Effect of oligomycin on dark respiration in the marine diatom Phaeodactylum tricornutum (Bacillariophyceae): Implications for determination of maintenance respiration

Oligomycin is an inhibitor of the mitochondrial ATP synthase, In nitrogen-r eplete cells of the marine diatom Phaeodactylum tricornutum Bohlin, the rat e of dark respiration was high and markedly inhibited (62%-74%) in the pres ence of oligomycin, In contrast, the rate of dark respiration in nitrogen-d eprived cells was about half that in nitrogen-replete cells but was only sl ightly inhibited (16%-30%) by oligomycin. Consistent with these effects on rates of dark respiration, oligomycin decreased the ATP level and the ATP:A DP ratio by about 40% in nitrogen-replete cells incubated in darkness but h ad a negligible effect on the ATP level and ATP:ADP ratio in nitrogen-depri ved cells. In sodium and nitrogen-deprived cells, the rate of dark respirat ion was greater than that in nitrogen-replete cells, but there was little e ffect of oligomycin on the rate of dark respiration. In light-limited cells , the rate of dark respiration was similar to that in nitrogen-deprived cel ls, but the inhibition (57%) in the presence of oligomycin was greater, The se results suggest that most of the O-2 consumption by nitrogen-replete cel ls was linked to mitochondrial ATP synthesis and that the rate of mitochond rial ATP synthesis in nitrogen-deprived and sodium and nitrogen-deprived ce lls was low. The potential implications of these results for our understand ing of maintenance respiration are discussed.