Abstract
The two genes encoding sucrose synthase in maize (Sh1 and Sus1) show markedly different responses to changes in tissue carbohydrate status. This enzyme is widely regarded as pivotal to sucrose partitioning, import, and/or metabolism by developing plant organs. Excised maize root tips were incubated for varying periods in different sugars and a range of concentrations. The Sh1 mRNA was maximally expressed under conditions of limited carbohydrate supply (~0.2% glucose). In contrast, Sus1 transcript levels were low or nondetectable under sugar-depleted conditions and peaked at 10-fold greater glucose concentrations (2.0%). Responses to other metabolizable sugars were similar, but L-glucose and elevation of osmolarity with mannitol had little effect. Plentiful sugar supplies thus increased expression of Sus1, whereas reduced sugar availability enhanced Sh1. At the protein level, shifts in abundance of subunits encoded by Sh1 and Sus1 were much less pronounced but corresponded to changes in respective mRNA levels. Although total enzyme activity did not show net change, cellular localization of sucrose synthase protein was markedly altered. In intact roots, sucrose synthase was most prevalent in the stele and apex. In contrast, sugar depletion favored accumulation in peripheral cells, whereas high sugar levels resulted in elevated expression in all cell types. The differential response of the two sucrose synthase genes to sugars provides a potential mechanism for altering the pattern of enzyme distribution in response to changing carbohydrate status and also for adjusting the sucrose-metabolizing capacity of importing cells relative to levels of available photosynthetic products.
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Claims 14
Claim · model-written summary
Sh1 mRNA expression was maximal at limited carbohydrate supply of about 0.2% glucose.
- Treatment
- limited carbohydrate supply (~0.2% glucose)e0
- Gene
- Sh1e0
- Outcome
- mRNAe0
- Direction
- maximally expressede0
Zea maysNot reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The Sh1 mRNA was maximally expressed under conditions of limited carbohydrate supply (~0.2% glucose).”
t0“Maize”
Claim · model-written summary
Sus1 transcripts were low or undetectable under sugar depletion.
- Treatment
- sugar-depleted conditionse0
- Gene
- Sus1e0
- Outcome
- transcript levelse0
- Direction
- low or nondetectablee0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Sus1 transcript levels were low or nondetectable under sugar-depleted conditions”
t0“Maize”
Claim · model-written summary
Sus1 transcripts peaked at 2.0% glucose, ten times the Sh1 peak concentration.
- Treatment
- glucose concentrations (2.0%)e0
- Gene
- Sus1e1
- Outcome
- transcript levelse1
- Direction
- peakede0
- Value
- 2.0%e0
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“peaked at 10-fold greater glucose concentrations (2.0%).”
e1“Sus1 transcript levels were low or nondetectable under sugar-depleted conditions”
t0“Maize”
Claim · model-written summary
Other metabolizable sugars produced similar maize root responses.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Responses to other metabolizable sugars were similar”
t0“Maize”
Claim · model-written summary
L-glucose had little effect on maize root sucrose synthase responses.
Not reportedComparatorOutcome
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“L-glucose and elevation of osmolarity with mannitol had little effect.”
t0“Maize”
Claim · model-written summary
Mannitol-induced osmolarity elevation had little effect on maize root sucrose synthase responses.
Not reportedComparatorOutcome
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“L-glucose and elevation of osmolarity with mannitol had little effect.”
t0“Maize”
Claim · model-written summary
Plentiful sugar increased Sus1 expression.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Plentiful sugar supplies thus increased expression of Sus1”
t0“Maize”
Claim · model-written summary
Reduced sugar availability enhanced Sh1 expression.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“reduced sugar availability enhanced Sh1”
t0“Maize”
Claim · model-written summary
Sh1 and Sus1 protein subunit abundance shifted less than mRNA but in corresponding directions.
Not reportedTaxon
Verbatim
e0“At the protein level, shifts in abundance of subunits encoded by Sh1 and Sus1 were much less pronounced but corresponded to changes in respective mRNA levels.”
Claim · model-written summary
Total sucrose synthase enzyme activity showed no net change.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Although total enzyme activity did not show net change”
t0“Maize”
Claim · model-written summary
Sucrose synthase protein localization changed markedly with sugar status.
Not reportedTreatmentComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“cellular localization of sucrose synthase protein was markedly altered.”
t0“Maize”
Claim · model-written summary
In intact roots, sucrose synthase was most prevalent in the stele and apex.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“In intact roots, sucrose synthase was most prevalent in the stele and apex.”
t0“Maize”
Claim · model-written summary
Sugar depletion favored sucrose synthase accumulation in peripheral root cells.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“sugar depletion favored accumulation in peripheral cells”
t0“Maize”
Claim · model-written summary
High sugar raised sucrose synthase expression in all cell types.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“high sugar levels resulted in elevated expression in all cell types.”
t0“Maize”
The same questions in other papers
glucose · molecular: expression · Zea mays (maize)Positive and negative results
1 paper in the same direction as this paper · 1 in the opposite direction · 1 reporting no difference from an alternative
- positive
- no effect
- no effect
carbohydrate · molecular: expression · Zea mays (maize)Results agree
1 paper in the same direction as this paper
- positive
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.