Abstract
The time course of loss of14C from H14CO3-labelled carrot tissue has been measured. The graph of log (14C remaining in the cells) versus time can be fitted by two exponential components. The graph of log (rate of 14C loss over successive periods) versus time can also be fitted by two exponential components using the same fitting procedure. However, the half times of the components fitting the two types of graph are not the same, and therefore the apparently good fit is not valid. Three exponential components can be fitted to the two types of plot such that their rate constants are equal and their intercepts in the correct theoretical relationship. Their rate constants are about 7 h−1, 1.5 h−1, and less than 0.1 h−1, and they probably correspond to the total HCO3−-CO2 in the cell, the malate in the cytoplasm, and the malate in the vacuole, respectively. From these data it is shown that one can calculate the influx of HCO3−-CO2 across the plasmalemma, and the influx of malate across the tonoplast during accumulation of endogenously produced malate. The time course of uptake of 14C-malate is estimated as the sum of 14C accumulated in the tissue and 14C evolved as CO2. At 1 mM external malate total uptake is linear with time, suggesting that uptake is limited by and equal to the influx across the plasmalemma. At higher external malate concentrations the evolution of 14CO2 saturates but accumulation in the tissue continues to rise. Under these conditions it is concluded that the tonoplast influx of malate can be calculated and that this influx does not saturate at high external malate concentrations. The net efflux of malate is very small but measurable. The efflux of 14C-labelled malate is not stimulated by external malate−, Cl−, NO3− or SO4−. There are therefore no plasmalemma systems exchanging internal malate for these anions.
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Claims 15
Claim · model-written summary
Two-exponential fits to the two radiocarbon-loss plots gave inconsistent half times and were judged invalid.
- Taxon
- carrot
Daucus carotat0 - Outcome
- apparently good fit is not valide0
- Comparator
- two types of graphe0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“the half times of the components fitting the two types of graph are not the same, and therefore the apparently good fit is not valid”
t0“Carrot”
Claim · model-written summary
A three-component model fit both radiocarbon-loss plots with equal rate constants and theoretically related intercepts.
- Taxon
- carrotDaucus carotat0
- Outcome
- Three exponential components can be fitted to the two types of plote0
- Value
- Three exponential componentse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Three exponential components can be fitted to the two types of plot such that their rate constants are equal and their intercepts in the correct theoretical relationship”
t0“Carrot”
Claim · model-written summary
The first fitted rate constant was about 7 h−1 and was attributed to cellular bicarbonate and carbon dioxide.
- Taxon
- carrotDaucus carotat0
- Outcome
- rate constantse0
- Value
- 7 h−1e0
- Qualifier
- probably correspond to the total HCO3−-CO2 in the celle0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Their rate constants are about 7 h−1, 1.5 h−1, and less than 0.1 h−1, and they probably correspond to the total HCO3−-CO2 in the cell, the malate in the cytoplasm, and the malate in the vacuole, respectively”
t0“Carrot”
Claim · model-written summary
The second fitted rate constant was 1.5 h−1 and was attributed to cytoplasmic malate.
- Taxon
- carrotDaucus carotat0
- Outcome
- rate constantse0
- Value
- 1.5 h−1e0
- Qualifier
- the malate in the cytoplasme0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Their rate constants are about 7 h−1, 1.5 h−1, and less than 0.1 h−1, and they probably correspond to the total HCO3−-CO2 in the cell, the malate in the cytoplasm, and the malate in the vacuole, respectively”
t0“Carrot”
Claim · model-written summary
The third fitted rate constant was below 0.1 h−1 and was attributed to vacuolar malate.
- Taxon
- carrotDaucus carotat0
- Outcome
- rate constantse0
- Value
- less than 0.1 h−1e0
- Qualifier
- the malate in the vacuolee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“Their rate constants are about 7 h−1, 1.5 h−1, and less than 0.1 h−1, and they probably correspond to the total HCO3−-CO2 in the cell, the malate in the cytoplasm, and the malate in the vacuole, respectively”
t0“Carrot”
Claim · model-written summary
The radiocarbon-loss data permit calculation of bicarbonate and carbon dioxide influx across the plasmalemma.
- Taxon
- carrotDaucus carotat0
- Outcome
- influx of HCO3−-CO2 across the plasmalemmae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“one can calculate the influx of HCO3−-CO2 across the plasmalemma, and the influx of malate across the tonoplast during accumulation of endogenously produced malate”
t0“Carrot”
Claim · model-written summary
The data permit calculation of malate influx across the tonoplast during accumulation of endogenous malate.
- Taxon
- carrotDaucus carotat0
- Outcome
- influx of malate across the tonoplaste0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“one can calculate the influx of HCO3−-CO2 across the plasmalemma, and the influx of malate across the tonoplast during accumulation of endogenously produced malate”
t0“Carrot”
Claim · model-written summary
At 1 mM external malate, carrot tissue uptake was linear over time.
- Taxon
- carrotDaucus carotat0
- Treatment
- 1 mM external malatee0
- Outcome
- total uptake is linear with timee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At 1 mM external malate total uptake is linear with time”
t0“Carrot”
Claim · model-written summary
At 1 mM external malate, uptake appeared limited by and equal to plasmalemma influx.
- Taxon
- carrotDaucus carotat0
- Treatment
- 1 mM external malatee0
- Outcome
- uptake is limited by and equal to the influx across the plasmalemmae0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At 1 mM external malate total uptake is linear with time, suggesting that uptake is limited by and equal to the influx across the plasmalemma”
t0“Carrot”
Claim · model-written summary
At higher external malate concentrations, carbon dioxide evolution saturated.
- Taxon
- carrotDaucus carotat0
- Treatment
- higher external malate concentrationse0
- Outcome
- evolution of 14CO2e0
- Direction
- saturatese0
Not reportedOrgan / stage
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At higher external malate concentrations the evolution of 14CO2 saturates but accumulation in the tissue continues to rise”
t0“Carrot”
Claim · model-written summary
At higher external malate concentrations, tissue accumulation continued to rise.
- Taxon
- carrotDaucus carotat0
- Treatment
- higher external malate concentrationse0
- Outcome
- accumulation in the tissuee0
- Direction
- continues to risee0
Not reportedOrgan / stage
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“At higher external malate concentrations the evolution of 14CO2 saturates but accumulation in the tissue continues to rise”
t0“Carrot”
Claim · model-written summary
Tonoplast malate influx did not saturate at high external malate concentrations.
- Taxon
- carrotDaucus carotat0
- Treatment
- high external malate concentrationse0
- Outcome
- this influx does not saturatee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“this influx does not saturate at high external malate concentrations”
t0“Carrot”
Claim · model-written summary
Net malate efflux was very small but measurable.
- Taxon
- carrotDaucus carotat0
- Outcome
- net efflux of malate is very small but measurablee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The net efflux of malate is very small but measurable”
t0“Carrot”
Claim · model-written summary
External malate, chloride, nitrate, and sulfate did not stimulate efflux of radiolabeled malate.
- Taxon
- carrotDaucus carotat0
- Treatment
- external malate−, Cl−, NO3− or SO4−e0
- Outcome
- efflux of 14C-labelled malatee0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“The efflux of 14C-labelled malate is not stimulated by external malate−, Cl−, NO3− or SO4−”
t0“Carrot”
Claim · model-written summary
The authors infer an absence of plasmalemma systems exchanging internal malate for the tested anions.
- Taxon
- carrotDaucus carotat0
- Outcome
- no plasmalemma systems exchanging internal malate for these anionse0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
e0“There are therefore no plasmalemma systems exchanging internal malate for these anions”
t0“Carrot”