Chlorophyll fluorescence transients of Photosystem II membrane particles as a tool for studying photosynthetic oxygen evolution

The rise of the chlorophyll fluorescence yield of Photosystem II (PS II) me mbranes as induced by high-intensity actinic light comprises only two disti nct phases: (1) the initial O-J increase and (2) the subsequent J-P increas e. Partial inhibition of the PS II donor side by heating or washing procedu res which remove peripheral PS II proteins or cofactors of the oxygen-evolv ing complex results in decrease of magnitude and rate of the J-P phase. The rate constant of the J-P increase is directly proportional to the steady-s tate rate of oxygen evolution; complete suppression of the J-P phase corres ponds to full inhibition. A characteristic dip after J-level is observed on ly in Tris-washed or severely heated PS II membranes; manganese release cor relates with appearance of the dip after J-level as verified by EPR spectro scopy. Presence of stabilizing cosolutes (glycine betaine, sucrose) or addi tion of donor-side cofactors (bicarbonate, chloride, calcium) to PS II memb ranes before heating (47 degreesC, 5 min) diminishes J-P phase suppression and prevents dip appearance, whereas the addition after heating is without effect. In conclusion, analysis of chlorophyll fluorescence transients of P S II membranes is a potentially useful tool for investigations on photosynt hetic oxygen evolution. A decreased rate of the J-P phase can be employed a s a convenient indicator for partial inhibition of oxygen-evolution activit y; the appearance of a dip after J-level is suggestive of manganese release .