Changes in photosynthetic activity of the diatom Phaeodactylum tricornutum in a culture of limited volume

Changes in photosynthetic activity of a marine diatom duringalgal growth were studied with a typical culture medium formarine algae, ASP-2 (l). As the algal specimen, Phaeodactylumtricornutum was used for the experiments. Nitzschia closteriumand Chaetoceros sp. were also supplementarily used. Photosynthetic and p-benzoquinone Hill activities remarkablychanged with time during algalgrowth; with maximum activityfound in cells at log phase. A rapid decrease occurred in theinterphase from the log to stationary phase. The activity changewas not accompanied by variation in photosynthetic pigment content. The low concentration of phosphorus source was suggested asthe main cause for the change. On supply of extra inorganicphosphate, the time length for holding high photosynthetic activitybecame longer; or, the activity of the cells at stationary phaserecovered at least partly even in the dark. Dark recovery wasnot accompanied by either algal growth or an increase in thecontent of photosynthetic pigments. Inactivation of photosynthesis in the stationary growth phaseand activation by added phosphate in the dark were inferredto be due to changes in activities of both the CO₂-fixing andelectron transfer systems. The observed activity change maynot be attributable to a deficiency in inorganic phosphate asthe substrate for photophosphorylation. Similar changes in photosynthetic activity were also observedwith Nitzschia closterium and Chaetoceros sp. (Received January 30, 1971; )