Abstract
Abstract Chloroplasts suspended in the presence of NH4Cl have been shown to take up ammonium ion from the medium on illumination. NH4+ uptake approached a maximum with increasing NH4Cl concentration, and was associated with a parallel inhibition of the light-induced pH change. Maximal values for rate and extent of NH4+ uptake did not vary greatly with pH. However, below pH 7 the apparent Km for NH4Cl rose markedly with decreasing pH, and this reflected a calculated Km for NH3 which did not change greatly. Above pH 7, the Km for NH3 increased with increasing pH, and this was associated with a loss of coupling between electron flow and energy conservation. It has been concluded that NH3 is the active species in NH4+ uptake. NH4+ and H+ uptake accompanying ferricyanide reduction in the Hill reaction have been compared with uptake linked to N-methylphenazonium methosulfate-catalyzed electron flow. It was found that between 2 and 3 H+ or NH4+ ions were taken up into the chloroplast per electron transported to ferricyanide. Competitive inhibition of NH4+ uptake under conditions of photophosphorylation has been found. Phlorizin at a concentration which completely inhibited photophosphorylation had little effect on the rate of H+ or NH4+ uptake, but partially reduced the extent of NH4+ uptake. A mechanism for NH4+ uptake has been proposed. It has been suggested that, on acidification of the chloroplast interior following H+ uptake, the equilibration of NH3 across the chloroplast membrane is displaced, and that more NH3 enters to replace that lost by association with H+. The net accumulation of NH4+ leads to an uptake of Cl- by diffusion, and the increased osmolarity within the chloroplasts leads to water movement and swelling. The mechanism proposed also provides a general mechanism for uncoupling by amines.
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Claims 16
Claim · model-written summary
Illuminated chloroplasts took up ammonium ion in NH4Cl.
Not reportedTaxon
Verbatim
e0“Chloroplasts suspended in the presence of NH4Cl have been shown to take up ammonium ion from the medium on illumination”
Claim · model-written summary
NH4+ uptake approached a maximum as NH4Cl concentration increased.
Not reportedTaxon
Verbatim
e0“NH4+ uptake approached a maximum with increasing NH4Cl concentration”
Claim · model-written summary
NH4+ uptake was associated with inhibition of the light-induced pH change.
Not reportedTaxon
Verbatim
e0“NH4+ uptake approached a maximum with increasing NH4Cl concentration, and was associated with a parallel inhibition of the light-induced pH change”
Claim · model-written summary
Maximal NH4+ uptake rate and extent varied little with pH.
Not reportedTaxon
Verbatim
e0“Maximal values for rate and extent of NH4+ uptake did not vary greatly with pH”
Claim · model-written summary
Below pH 7, apparent Km for NH4Cl rose as pH decreased.
Not reportedTaxon
Verbatim
e0“below pH 7 the apparent Km for NH4Cl rose markedly with decreasing pH”
Claim · model-written summary
Below pH 7, calculated Km for NH3 changed little.
Not reportedTaxonTreatment
Verbatim
e0“this reflected a calculated Km for NH3 which did not change greatly”
Claim · model-written summary
Above pH 7, Km for NH3 increased with pH.
Not reportedTaxon
Verbatim
e0“Above pH 7, the Km for NH3 increased with increasing pH”
Claim · model-written summary
Above pH 7, coupling between electron flow and energy conservation was lost.
- Outcome
- loss of coupling between electron flow and energy conservatione0
Not reportedTaxon
Verbatim
e0“this was associated with a loss of coupling between electron flow and energy conservation”
Claim · model-written summary
The authors concluded that NH3 is the active species in NH4+ uptake.
Not reportedTaxon
Verbatim
e0“NH3 is the active species in NH4+ uptake”
Claim · model-written summary
Between 2 and 3 H+ or NH4+ ions entered chloroplasts per electron transported to ferricyanide.
Not reportedTaxon
Verbatim
e0“between 2 and 3 H+ or NH4+ ions were taken up into the chloroplast per electron transported to ferricyanide”
Claim · model-written summary
Photophosphorylation conditions competitively inhibited NH4+ uptake.
Not reportedTaxonComparator
Verbatim
e0“Competitive inhibition of NH4+ uptake under conditions of photophosphorylation has been found”
Claim · model-written summary
Phlorizin at a concentration completely inhibited photophosphorylation.
Not reportedTaxonComparator
Verbatim
e0“Phlorizin at a concentration which completely inhibited photophosphorylation”
Claim · model-written summary
Phlorizin had little effect on H+ or NH4+ uptake rate.
Not reportedTaxonComparator
Verbatim
e0“Phlorizin at a concentration which completely inhibited photophosphorylation had little effect on the rate of H+ or NH4+ uptake”
Claim · model-written summary
Phlorizin partly reduced NH4+ uptake extent.
Not reportedTaxonComparator
Verbatim
e0“Phlorizin at a concentration which completely inhibited photophosphorylation had little effect on the rate of H+ or NH4+ uptake, but partially reduced the extent of NH4+ uptake”
Claim · model-written summary
The proposed mechanism links chloroplast interior acidification to NH3 entry and NH4+ accumulation.
Not reportedTaxon
Verbatim
e0“on acidification of the chloroplast interior following H+ uptake, the equilibration of NH3 across the chloroplast membrane is displaced, and that more NH3 enters to replace that lost by association with H+”
Claim · model-written summary
The proposed mechanism links NH4+ accumulation to chloride uptake by diffusion and chloroplast swelling.
Not reportedTaxon
Verbatim
e0“The net accumulation of NH4+ leads to an uptake of Cl- by diffusion, and the increased osmolarity within the chloroplasts leads to water movement and swelling”