . Evidence for a "Abbreviations used: CCCP, carbonylcyanide m-chlorophenylhydrazone; CF, 5-(6)-carboxyfluorescein; CFDA, 5-(6)-carboxyfluorescein diacetate; FC, fusicoccin; LYCH, Lucifer yellow CH; PCMBS, p-chloromercuribenzenesulfonic acid; PD, potential difference; pmf, proton motive force; PTS, trisodium-3-hydroxy-5,8,1O-pyrenetrisulfonate; SRG, sulforhodamine G. functional symplast has been derived from the movement of phloem-imported CF .…”

Section: Grain Legumesmentioning

confidence: 61%

“…This condition is achieved when the osmolality of the bathing solution equates with the in vivo water potential of the seed (Gifford and Thorne 1985;Porter et al 1985;Wolswinkel 1992;Wolswinkel and Koerselman-Kooij 1992; Wang and Fisher 1 9 9 4~) . However, in some cases phloem import into, and efflux from, legume seed coats was found to decline 2 h after embryo removal (Minchin and Thorpe 1989;Ellis et al 1992). Not surprisingly, efflux from detached legume seed coats continually declines from the time of excision (Gifford and Thorne 1986;Ellis et al 1992), thus restricting their application to short-term transport studies.…”

Section: Experimental Systemsmentioning

confidence: 99%

“…However, in some cases phloem import into, and efflux from, legume seed coats was found to decline 2 h after embryo removal (Minchin and Thorpe 1989;Ellis et al 1992). Not surprisingly, efflux from detached legume seed coats continually declines from the time of excision (Gifford and Thorne 1986;Ellis et al 1992), thus restricting their application to short-term transport studies. For the attached system, mathematical models have been developed and refined (Minchin and Thorpe 1989) to distinguish phloem import from efflux to the seed apoplast.…”

Section: Experimental Systemsmentioning

confidence: 99%

“…For both configurations, care needs to be exercised in adjusting the osmolality of the bathing solution to approach that of the whole seed water potential. Exposure of the 'empty' seed coat to dilute bathing solutions can result in a slowing of phloem import (Wolswinkel 1 9 8 5~; Grusak and Minchin 1988;Ellis et al 1992) and a stimulation of efflux Ellis et al 1992). maternal and (6) filial generations of developing wheat grain.…”

Section: Experimental Systemsmentioning

confidence: 99%

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Post-Sieve Element Transport of Sucrose in Developing Seeds

Patrick¹,

Offler²

1995

Functional Plant Biol.

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Developing seeds of cereals and grain legumes have proven to be useful experimental models to examine post-sieve element assimilate transport in sink tissues. Morphologically, these seeds offer well-defined sinks in which the processes of sucrose import plus efflux and influx plus metabolism may be examined independently. In all cases, sucrose is delivered through the phloem to the maternal seed tissues. Unloading from the sieve element-companion cell complexes is symplastic. Subsequently, sucrose moves through a symplastic route to cells responsible for sucrose efflux to the seed apoplast. The efflux cells are located at, or near, the maternal/filial interface. Sucrose is retrieved from the seed apoplast by the outermost cell layers of the filial tissues. Subsequent transfer of sucrose to the sites of storage in the filial tissues is confined principally to a symplastic route. Sucrose efflux from the maternal tissues appears to be passive in cereals and energy dependent in grain legumes, possibly through a sucrose/proton antiport system. Sucrose influx across the plasma membranes of the filial cells is energy dependent and, for grain legumes, is energy coupled through a sucrose/proton symporter. Studies on the control of post-sieve element transport of sucrose have focused largely on the membrane transport steps. The role of phytohormones as modulators of sucrose transport is uncertain in grain legumes, efflux from the maternal cells could be regulated by rates of sucrose utilisation in the filial tissues through a turgor homeostat mechanism located in the efflux cells.

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Assimilate uptake and the regulation of seed development

et al. 1998

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Seed development is a series of events involving cell division, followed by cell differentiation and storage activity In legume cotyledons, cell differentiation starts in certain regions and gradually spreads to other parts, thereby building up developmental gradients The entire process appears to be subject to metabolic control The high hexose state of the premature legume embryo as controlled by seed coat-specific invertases favours cell division Differentiation is initiated when hexose decreases and sucrose increases Seed development occurs in a close interaction with seed metabolism and transport processes Movement of photoassimilates from the sieve tubes to the unloading region of the maternal seed tissue is symplasmic and controlled by plasmodesmal passage Sucrose uptake into Vicia faba cotyledons is mediated by a H+-sucrose symporter located in the outer epidermis which generates transfer cells Formation of the sucrose uptake system is induced during the early to mid-cotyledon stage by tissue contact with the maternal seed coat and is controlled by carbohydrate availability In contrast, a hexose transporter gene is also expressed in epidermal cells covering younger, mitotically active regions of the cotyledons The sucrose uptake system apparently generates the high sucrose state immediately preceding the storage phase Sucrose specifically induces storage-associated differentiation processes indicating a specific sucrose-dependent signalling pathway operating in maturing cotyledons Moreover, the mode of sucrose uptake — apoplasmic movement into the epidermal cells with subsequent symplasmic transfer to the storage parenchyma cells — appears to control coordinated cotyledon development Unlike sucrose, amino acid transport into legume cotyledons is passive during early development but at later stages when large amounts of storage proteins are synthesized an additional active uptake system is established to ensure a sufficient supply

show abstract

Quantitative Analysis of Photosynthate Unloading in Developing Seeds of Phaseolus vulgaris L.

Cited by 11 publications

References 20 publications

Turgor-dependent efflux of assimilates from coats of developing seed of Phaseolus vulgaris L.: water relations of the cells involved in efflux

Turgor-dependent efflux of assimilates from coats of developing seed of Phaseolus vulgaris L.: water relations of the cells involved in efflux

Post-Sieve Element Transport of Sucrose in Developing Seeds

Assimilate uptake and the regulation of seed development

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