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BIOENERGETICS AND PHOTOSYNTHESIS

Photosynthetic Utilization of Bicarbonate in Zostera marina Is Reduced by Inhibitors of Mitochondrial ATPase and Electron Transport¹

Department of Botany, Stockholm University, SE–106 91 Stockholm, Sweden (H.C.); and Kristineberg Marine Research Station, SE–450 34 Fiskebaeckskil, Sweden (L.A.)

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 µM 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.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Herman Carr (carr{at}botan.su.se).

www.plantphysiol.org/cgi/doi/10.1104/pp.107.115584

^* Corresponding author; e-mail carr{at}botan.su.se.

Received January 10, 2008; accepted April 15, 2008; published April 23, 2008.