Update on sucrose transport in higher plants

Kühn, Christina; Barker, Laurence; Bürkle, Lukas; Frommer, W. B.

doi:10.1093/jxb/50.special_issue.935

Cited by 83 publications

(24 citation statements)

References 151 publications

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“…It is also unlikely that trehalose impairs phloem transport by inhibiting the activity of the Suc transporter. A decreased phloem transport would have resulted in the accumulation of soluble sugars (Kü hn et al, 1999) that was, however, not the case (Fig. 3).…”

Section: Trehalose Alters the Shoot-root Allocation Of Carbonmentioning

confidence: 91%

Trehalose Induces the ADP-Glucose Pyrophosphorylase Gene,ApL3, and Starch Synthesis in Arabidopsis

et al. 2000

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In Arabidopsis, genes encoding functional enzymes for the synthesis and degradation of trehalose have been detected recently. In this study we analyzed how trehalose affects the metabolism and development of Arabidopsis seedlings. Exogenously applied trehalose (25 mm) strongly reduced the elongation of the roots and, concomitantly, induced a strong accumulation of starch in the shoots, whereas the contents of soluble sugars were not increased. When Arabidopsis seedlings were grown on trehalose plus sucrose (Suc), root elongation was restored, but starch still accumulated to a much larger extent than during growth on Suc alone. The accumulation of starch in the shoots of trehalose-treated seedlings was accompanied by an increased activity of ADP-glucose pyrophosphorylase and an induction of the expression of the ADP-glucose pyrophosphorylase gene, ApL3. Even in the presence of 50 mm Suc, which itself also slightly induced ApL3, trehalose (5 mm) led to a further increase in ApL3 expression. These results suggest that trehalose interferes with carbon allocation to the sink tissues by inducing starch synthesis in the source tissues. Furthermore, trehalose induced the expression of the ␤-amylase gene, AT-␤-Amy, in combination with Suc but not when trehalose was supplied alone, indicating that trehalose can modulate sugar-mediated gene expression.

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Section: Trehalose Alters the Shoot-root Allocation Of Carbonmentioning

confidence: 91%

Trehalose Induces the ADP-Glucose Pyrophosphorylase Gene,ApL3, and Starch Synthesis in Arabidopsis

et al. 2000

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“…For phloem translocation, the net products of the Calvin cycle are converted into sucrose which is thought to constitute the main metabolic sink for organic C generated during photosynthesis (Martin et al, 1993 [13] ). In most plant species, sucrose is the major transport form of reduced C for long distance transport (Kühn et al, 1999 [12] ). According to a calculation by Peuke (2000 [18] ), about one third of the photo-assimilates of herbaceous plants are exported to the roots, mainly in the form of sucrose; even higher values (up to 70 % of the assimilated C) were observed to be transported under nutrient shortage due to enhanced root growth (Peuke, 2000 [18] ).…”

Section: Introductionmentioning

confidence: 99%

Assimilate Transport in the Xylem Sap of Pedunculate Oak (Quercus robur) Saplings

et al. 2001

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The rates of photosynthesis and transpiration, as well as the concentrations of organic compounds (total soluble non‐protein N compounds [TSNN], soluble carbohydrates), in the xylem sap were determined during two growth seasons in one‐year‐old Quercus robur saplings. From the data, the total C gain of the leaves, by both photosynthesis and the transpiration stream, was calculated. Large amounts of C were allocated to the leaves by the transpiration stream; depending on the time of day and the environmental conditions the portion of C originating from xylem transport amounted to 8 to 91% of total C delivery to the leaves. Particularly under conditions of reduced photosynthesis, e.g., during midday depression of photosynthesis, a high percentage of the total C delivery was provided to the leaves by the transpiration stream (83 to 91 %). Apparently, attack by phloem‐feeding aphids lowered the assimilate transport from roots to shoots; as a consequence the portion of C available to the leaves from xylem transport amounted to only 12 to 16 %. The most abundant organic compounds transported in the xylem sap were sugars (sucrose, glucose, fructose) with concentrations of ca. 50 to 500 μmol C ml‐1, whereas C from N compounds was of minor significance (3 to 20 μmol ml‐1 C). The results indicate a significant cycling of C in the plants because the daily transport of C with the transpiration stream exceeded the daily photosynthetic CO2 fixation in several cases. This cycling pool of C may sustain delivery of photosynthate to heterotrophic tissues, independent of short time fluctuations in photosynthetic CO2 fixation.

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“…Positive pressure in the leaf phloem results from hyperaccumulation of an osmotically active solute. In most plants this solute is sucrose, which is loaded into the phloem by an electrogenic secondary active proton-sucrose symporter (3)(4)(5). Recently, the sucrose transport activity of a sugar beet leaf proton-sucrose symporter (BvSUT1) was found to be negatively regulated by sucrose and not by hexoses or changes in osmotic potential (6), but the mechanism and implications of this regulatory pathway remained unresolved.…”

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confidence: 99%

Sucrose-mediated transcriptional regulation of sucrose symporter activity in the phloem

Vaughn

Harrington

Bush

2002

Proc. Natl. Acad. Sci. U.S.A.

193

165

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A proton-sucrose symporter mediates the key step in carbon export from leaves of most plants. Sucrose transport activity and steady-state mRNA levels of BvSUT1, a sugar beet leaf sucrose symporter, are negatively regulated specifically by sucrose. Results reported here show that BvSUT1 mRNA was localized to companion cells of the leaf's vascular system, which supports its role in the systemic distribution of photoassimilate. Immunoblot analysis showed that decreased transport activity was caused by a reduction in the abundance of symporter protein. RNA gel blot analysis of the leaf symporter revealed that message levels also declined, and nuclear run-on experiments demonstrated that this was the result of decreased transcription. Further analysis showed that symporter protein and message are both degraded rapidly. Taken together, these data show that phloem loading is regulated by means of sucrose-mediated changes in transcription of a phloemspecific sucrose symporter gene in a regulatory system that may play a pivotal role in balancing photosynthetic activity with resource utilization. P lants are photoautotrophic organisms composed of both heterotrophic (sink) and autotrophic (source) tissues. Resources acquired via photosynthesis in source leaves are loaded into the phloem of the plant's elaborate vascular system and distributed among the sink tissues in a process called ''assimilate partitioning''. Because up to 80% of all fixed carbon is exported to sinks (1), regulation of assimilate partitioning is vital to plant growth and development, and it can have dramatic affects on crop yield and productivity (2). Long-distance transport in the phloem cells of the plant vascular system is mediated by a positive hydrostatic pressure difference between the source and sink tissues that drives mass flow of solution. Positive pressure in the leaf phloem results from hyperaccumulation of an osmotically active solute. In most plants this solute is sucrose, which is loaded into the phloem by an electrogenic secondary active proton-sucrose symporter (3-5). Recently, the sucrose transport activity of a sugar beet leaf proton-sucrose symporter (BvSUT1) was found to be negatively regulated by sucrose and not by hexoses or changes in osmotic potential (6), but the mechanism and implications of this regulatory pathway remained unresolved. Here we report that sucrose transport activity in the phloem is regulated via sucrose-mediated changes in transcription of the proton-sucrose symporter gene in a regulatory system that plays a pivotal role in balancing photosynthetic activity with resource utilization. Materials and MethodsTissue Fixation and Embedding. Leaf tissue from mature sugar beets (Beta vulgaris Linnaeus) was fixed on ice for 6 h under vacuum in 4% wt/vol paraformaldehyde in potassium phosphate buffer (pH 7.4). Tissue was dehydrated through a 10% stepgraded ethanol series beginning at 20% and ending at 90% and allowed to incubate overnight at 4°C. After three 100% ethanol washes, the tissue was substituted with tertiary...

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Update on sucrose transport in higher plants

Cited by 83 publications

References 151 publications

Trehalose Induces the ADP-Glucose Pyrophosphorylase Gene,ApL3, and Starch Synthesis in Arabidopsis

Trehalose Induces the ADP-Glucose Pyrophosphorylase Gene,ApL3, and Starch Synthesis in Arabidopsis

Assimilate Transport in the Xylem Sap of Pedunculate Oak (Quercus robur) Saplings

Sucrose-mediated transcriptional regulation of sucrose symporter activity in the phloem

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