Sugar Uptake and Metabolism in the Developing Endosperm of <i>Tassel-seed Tunicate</i> (<i>Ts-5 Tu</i>) Maize

Thomas, Paul A.; Felker, Frederick C.; Crawford, Cynda

doi:10.1104/pp.99.4.1540

Cited by 15 publications

(9 citation statements)

References 13 publications

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“…Similar kinetics were observed for PCMBS-sensitive sucrose uptake from the endosperm cavity of developing wheat grain by the modified 61 aleurone/sub-aleurone transfer cell complexes abutting the endosperm cavity (Wang et al 1995b). In contrast, Griffith et al (1987) found that sugar accumulation by dermal transfer cells enveloping the endosperm of developing Zea mays seed was linearly dependent upon the external sugar concentration (but see Thomas et al 1992). However, excepting the Vicia cotyledon (McDonald et al 1995 and this paper), the contribution of the transfer cells to the observed transport kinetics remains to be demonstrated.…”

Section: Discussionmentioning

confidence: 50%

“…In contrast, the kinetics of sugar uptake by the endosperm of developing embryos of Zea mays exhibited kinetics consistent with simple diffusion (Griffith et al 1987). However, this transport behaviour could be artifactual resulting from mechanical damage incurred during tissue preparation (Thomas et al 1992). Indeed, uptake of sucrose from the endosperm cavity across the plasma membranes of the modified aleurone-sub aleurone transfer cell complex appears to occur by a carriermediated and energy-dependent transport mechanism (Wang et al 1995b).…”

Section: Introductionmentioning

confidence: 90%

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Sugar uptake by the dermal transfer cells of developing cotyledons of Vicia faba L.

McDonald

Fieuw

Patrick

1996

Planta

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Abstract. Two experimental systems were developed to study the uptake of sucrose by the dermal transfer cells of developing cotyledons of Vicia faba L. First, the in-vivo state was approximated by short-term (10 min) incubation of whole cotyledons in [~4C]sucrose solutions. Under these conditions, a minimum of 67% of the ~4C label entered the dermal transfer cell complex. Of this, at least 40% crossed the plasma membranes of the epidermal transfer cells. Second, a protocol was developed to enzymatically isolate and purify dermal transfer cell protoplasts. The yields of the transfer cell protoplasts were relatively low and their preparation incurred a significant loss of plasma membrane. However, the protoplasts remained viable up to 24 h following purification and proved to be a suitable system to verify transport properties observed with whole cotyledons. Using these two experimental systems, it was established that [x4C]sucrose uptake by the dermal transfer cells exhibited features consistent with mediated energy-dependent transport. This included saturation kinetics, competition for uptake between structurally similar molecules, and inhibition of uptake by p-chloromercuribenzenesulfonic acid and several other metabolic inhibitors. For comparative purposes, sugar uptake by the storage parenchyma of the Vicia cotyledons was also examined. In contrast to the dermal transfer cell complex, sucrose uptake by the storage parenchyma displayed characteristics consistent with simple diffusion.

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Section: Discussionmentioning

confidence: 50%

Section: Introductionmentioning

confidence: 90%

Sugar uptake by the dermal transfer cells of developing cotyledons of Vicia faba L.

McDonald

Fieuw

Patrick

1996

Planta

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“…Kernel development is supported by sucrose transferred from phloem, across pedicel and basal transfer cells (Aoki et al. , 1999; Thomas et al. , 1992) to the main endosperm compartments and embryo (Shannon, 1972).…”

Section: Introductionmentioning

confidence: 99%

Positional cues for the starch/lipid balance in maize kernels and resource partitioning to the embryo

et al. 2005

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SummaryThis study tests the hypotheses that in vivo oxygen levels inside developing maize grains locally affect assimilate partitioning and ATP distribution within the kernel. These questions were addressed through combined topographical analysis (O 2 -and ATP-mapping), metabolite profiling, and isotope flux analysis. Internal and external oxygen levels were also experimentally altered. Under ambient conditions, mean O 2 concentration immediately inside starchy endosperm dropped to only 1.4% of atmospheric saturation (approximately 3.8 lM), but was 10-fold higher in the oil-storing embryo. Increasing the O 2 supply to intact kernels stimulated their O 2 demand, shifted ATP localization within the kernel, and elevated their ATP/ADP ratio. Enhanced O 2 availability also increased steady-state levels of glycolytic intermediates and those of the citric acid cycle, as well as some related pools of free amino acids. Subsequent analyses indicated that starch formation within endosperm, but not lipid biosynthesis within embryo, was adapted to the endogenous low oxygen. Increasing the O 2 supply did not change ADP-glucose levels, activity of ADP-glucose pyrophosphorylase, 13 C-labeling of ADP-glucose, or flux of 14 C-sucrose into starch. In contrast, enhanced O 2 availability increased 14 C-label uptake into the embryo, 13 C-labeling of acetyl-coenzyme A, and finally 14 C-incorporation into lipids. Lipid accumulation in embryo appeared highest in regions with higher ATP. Consistent with labeling data, a decrease in O 2 supply most strongly affected the embryo, whereas rising O 2 levels expanded ATP-rich zones toward the starch-storing endosperm and the scutellar part of embryo. The latter might be responsible for higher 14 C-label uptake into the embryo and flux toward lipid. Collectively, data indicate that the in vivo oxygen distribution in maize kernels markedly affects ATP gradients, metabolite levels, and favors assimilate partitioning toward starch within the O 2 -depleted endosperm. Clear advantages are thus evident for peripheral localization of the protein and lipid storing structures in maize kernels.

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“…In vitro studies of sugar influx by exposed endosperm of developing maize kernels suggested that sugar influx occurred by passive diffusion alone (Griffith et al 1987). However, this behaviour could result from mechanical damage to the uptake mechanism (Felker et al 1990; Thomas et al 1992). The developing wheat grain appears to be a more robust experimental model.…”

Section: Filial Transport Mechanismsmentioning

confidence: 99%

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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Sugar Uptake and Metabolism in the Developing Endosperm of Tassel-seed Tunicate (Ts-5 Tu) Maize

Cited by 15 publications

References 13 publications

Sugar uptake by the dermal transfer cells of developing cotyledons of Vicia faba L.

Sugar uptake by the dermal transfer cells of developing cotyledons of Vicia faba L.

Positional cues for the starch/lipid balance in maize kernels and resource partitioning to the embryo

Post-Sieve Element Transport of Sucrose in Developing Seeds

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