OXYGEN QUENCHING OF CHLOROPHYLL FLUORESCENCE IN CHLOROPLASTS

Abstract— Three phases of chlorophyll a fluorescence quenching by O₂ are observed in green plants. The effects of various inhibitors on photosynthetic partial processes in chloroplasts were investigated in attempts to (1) localize the O₂-quenching sites and (2) assess possible physiological significance of O₂-quenching. Our results localize the most sensitive (and presumably functionally important) phase to a site between plastoquinone and the photosystem I acceptor, chlorophyll (P₇₀₀), possibly plastocyanin. It is suggested that PC may transfer electrons to oxygen in addition to P₇₀₀.     

KINETIC ANALYSIS OF THE INFLUENCE OF HYDROSTATIC PRESSURE ON BIOLUMINESCENCE OF GONYAULAX POLYEDRA

Abstract— Hydrostatic pressure was used as a probe to examine control mechanisms of bioluminescence in Gonyaulax polyedra. The initial effect of a pressure increase step is both to increase the intensity of the continuous light emission (glow) of the entire cell population and to increase the frequency of discrete flashes arising from single cells. Following the pressure application, however, the glow does not merely attain a new level but rather goes through various transient changes, whereby the kinetics of these changes are faster with a given higher pressure. A qualitative fit to several aspects of the pressure induced glow kinetics was generated by a simple reaction rate theory model. The effect of pressure upon the circadian rhythm control of bioluminescence was also investigated with the result being that no significant influence was observed under the experimental conditions.     

PHOTOSYNTHETIC ENERGY TRANSFER REVERSIBLY INHIBITED BY HYDROSTATIC PRESSURE*

Abstract— Hydrostatic pressure is found to affect reversibly the emission spectra of Porphyra perforata. At 1200atm phycoerythrin and phycocyanin fluorescence show a remarkable increase, whereas at the same time chlorophyll a (Chl a ) fluorescence decreases. Upon release of pressure the fluorescence intensities of the individual pigments return to their original levels. This effect indicates that hydrostatic pressure acts as a unique reversible inhibitor of energy transfer between phycobilins and Chi a in the chloroplast.
The effects of pressure and its release are relatively slow (minutes). It is suggested that pressure changes thylakoid membrane structure sufficiently to alter the critical distance between the phycobilisomes and Chl a , thus blocking the inductive resonance transfer of excitation energy.     

A STUDY OF THE FLASH INDUCED 518 NM ABSORBANCE CHANGE KINETICS UNDER ANAEROBIC CONDITIONS

The preillumination induced acceleration of the flash-induced 518 nm absorbance change (ΔA₅₁₈) decay was studied in lettuce leaves and chloroplasts. In leaves, the acceleration was inhibited by DCMU or reversibly by removal of oxygen. In chloroplasts with added ADP and phosphate and/or reconstructed electron transport, the acceleration was also inhibited by DCMU or the lack of O₂.
Anaerobic inhibition of ΔA₅₁₈ decay acceleration was no longer observed when hydroxylamine replaced water as electron donor to PSII. Anaerobiosis was also shown to reversibly inhibit the initial rate of FeCN reduction in chloroplasts. These results suggest the mechanism of anaerobic inhibition of ΔA₅₁₈ decay acceleration to be associated with the O₂ evolving system.