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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‐replete cells of the marine diatom Phaeodactylum tricornutum Bohlin, the rate of dark respiration was high and markedly inhibited (62%–74%) in the presence of oligomycin. In contrast, the rate of dark respiration in nitrogen‐deprived cells was about half that in nitrogen‐replete cells but was only slightly inhibited (16%–30%) by oligomycin. Consistent with these effects on rates of dark respiration, oligomycin decreased the ATP level and the ATP:ADP ratio by about 40% in nitrogen‐replete cells incubated in darkness but had a negligible effect on the ATP level and ATP:ADP ratio in nitrogen‐deprived cells. In sodium and nitrogen‐deprived cells, the rate of dark respiration was greater than that in nitrogen‐replete cells, but there was little effect of oligomycin on the rate of dark respiration. In light‐limited cells, the rate of dark respiration was similar to that in nitrogen‐deprived cells, but the inhibition (57%) in the presence of oligomycin was greater. These results suggest that most of the O2 consumption by nitrogen‐replete cells was linked to mitochondrial ATP synthesis and that the rate of mitochondrial ATP synthesis in nitrogen‐deprived and sodium and nitrogen‐deprived cells was low. The potential implications of these results for our understanding of maintenance respiration are discussed.