Hydrostatic pressure: a reversible inhibitor of primary photosynthetic processes.

Primary photosynthetic processes under pressures of up to 1300 atm were studied by means of chlorophyll fluorescence induction (Kautsky-effect) and compared to simultaneous oxygen exchange transients determined polarographically. Chlorophyll fluorescence induction was affected by increased hydrostatic pressure in three distinct ways: 1. At 400 atm loss of the first fluorescence drop (I—D transient), reflecting inhibition of PSI activity; 2. at 400 —1200 atm suppression of the fluores­ cence peak (D —P —S transient), indicating a block at the electron donor site of PS II; 3. at 800 —1200 atm flattening of the first fluorescence rise (O —I transient), suggesting a loss of ex­ citation energy within the pigment system. Pressure effects on oxygen exchange include inhibition of transient oxygen uptake and stimulation of the initial oxygen burst, which is paralleled by loss of the first transient fluorescence drop. Inhibition of the second oxygen burst is accompanied by the elimination of the transient fluorescence peak. The first burst only decreases with pressures exceeding 800 atm, as does the initial fluorescence rise. All pressure effects on fluorescence and oxygen exchange were reversible. Hydrostatic pressure appears to be a useful multilateral inhibitor in the study of primary photosynthetic reactions.