Photosynthetic utilization of bicarbonate in Zostera marina is reduced by inhibitors of mitochondrial ATPase and electron transport.
When Zostera marina was irradiated after a period of darkness, initiation of photosynthetic O2 evolution occurred in two phases. During a lag phase, lasting 4 to 5 min, photosynthesis was supported by a diffusive entry of CO2. Photosynthesis then rapidly increased to its full rate. Tris buffer, at a concentration of 50 mm, completely inhibited this increase without affecting CO2-supported photosynthesis during the lag phase. These results verify that the increase in photosynthesis after the lag phase depended on an activation of bicarbonate (HCO3-) utilization through acid zones generated by proton pumps located to the outer cell membrane. In similar experiments, 6.25 microm of the mitochondrial ATPase blocker oligomycin inhibited photosynthetic HCO3(-) utilization by more than 60%. Antimycin A, a selective blocker of mitochondrial electron transport, caused a similar inhibition of HCO3(-) utilization. Measurements at elevated CO2 concentrations verified that neither oligomycin nor antimycin interfered with linear photosynthetic electron transport or with CO2 fixation. Thus, a major part of the ATP used for the generation of acid zones involved in HCO3(-) utilization in Z. marina was derived from mitochondrial respiration.
Carr
Herman
H
Department of Botany, Stockholm University, SE-106 91 Stockholm, Sweden. carr@botan.su.se
Axelsson
Lennart
L
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors* / Q000378:metabolism; D001639:Bicarbonates / Q000378:metabolism*; D004579:Electron Transport; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D008928:Mitochondria / Q000187:drug effects* / Q000201:enzymology; D010788:Photosynthesis; D035962:Zosteraceae / Q000201:enzymology / Q000378:metabolism*
D001639:Bicarbonates; D004791:Enzyme Inhibitors; D000251:Adenosine Triphosphatases