Structural and Physiological Changes in Sugar Beet Leaves during Sink to Source Conversion

Fellows, Robert J.; Geiger, Donald R.

doi:10.1104/pp.54.6.877

Cited by 136 publications

(85 citation statements)

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“…This change is paralleled by the development of sucrose phosphate synthase activity rather than by a decrease of the sucrose-hydrolyzing enzymes (12). In the same material, phloem loading begins 35 to 45 h prior to onset of export, and it has been suggested that this triggers the initiation of export by increasing sufficiently the solute concentration within the conducting cells (7).…”

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confidence: 87%

“…Apart from its central role in leaf development, this transition provides a straightforward system to compare sink and source tissue without dealing with the complications introduced by the study of different organs (27). The sink/source transition of the leaf is a highly integrated process beginning when the leaf has reached about 35% final lamina length, and proceeds from the tip to the base (7). The transition is made possible by a series of changes affecting both metabolism and transport.…”

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confidence: 99%

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Plasma Membrane Vesicles from Source and Sink Leaves

Lemoine¹,

Gallet²,

Gaillard³

et al. 1992

Plant Physiol.

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Plasma membrane vesicles (PMVs) were prepared by phase partitioning from microsomal fractions of either sink or source leaves of sugar beet (Beta vulgaris L.). The purity, the internal volume, the sidedness, and the sealingness of PMVs prepared from sink leaves did not differ from those measured with PMVs from source leaves. Yet, in response to an imposed proton motive force, PMVs from source leaves accumulated about 4-fold more sucrose than PMVs from sink leaves. The developmental stage did not affect the uptake of glucose and valine in PMVs prepared from leaf tissues. It was concluded that the sink/source transition is accompanied either by the incorporation into the plasma membrane of leaf cells of proteins mediating proton-sucrose cotransport, or by their activation. N-ethylmaleimide and a polyclonal ascitic fluid directed against the 42-kD region of the plasma membrane containing a putative sucrose carrier inhibited the uptake of sucrose in PMVs from source leaves, but not in PMVs from sink leaves. Sodium dodecyl sulfate gel electrophoresis and western blot suggested that the 42 polypeptide was more abundant in the PMVs from source leaves than in the PMVs from sink leaves.

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confidence: 87%

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confidence: 99%

Plasma Membrane Vesicles from Source and Sink Leaves

Lemoine¹,

Gallet²,

Gaillard³

et al. 1992

Plant Physiol.

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“…Discs were also obtained from young sink leaves (3-4 cm in length) in which the lower portion of the leaf lamina was still unrolled. Previous studies (9,17) …”

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confidence: 99%

Sucrose Hydrolysis in Relation to Phloem Translocation in Beta vulgaris

Giaquinta

1977

Plant Physiol.

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Asymmetically labeled sucrose, 14C(fructosyl)sucrose, was used to determine whether sucrose undergoes extracellar hydrolysis duing phloem trandocation in the sugar beet, Beta vulgaris. In addition, the metabolsm of variom sugars accmulated and trasocated was determined in varios gions of the plant. These proceses were studied in detached regions as well as in the intact, trnlocating plant in the source leaf, along the trslocation path, and in a rapidly growing sink leaf nd storage beet. Tbe data show that, unlike sucrose accumulation into the sink tisse of sugarcane, ucrose is neither hydrolzyed prior to phloem loading or during tansit, nor is it extrcellularty hydrolyzed during accumulation into sink leaves or the storage beet.Although it is well established that photosynthetically derived assimilates are transported between source and sink regions along a gradient of hydrostatic pressure, relatively little is known about the cellular and metabolic correlates of the translocation process. The translocation system is generally divided into three structurally and physiologically distinct regions: the source, path, and sink regions. Recent structural and physiological studies (5,10,17,18) have indicated that the path region is relatively passive in the translocation process, in that the driving force for transport resides in metabolism-dependent processes operating in the source and sink regions.From a mechanistic viewpoint, the major emphasis in the phloem transport literature has been toward elucidating the role of the path at the expense of source and sink metabolism, particularly at the cellular level. Recent studies by Geiger and co-workers (12, 13) have investigated events operating in the source leaf of Beta vulgaris during the loading of sucrose into the phloem prior to translocation. What has emerged from these studies and from the more recent studies by Giaquinta (14,15 (19).Hydrolysis of sucrose to hexoses by a free space invertase prior to accumulation quite convincingly occurs in sugarcane tissue. The paucity of information on this subject in other species makes it difficult to determine whether these events constitute a general mechanism of sink metabolism of translocate or whether they are characteristic for the sugarcane system.The literature on the role of extracellular invertase in phloem translocation in both source and sink regions is controversial. Part of the discrepancy and variability probably arises from the observation that invertase activity can be induced in some tissues by physical dissection or prolonged washing (8). Another possibility is that extracellular invertase as related to translocation is not universally present in various species and that sucrose need not be extracellularly hydrolyzed prior to membrane transport into the sink tissue.The form in which sucrose is transported across cell membranes during phloem translocation is important in elucidating the nature and selectivity of membrane carriers involved in phloem loading and unloading of sugars in the source and s...

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“…For most plants, this occurs by loading Suc into the phloem and transporting it from source tissues (net exporters) to sink tissues (net importers), where Suc is unloaded (Turgeon, 1989;van Bel, 2003). This process is well characterized at the physiological, biochemical, and anatomical levels (Hofstra and Nelson, 1969;Fellows and Geiger, 1974;Evert et al, 1978;Nguyen-Quoc et al, 1990;Huber and Hanson, 1992;Evert et al, 1996a;Koch, 1996;Paul and Foyer, 2001). However, despite the obvious importance of this process for plant growth and development, few genes that function in carbon partitioning have been identified.…”

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confidence: 99%