Sugar unloading in roots of <i>Ricinus communis</i> L.

Chapleo, S.; Hall, J. L.

doi:10.1111/j.1469-8137.1989.tb00700.x

Cited by 11 publications

(7 citation statements)

References 22 publications

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“…For example, under conditions of active photosynthesis and assimilate transport, the proportion of sugars in it increases. Thus, a great amount of nonelectrolytes was found in the apoplast of roots and stems of various plant species [29,30,32]. Potassium partition between the cytoplasm and apoplast is also affected by tissue functional state (leaf stimulation in Mimosa pudica , for example), plant age, geotropism, source-sink state [33][34][35].…”

Section: Resultsmentioning

confidence: 99%

Potassium in the Apoplast of the Root Sink Region

Krasavina

Бурмистрова

Feshchenko

et al. 2005

Russ J Plant Physiol

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Using carboxyfluorescein, a fluorochrome transported along the phloem, we demonstrated that symplasmic phloem unloading in the watermelon root occurred in the basal zone of the meristem adjusting to the elongation zone. In the similar zones of maize and pumpkin roots, a high level of potassium was detected by X-ray microanalysis in the cell walls and intercellular spaces. Potassium concentration in these compartments comprised two-thirds of that in the cytoplasm. Such proportion between potassium concentrations in the cytoplasm and apoplast was characteristic of both the cortex and stele. Since potassium is a dominant osmotically active component in root tissues, such a proportion between its intracellular and apoplastic concentrations provides for a low turgor pressure in the cells of the sink region, in the phloem in particular. This might increase a turgor pressure gradient along the translocation route between source and sink tissues, which is a driving force for phloem assimilate transport. Key word: Zea mays -Cucurbita pepo -Cucumis melo -root apex -unloading -apoplast -X-ray microanalysisAbbreviations : CF-carboxyfluorescein; CFDA-carboxyfluorescein diacetate.

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Section: Resultsmentioning

confidence: 99%

Potassium in the Apoplast of the Root Sink Region

Krasavina

Бурмистрова

Feshchenko

et al. 2005

Russ J Plant Physiol

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“…In addition, enzymes typical of the cytosol and mitochondria (NAD^-malate dehydrogenase) or of the chloroplast (Rubiseo) were at the limit of detection. The usefulness of low speed centrifugation of whole leaves for collecting apoplastic fluid of soft leaves has also been reported by Chapleo and Hall (1989),…”

Section: Apoplastk Ph Of Sink and Source Leavesmentioning

confidence: 89%

The fate of apoplastic sucrose in sink and source leaves of Urtica dioica

Möller¹,

Beck²

1992

Physiologia Plantarum

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Experiments were performed with developing and mature leaves of Urtica dioica L. to trace differences which could be interpreted in terms of cell wall‐bound acid invertase (EC 3.2.1.26) participating in phloem unloading in a sink leaf. The pH of apoplastic fluid that was collected by gentle centrifugation of entire leaves was identical (7.1) in the two types of leaves; also, fluorometric determination with esculetin showed a neutral apoplastic pH between 7.0 in the source and 7.2 in the sink leaf. To detect whether differences in apoplastic pH occur within limited leaf areas, such as of the tissue surrounding the veins, the metabolic fate of [14C]–(fructosyl)‐sucrose that was administered via the xylem was investigated. In source leaves, there was a large transitory decrease in [14C]‐sucrose followed by a substantial resynthesis of this compound. In sink leaves, resynthesis was less significant and carbon was incorporated mainly in starch, charged soluble compounds and cell walls. However, after correction for resynthesis, the two types of leaves showed an identical capacity for sucrose cleavage. Finally, activation of the apoplastic invertase by administering labelled sucrose in buffered solution of pH 5.0 did not result in an enhanced degradation. By contrast, apoplastic fluid collected from leaves which had been infiltrated with buffer solutions of pH 5.5 and 8.0, respectively, showed a rapid adjustment of the pH close to the natural neutral value by the mesophyll tissue. The results are incompatible with the idea of an active invertase in the sink (and the source) leaves apoplast, and hence do not lend support to the theory of apoplastic cleavage of sucrose being required for phloem unloading in this kind of a utilization sink.

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“…Disc water content at full hydration was measured. The other discs were used for determination of apoplastic volume, as indicated by Tetlow and Farrar (1993), except that ''H-PEG was replaced by ''H-inulin (22 kBq ml"') according to Chapleo and Hall (1989). The MES concentration was such that the osmolarity of the solution was 620 mM, which is the global osmolarity of similar fully-hydrated leaves without their main vein, measured with a micro-osmometer (Roebling, Berlin, Germany).…”

Section: Determination Of Apoplastic Volumementioning

confidence: 99%

Phloem loading in peach: Symplastic or apoplastic?

Moing

Carbonne

Zipperlin

et al. 1997

Physiologia Plantarum

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Sorbitol and sucrose are the two main soluble carbohydrates in mature peach leaves. Both are translocated in the phloem, in peach as in other rosaceous trees. The respective role of these two soluble carbohydrates in the leaf carbon budget, and their phloem loading pathway, remain poorly documented. Though many studies have been carried out on the compartmentation and export of sucrose in sucrose-transporting species, far less is known about sorbitol in species transporting both sucrose and sorbitol. Sorbitol and sucrose concentrations were measured in several tissues and in sap, in 2-month-old peach (Prunus persica L. Batsch) seedlings, i.e. leaf blade, leaf main vein, petiole, xylem sap collected using a pressure bomb, and phloem sap collected by aphid stylets. The sorbitol to sucrose molar ratio depended on the tissue or sap, the highest value (about 7) found in the leaf main vein. Sorbitol concentration in the phloem sap was about 560 mM, whereas that of sucrose was about 140 mM. The lowest sorbitol and sucrose concentrations were observed in xylem sap collected from the shoot. The volume of the leaf apoplast, estimated by infiltration with ^H-inulin, represented about 17% ofthe leaf blade water content. This volume was used to calculate a global intracellular concentration for each carbohydrate in the leaf blade. Following these simplifying assumptions, the calculated concentration gradient between the leaf's intracellular compartment and phloem sap is nil for sorbitol and could thus allow for the sympiastic loading of the phloem of this alditol. However, infiltration of ''^C-labelled source leaves with 2 mM p-chloromercuribenzenesulfonic acid (PC-MBS), a potent inhibitor of the sucrose carrier responsible for phloem loading in sucrose-transporting plants, had a significant effect on the exudation of both labelled sucrose and sorbitol from the phloem. Therefore, in peach, which is a putative sympiastic loader according to minor vein anatomy and sorbitol concentration gradients, apoplastic loading may predominate.

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Sugar unloading in roots of Ricinus communis L.

Cited by 11 publications

References 22 publications

Potassium in the Apoplast of the Root Sink Region

Potassium in the Apoplast of the Root Sink Region

The fate of apoplastic sucrose in sink and source leaves of Urtica dioica

Phloem loading in peach: Symplastic or apoplastic?

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