Is Phloem Transport Due to a Hydrostatic Pressure Gradient? Supporting Evidence From Pressure Chamber Experiments

Minchin, P. E. H.; Thorpe,

doi:10.1071/pp9870397

Cited by 16 publications

(10 citation statements)

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“…This favours both xylem and phloem flows to the fruit (Lang and Thorpe, 1986;Minchin and Thorpe, 1987;Patrick, 1990Patrick, , 1997Minchin et al, 1996). Xylem inflow, in response to cuticle water losses, delivers water at rates high enough to support fruit enlargement.…”

Section: Discussionmentioning

confidence: 99%

“…Phloem and xylem flows are driven by turgor pressure and osmotic concentration gradients along the vascular path from source to sink organs (Münch, 1930;Minchin and Thorpe, 1987;Patrick, 1990Patrick, , 1997Minchin et al, 1996). In peach, diurnal patterns of leaf and fruit water potentials have been reported by McFadyen et al, (1996), who related changes in fruit growth rate over 24 h to shifting water potential gradients between fruit and leaves.…”

Section: Introductionmentioning

confidence: 99%

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Vascular flows and transpiration affect peach (Prunus persica Batsch.) fruit daily growth

Morandi

Rieger

Grappadelli

2007

Journal of Experimental Botany

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The relative contributions of xylem, phloem, and transpiration to fruit growth and the daily patterns of their flows have been determined in peach, during the two stages of rapid diameter increase, by precise and continuous monitoring of fruit diameter variations. Xylem, phloem, and transpiration contributions to growth were quantified by comparing the diurnal patterns of diameter change of fruits, which were then girdled and subsequently detached. Xylem supports peach growth by 70%, and phloem 30%, while transpiration accounts for ;60% of daily total inflows. These figures and their diurnal patterns were comparable among years, stages, and cultivars. Xylem was functional at both stage I and III, while fruit transpiration was high and strictly dependent on environmental conditions, causing periods of fruit shrinkage. Phloem imports were correlated to fruit shrinkage and appear to facilitate subsequent fruit enlargement. Peach displays a growth mechanism which can be explained on the basis of passive unloading of photoassimilates from the phloem. A pivotal role is played by the large amount of water flowing from the tree to the fruit and from the fruit to the atmosphere.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Vascular flows and transpiration affect peach (Prunus persica Batsch.) fruit daily growth

Morandi

Rieger

Grappadelli

2007

Journal of Experimental Botany

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“…However, an additional physiological consequence of high solutes in the apoplastic space is the maintenance of low turgor during sucrose accumulation (Moore and Cosgrove 1991). Low turgor within the sink would promote translocation of sucrose from the leaf by mass transfer in the phloem (Minchin and Thorpe 1987;Patrick 1991) to keep the storage tissue as an active sink (Wolswinkel 1985;Ho 1988;Patrick 1992).…”

Section: Stem Apoplast and Water Relationsmentioning

confidence: 99%

Temporal and Spatial Regulation of Sucrose Accumulation in the Sugarcane Stem

Moore¹

1995

Functional Plant Biol.

188

155

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Sucrose accumulation has been studied extensively in sugarcane-an example of a highly productive crop plant with the capacity for storing large quantities of sugar. Initial recognition and characterisation of the enzymes involved in sucrose synthesis and cleavage led to widely accepted models of how sucrose transport and accumulation occur. Studies on cells in culture and on isolated cellular fragments initially supported and strengthened these models but more recently have revealed weaknesses in them. Biophysical measurements and anatomical, histochemical, and tracer dye studies further eroded the older models. Molecular studies are beginning to reveal details at the gene and transcriptional levels of the enzymes involved in sucrose transport and metabolism. Collectively, results of recent research indicate the need for a new sucrose accumulation model. A dynamic model of rapid cycling and turnover of sucrose between the vacuole and metabolic and apoplastic compartments explains much of the data, but details of how the cycling is regulated remains to be discovered. *A paper presented at a symposium honouring the late John Hawker, held at the 34th meeting of the Australian Society of Plant Physiologists, Broadbeach, Queensland, September 1994.

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“…Understanding the nafure of the physiological link between phloem import and sink metabolism/compartmentation depends upon resolving tbe mechanism of phloem translocafion. If a pressure flow mechanism operates, the activities of sink metabolism/compartmentation will be the ultimate determinants of the turgor potential at the terminal end of tbe transport pathway which drives mass flow of imported assimilates (Minchin and Thorpe 1987). The cellular location and control of sink turgor will be governed by the pathway of unloading from the sieye elements and the nature of sitik metabolistn/compartmentation (Patrick 1991).…”

Section: Introductionmentioning

confidence: 99%

Turgor‐dependent unloading of photosynthates from coats of developing seed of Phaseolus vulgaris and Vicia faba. Turgor homeostasis and set points

Patrick

1994

Physiologia Plantarum

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Key physiological characteristics of turgor‐dependent efflux of photosynthates were examined using excised coats and cotyledons of developing Phaseolus vulgaris (cv. Redland Poineer) and Vicia faba (cv. Coles Prolific) seed during the linear phase of seed fill. Exposure to solutions of high osmotic potential inhibited net uptake of [14C]sucrose by cotyledons at developmental stages less than 60% of their final dry weight. The effect could not be fully reversed by transferring cotyledons to solutions set at lower osmotic potentials. The inhibition became apparent at osmotic potentials that were higher than those that caused stimulation of efflux from seed coats. Net [14C]sucrose uptake by cotyledons at more advanced stages of development was unaffected by external osmotic potential. Specified tissue layers were removed from seed coats by pretreatment with pectinase. Efflux studies with the pectinase‐modified coats of Phaseolus and Vicia seed demonstrated that the cellular site of turgordependent efflux was the ground parenchyma and thin‐wall parenchyma transfer cells, respectively. Coats subjected to long‐term (hours) incubations, under hypo‐osmotic conditions, exhibited the capacity for turgor regulation. This was mediated by turgor‐dependent efflux of solutes. The solutes exchanged were of nutritional significance to the developing embryo. The relationship between efflux and coat turgor was characterised by a turgor‐independent phase at low turgors. Once turgor exceeded a minimal value (set point), efflux increased in proportion to the magnitude of the turgor deviation (error signal) from the set point. For coats of sink‐limited seed of Vicia and Phaseolus, efflux exhibited apparent saturation at turgors above 0.25 and 0.5 MPa respectively. The putative turgor set point and slope of the turgor‐dependent component of efflux varied with seed development, the prevailing source/sink ratio and genetic differences in seed growth rate. The nature of these kinetic variations was compatible with the competitive ability of the seed. A turgor homeostat model is proposed that incorporates the observed functional attributes of turgor‐dependent efflux. Operationally, the model provides a mechanistic basis for the integration of assimilate demand by the cotyledons with assimilate import into and unloading from the seed coat.

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Is Phloem Transport Due to a Hydrostatic Pressure Gradient? Supporting Evidence From Pressure Chamber Experiments

Cited by 16 publications

References 0 publications

Vascular flows and transpiration affect peach (Prunus persica Batsch.) fruit daily growth

Vascular flows and transpiration affect peach (Prunus persica Batsch.) fruit daily growth

Temporal and Spatial Regulation of Sucrose Accumulation in the Sugarcane Stem

Turgor‐dependent unloading of photosynthates from coats of developing seed of Phaseolus vulgaris and Vicia faba. Turgor homeostasis and set points

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