Abstract
Abstract The mechanisms of the coupling between ATP hydrolysis and proton transport catalyzed by the ATPases of the tonoplast and plasma membrane of maize (Lea mays L.) roots were investigated. Proton transport by the tonoplast ATPase was found to be much more sensitive to nitrate than ATP hydrolysis, being inhibited by 80% with almost no effect on hydrolysis at 5 mM NO3. Mercury was also found to be a potent inhibitor of this enzyme, inhibiting transport and hydrolysis by 50% at 60 and 100 μM, respectively. The same type of pattern was seen with other divalent cations. Millimolar concentrations of Cd2+, Co2+, Cu2+, and Zn2+ in the presence of Mg2+ inhibited proton transport significantly more than hydrolysis whereas Ba2+ and Ca2+ had little effect. Both free and ATP‐complexed species of these inhibitory cations appeared to be effective. When the influence of temperature was investigated, both the tonoplast and plasma membrane enzymes showed a similar pattern. ATP hydrolysis by both enzymes generally obeyed the Arrhenius model, increasing in rate between 10°C and 45°C. However, the rate of proton transport deviated from this pattern above 20°C, remaining constant up to approximately 30°C and decreasing to undetectable levels by 40°C. In the presence of 50 μM vanadate, ATP hydrolysis by the plasma membrane ATPase was reduced by approximately 60% versus 30% for proton transport. In addition, vanadate significantly decreased the first order rate constant, ki, indicating a lowering of proton efflux. The carboxyl‐modifying reagent N,N'‐dicyclohexylcarbodiimide nearly abolished transport with only a 50% reduction in ATP hydrolysis. These data arc interpreted in relation to whether the link between proton transport and ATP hydrolysis is direct or indirect for each enzyme.
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Claims 13
Claim · model-written summary
In maize roots, nitrate affected Proton transport as reported.
Zea maysOrganisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“Proton transport by the tonoplast ATPase was found to be much more sensitive to nitrate than ATP hydrolysis, being inhibited by 80% with almost no effect on hydrolysis at 5 mM NO3.”
Claim · model-written summary
In maize roots, Mercury affected transport as reported.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“Mercury was also found to be a potent inhibitor of this enzyme, inhibiting transport and hydrolysis by 50% at 60 and 100 μM, respectively.”
Claim · model-written summary
In maize roots, Mercury affected hydrolysis as reported.
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“Mercury was also found to be a potent inhibitor of this enzyme, inhibiting transport and hydrolysis by 50% at 60 and 100 μM, respectively.”
Claim · model-written summary
In maize roots, Cd2+, Co2+, Cu2+, and Zn2+ affected proton transport as reported.
- Treatment
- Cd2+, Co2+, Cu2+, and Zn2+e0
- Outcome
- proton transporte0
- Direction
- inhibitede0
- Comparator
- hydrolysise0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“Millimolar concentrations of Cd2+, Co2+, Cu2+, and Zn2+ in the presence of Mg2+ inhibited proton transport significantly more than hydrolysis whereas Ba2+ and Ca2+ had little effect.”
Claim · model-written summary
In maize roots, Ba2+ and Ca2+ affected proton transport as reported.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“Millimolar concentrations of Cd2+, Co2+, Cu2+, and Zn2+ in the presence of Mg2+ inhibited proton transport significantly more than hydrolysis whereas Ba2+ and Ca2+ had little effect.”
Claim · model-written summary
In maize roots, temperature affected ATP hydrolysis as reported.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“ATP hydrolysis by both enzymes generally obeyed the Arrhenius model, increasing in rate between 10°C and 45°C.”
e1“When the influence of temperature was investigated”
Claim · model-written summary
In maize roots, temperature affected rate of proton transport as reported.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“However, the rate of proton transport deviated from this pattern above 20°C, remaining constant up to approximately 30°C and decreasing to undetectable levels by 40°C.”
e1“When the influence of temperature was investigated”
Claim · model-written summary
In maize roots, temperature affected rate of proton transport as reported.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“However, the rate of proton transport deviated from this pattern above 20°C, remaining constant up to approximately 30°C and decreasing to undetectable levels by 40°C.”
e1“When the influence of temperature was investigated”
Claim · model-written summary
In maize roots, 50 μM vanadate affected ATP hydrolysis as reported.
- Treatment
- 50 μM vanadatee0
- Outcome
- ATP hydrolysise0
- Direction
- reducede0
- Value
- approximately 60%e0
- Comparator
- proton transporte0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“In the presence of 50 μM vanadate, ATP hydrolysis by the plasma membrane ATPase was reduced by approximately 60% versus 30% for proton transport.”
Claim · model-written summary
In maize roots, 50 μM vanadate affected proton transport as reported.
- Treatment
- 50 μM vanadatee0
- Outcome
- proton transporte0
- Direction
- reducede0
- Value
- 30%e0
- Comparator
- ATP hydrolysise0
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“In the presence of 50 μM vanadate, ATP hydrolysis by the plasma membrane ATPase was reduced by approximately 60% versus 30% for proton transport.”
Claim · model-written summary
In maize roots, vanadate affected first order rate constant, ki as reported.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“In addition, vanadate significantly decreased the first order rate constant, ki, indicating a lowering of proton efflux.”
Claim · model-written summary
In maize roots, N,N'‐dicyclohexylcarbodiimide affected transport as reported.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“The carboxyl‐modifying reagent N,N'‐dicyclohexylcarbodiimide nearly abolished transport with only a 50% reduction in ATP hydrolysis.”
Claim · model-written summary
In maize roots, N,N'‐dicyclohexylcarbodiimide affected ATP hydrolysis as reported.
Not reportedComparator
Organisms pictured · Representative pictures of the matched species, not figures from the paper.
Verbatim
t0“maize roots”
e0“The carboxyl‐modifying reagent N,N'‐dicyclohexylcarbodiimide nearly abolished transport with only a 50% reduction in ATP hydrolysis.”
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