Abstract
The proton-sucrose symporter mediates the key transport step in the resource distribution system that allows many plants to function as multicellular organisms. In the results reported here, we identify sucrose as a signaling molecule in a previously undescribed signal-transduction pathway that regulates the symporter. Sucrose symporter activity declined in plasma membrane vesicles isolated from leaves fed exogenous sucrose via the xylem transpiration stream. Symporter activity dropped to 35-50% of water controls when the leaves were fed 100 mM sucrose and to 20-25% of controls with 250 mM sucrose. In contrast, alanine symporter and glucose transporter activities did not change in response to sucrose treatments. Decreased sucrose symporter activity was detectable after 8 h and reached a maximum by 24 h. Kinetic analysis of transport activity showed a decrease in Vmax. RNA gel blot analysis revealed a decrease in symporter message levels, suggesting a drop in transcriptional activity or a decrease in mRNA stability. Control experiments showed that these responses were not the result of changing osmotic conditions. Equal molar concentrations of hexoses did not elicit the response, and mannoheptulose, a hexokinase inhibitor, did not block the sucrose effect. These data are consistent with a sucrose-specific response pathway that is not mediated by hexokinase as the sugar sensor. Sucrose-dependent changes in the sucrose symporter were reversible, suggesting this sucrose-sensing pathway can modulate transport activity as a function of changing sucrose concentrations in the leaf. These results demonstrate the existence of a signaling pathway that can control assimilate partitioning at the level of phloem translocation.
Abstract from the paper’s OpenAlex record, shown for indexing and research. Copyright remains with the authors or the publisher. Read at the source ↗
The text the model read, with the source record’s inline markup (italics, sub- and superscripts) rendered and its character entities decoded; quote offsets refer to the raw text.
Claims 13
Claim · model-written summary
Feeding leaves 100 mM sucrose lowered symporter activity to 35-50% of water controls.
Verbatim
e0“Symporter activity dropped to 35-50% of water controls when the leaves were fed 100 mM sucrose”
Claim · model-written summary
Feeding leaves 250 mM sucrose lowered symporter activity to 20-25% of controls.
Verbatim
e0“Symporter activity dropped to 35-50% of water controls when the leaves were fed 100 mM sucrose and to 20-25% of controls with 250 mM sucrose”
Claim · model-written summary
Alanine symporter activity did not change with sucrose treatment.
Not reportedTaxonComparator
Verbatim
e0“alanine symporter and glucose transporter activities did not change in response to sucrose treatments”
Claim · model-written summary
Glucose transporter activity did not change with sucrose treatment.
Not reportedTaxonComparator
Verbatim
e0“alanine symporter and glucose transporter activities did not change in response to sucrose treatments”
Claim · model-written summary
Decreased sucrose symporter activity was detectable after 8 h.
Not reportedTaxon
Verbatim
e0“Decreased sucrose symporter activity was detectable after 8 h”
Claim · model-written summary
The sucrose symporter activity decline reached a maximum by 24 h.
Not reportedTaxon
Verbatim
e0“Decreased sucrose symporter activity was detectable after 8 h and reached a maximum by 24 h”
Claim · model-written summary
Transport kinetic analysis showed a decrease in Vmax.
Not reportedTaxon
Verbatim
e0“Kinetic analysis of transport activity showed a decrease in Vmax”
Claim · model-written summary
Symporter message levels decreased.
Not reportedTaxon
Verbatim
e0“RNA gel blot analysis revealed a decrease in symporter message levels”
Claim · model-written summary
Changing osmotic conditions did not account for the sucrose responses.
- Outcome
- not the result of changing osmotic conditionse0
Not reportedTaxon
Verbatim
e0“these responses were not the result of changing osmotic conditions”
Claim · model-written summary
Equal molar concentrations of hexoses did not elicit the sucrose response.
Not reportedTaxonComparator
Verbatim
e0“Equal molar concentrations of hexoses did not elicit the response”
Claim · model-written summary
Mannoheptulose did not block the sucrose effect.
Not reportedTaxonComparator
Verbatim
e0“mannoheptulose, a hexokinase inhibitor, did not block the sucrose effect”
Claim · model-written summary
Sucrose-dependent symporter changes were reversible.
- Outcome
- changes in the sucrose symporter were reversiblee0
Not reportedTaxon
Verbatim
e0“Sucrose-dependent changes in the sucrose symporter were reversible”
Claim · model-written summary
Sucrose acts as a signal in a pathway regulating the symporter and assimilate partitioning.
Not reportedTaxon
Verbatim
e0“we identify sucrose as a signaling molecule in a previously undescribed signal-transduction pathway that regulates the symporter”
e1“a signaling pathway that can control assimilate partitioning at the level of phloem translocation”