Abstract
Abstract As reported in a previous paper ( Plant, Cell and Environment 24, 357–365, 2001), introduction of sucrose phosphorylase into the cytosol of potato results in increased respiration, an inhibition of starch accumulation and decreased tuber yield. Herein a more detailed investigation into the effect of sucrose phosphorylase expression on tuber metabolism, in order to understand why storage and growth are impaired is described. (1) Although the activity of the introduced sucrose phosphorylase was low and accounted for less than 10% of that of sucrose synthase its expression led to a decrease in the activities of enzymes of starch synthesis relative to enzymes of glycolysis and relative to total amylolytic activity. (2) Incubation of tuber discs in [ 14 C]glucose revealed that the transformants display a two‐fold increase of the unidirectional rate of sucrose breakdown. However this was largely compensated by a large stimulation of sucrose re‐synthesis and therefore the net rate of sucrose breakdown was not greatly affected. Despite this fact major shifts in tuber metabolism, including depletion of sucrose to very low levels, higher rates of glycolysis, and larger pools of amino acids were observed in these lines. (3) Expression of sucrose phosphorylase led to a decrease of the cellular ATP/ADP ratio and energy charge in intact growing tubers. It was estimated that at least 30% of the ATP formed during respiration is consumed as a result of the large acceleration of the cycle of sucrose breakdown and re‐synthesis in the transformants. Although the absolute rate of starch synthesis in short‐term labelling experiments with discs rose, starch synthesis fell relative to other fluxes including respiration, and the overall starch content of the tubers was lower than in wild‐type tubers. (4) External supply of amino acids to replace sucrose as an osmoticum led to a feed‐back inhibition of glycolysis, but did not restore allocation to starch. (5) However, an external supply of the non‐metabolizable sucrose analogue palatinose – but not sucrose itself – stimulated flux to starch in the transformants. (6) The results indicate that the impaired performance of sucrose phosphorylase‐expressing tubers is attributable to decreased levels of sucrose and increased energy consumption during sucrose futile cycling, and imply that sucrose degradation via sucrose synthase is important to maintain a relatively large sucrose pool and to minimize the ATP consumption required for normal metabolic function in the wild type.
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Claims 18
Claim · model-written summary
Sucrose phosphorylase activity was less than one tenth of sucrose synthase activity.
- Taxon
- potato
Solanum tuberosumt0 - Outcome
- activity of the introduced sucrose phosphorylasee0
- Value
- less than 10%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the activity of the introduced sucrose phosphorylase was low and accounted for less than 10% of that of sucrose synthase”
t0“potato tubers”
Claim · model-written summary
Expression decreased starch synthesis enzyme activities relative to glycolytic enzymes and amylolytic activity.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- its expressione0
- Outcome
- activities of enzymes of starch synthesise0
- Direction
- decreasee0
- Comparator
- enzymes of glycolysise0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“its expression led to a decrease in the activities of enzymes of starch synthesis relative to enzymes of glycolysis and relative to total amylolytic activity”
t0“potato tubers”
Claim · model-written summary
Transformants had twice the unidirectional sucrose breakdown rate.
- Taxon
- potatoSolanum tuberosumt0
- Material
- transformantse0
- Outcome
- unidirectional rate of sucrose breakdowne0
- Direction
- increasee0
- Value
- two‐folde0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the transformants display a two‐fold increase of the unidirectional rate of sucrose breakdown”
t0“potato tubers”
Claim · model-written summary
Sucrose resynthesis was strongly stimulated.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- sucrose re‐synthesise0
- Direction
- stimulatione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this was largely compensated by a large stimulation of sucrose re‐synthesis”
t0“potato tubers”
Claim · model-written summary
Net sucrose breakdown changed little.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- net rate of sucrose breakdowne0
- Direction
- not greatly affectede0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the net rate of sucrose breakdown was not greatly affected”
t0“potato tubers”
Claim · model-written summary
Sucrose in the tubers was depleted.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- sucrosee0
- Direction
- depletione0
- Qualifier
- very low levelse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“depletion of sucrose to very low levels”
t0“potato tubers”
Claim · model-written summary
Glycolysis rates were higher in the transformants.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- rates of glycolysise0
- Direction
- highere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“higher rates of glycolysis”
t0“potato tubers”
Claim · model-written summary
Amino acid pools were larger in the transformants.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- pools of amino acidse0
- Direction
- largere0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“larger pools of amino acids”
t0“potato tubers”
Claim · model-written summary
Expression decreased tuber ATP/ADP ratio and energy charge.
- Taxon
- potatoSolanum tuberosumt0
- Organ / stage
- intact growing tuberse0
- Treatment
- Expression of sucrose phosphorylasee0
- Outcome
- cellular ATP/ADP ratio and energy chargee0
- Direction
- decreasee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Expression of sucrose phosphorylase led to a decrease of the cellular ATP/ADP ratio and energy charge in intact growing tubers”
t0“potato tubers”
Claim · model-written summary
At least 30% of respiratory ATP was estimated to be consumed by accelerated sucrose cycling.
- Taxon
- potatoSolanum tuberosumt0
- Material
- transformantse0
- Outcome
- ATP formed during respiratione0
- Value
- at least 30%e0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“at least 30% of the ATP formed during respiration is consumed as a result of the large acceleration of the cycle of sucrose breakdown and re‐synthesis in the transformants”
t0“potato tubers”
Claim · model-written summary
Absolute starch synthesis rose in short-term disc labeling.
- Taxon
- potatoSolanum tuberosumt0
- Organ / stage
- discse0
- Outcome
- absolute rate of starch synthesise0
- Direction
- rosee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“absolute rate of starch synthesis in short‐term labelling experiments with discs rose”
t0“potato tubers”
Claim · model-written summary
Starch synthesis fell relative to other fluxes.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- starch synthesise0
- Direction
- felle0
- Comparator
- other fluxes including respiratione0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“starch synthesis fell relative to other fluxes including respiration”
t0“potato tubers”
Claim · model-written summary
Tuber starch content was lower than in wild type.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- overall starch contente0
- Direction
- lowere0
- Comparator
- wild‐type tuberse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“overall starch content of the tubers was lower than in wild‐type tubers”
t0“potato tubers”
Claim · model-written summary
External amino acids inhibited glycolysis.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- External supply of amino acidse0
- Outcome
- glycolysise0
- Direction
- inhibitione0
- Comparator
- sucrosee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“External supply of amino acids to replace sucrose as an osmoticum led to a feed‐back inhibition of glycolysis”
t0“potato tubers”
Claim · model-written summary
External amino acids did not restore allocation to starch.
- Taxon
- potatoSolanum tuberosumt0
- Treatment
- External supply of amino acidse1
- Outcome
- allocation to starche0
- Direction
- did not restoree0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“but did not restore allocation to starch”
t0“potato tubers”
e1“External supply of amino acids to replace sucrose as an osmoticum led to a feed‐back inhibition of glycolysis”
Claim · model-written summary
Palatinose stimulated flux to starch in transformants.
- Taxon
- potatoSolanum tuberosumt0
- Material
- transformantse0
- Treatment
- palatinosee0
- Outcome
- flux to starche0
- Direction
- stimulatede0
- Comparator
- sucrose itselfe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“an external supply of the non‐metabolizable sucrose analogue palatinose – but not sucrose itself – stimulated flux to starch in the transformants”
t0“potato tubers”
Claim · model-written summary
Lower sucrose and greater energy use during sucrose cycling explain poor tuber performance.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- impaired performancee0
- Qualifier
- decreased levels of sucrose and increased energy consumption during sucrose futile cyclinge0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the impaired performance of sucrose phosphorylase‐expressing tubers is attributable to decreased levels of sucrose and increased energy consumption during sucrose futile cycling”
t0“potato tubers”
Claim · model-written summary
Sucrose synthase degradation helps maintain the sucrose pool and limit ATP consumption.
- Taxon
- potatoSolanum tuberosumt0
- Outcome
- normal metabolic functione0
- Qualifier
- sucrose degradation via sucrose synthasee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“sucrose degradation via sucrose synthase is important to maintain a relatively large sucrose pool and to minimize the ATP consumption required for normal metabolic function in the wild type”
t0“potato tubers”
The same questions in other papers
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See all 10 papers →Claims are grouped by organism, treatment and what was measured or targeted. A paper counts as positive when any of its claims in the group is positive.