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At least 973 records · Page 54Linked to original sources
PubMed1975

Photo-inactivation of system II centers by carbonyl cyanide m-chlorophenylhydrazone in Chlorella pyrenoidosa.

In the presence of a high concentration of carbonyl cyanide m-chlorophenylhydrazone (CCCP) (4-10(-6) M), the S2 and S3 dark decays are accelerated and become biphasic with a first half-time of 0.6 s. The first fast phase of the decays does not correspond to a simple reduction of S2, S3 back to S0, S1 (i.e. to an acceleration of the deactivation reaction), but to a decrease in the number of oxygen-evolving System II centers. This photo-inactivation produced by CCCP is rapidly reversible in the dark.

Carbonyl Cyanide m-Chlorophenyl Hydrazone↗
PubMed1977

Effects of sodium azide on photosystem II of Chlorella pyrenoidosa.

The action of sodium azide on the electron transport chain was investigated by means of oxygen evolution, fluorescence and luminescence measurements. (1) The damping of the oxygen oscillations is progressively reduced with increasing azide concentration in the range of 10(-5) - 10(-1) M. (2) The rate of the dark decay of the S2 and S3 states is considerably slowed. The degree of slowing is dependent on concentration. (3) Luminescence is inhibited by azide both in the presence and absence of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU). (4) The fluorescence induction curve in strong light is modified in the presence of azide and its shape depends on azide concentration and on incubation time. (5) At a given time after a saturating flash, the fluorescence yield in the presence of azide is much higher than that of the control. It seems to be due to a general fluorescence increase rather than to a slower Q- reduction. (6) We tentatively propose an accelerated reduction of the primary donor P+ in state S2 and S3, by the intermediate donor Z in the presence of azide. Additionally, we have to assume that in the S2 and S3 states, some centers are blocked in an inactive low fluorescent form and that azide decreases their concentration.

Azides↗
PubMed1978

Turnover kinetics of photosystem I measured by the electrochromic effect in Chlorella.

The rise kinetics of the absorption changes induced at 515 nm and 480 nm by a flash were studied using two types of xenon flashes of different durations. The 'slow' rise of the absorption change (t 1/2 = 15--20 microseconds) observed by Cox and Delosme (1978 C.R. Acad. Sci. (Paris) Sér. D 282, 775--778) and Joliot was found to be due to double hits occurring in the reaction centers of System I during the flash. The turnover kinetics of the reaction centers of System I after a short flash were studied by a double flash method. They are in agreement with a second order reaction between P+-700 and its electron donor.

Chlorella↗
PubMed1985

Evidence that the variable fluorescence in Chlorella is recombination luminescence.

The fluorescence lifetime of oxygen-forming photosynthetic systems as a function of closed traps has been studied by several groups using light and poisons (usually 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)) to fix the closed trap state during the experiment. These measurements have now been carried out using light alone, by means of pump and probe laser pulses and a very efficient fast photomultiplier-digitizing system. It is found that the absolute amplitude of fast fluorescence (mean tau, approx. 0.3 ns) remains constant until over half the traps are filled. The amplitude of the slow fluorescence (tau approximately equal to 1.2 ns) increases with pump energy, and its response is best fit with a lag or finite rise-time of approx. 200 ps. This novel result is consistent with the hypothesis that the slow component of the fluorescence is actually recombination luminescence in the trap. Thus, the full trapping time, i.e., the time to form the P+I- state from an excitation in the O2 photosystem, is relatively slow.

Chlorella↗