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PubMed1977

[Ultrastructural localization of photosystem I and II active sites in chloroplasts in situ].

Activities related to photosystem I and photosystem II are cytochemically localized at the electron microscope level by using suitable artificial electron donors and acceptors with, or without, factors uncoupling the light-induced electron flow between the two systems. Photo-oxidation of DAB, insensitive to DCMU, is linked to photosystem I activity. It occurs within the grana and stroma membranes of the chloroplasts. Photo-reduction of TC-NBT sensitive to DCMU, is a photosystem II mediated reaction. It is trapped within the grana membranes.

Chloroplasts↗
PubMedDate not supplied

[Relation of the growth of Anabaena variabilis cyanophages to photosynthesis and respiration].

Cyanophages A-1 (L) and A-4C (L) grow within the cells of Anabaena variabilis under aerobic conditions in the dark in the presence of endogenous or exogenous (surcose) sources of energy. DNP inhibits the growth of cyanophages in the light and almost completely supresses it in the dark, o-phenanthroline entirely supresses the growth in both cases. DCMU has almost no effect on the yield of the virus in the light. Virus particles can apparently be synthesized at the account of the energy of both oxidative and cyclic photophosphorylation.

Cyanobacteria↗
PubMed1979

[Effect of cations on the quantum yield and the lifetime of the chloroplast fluorescence].

The interrelationship between the cation-induced fluorescence changes and the state of the photosystem 2 (PS-2) reaction centers for pea chloroplasts and their osmotic fragments was studied. The effects of K+ and Mg2+ on the fluorescence quantum yield (phi f1) under varying light intensities as well as on the fluorescence lifetime (tau f1) in the saturating light were demonstrated. K+ induces the decrease in tau f1; Mg2+ exerts an opposite effect. The effects were more pronounced when the reaction centers of PS-2 were converted into an inactive state by illuminating the sample with a saturating light or by adding DCMU. Under these conditions the cations' effect on tau f1 was accompanied by proportional changes in tau f1. It was concluded that in Mg-deficient chloroplasts an efficient channel of the excitation quenching appears in antenna chlorophyll of PS-2 with the rate constant of 7 . 10(8) s-1. The simultaneous measurements of tau f1 by phase and modulation type techniques allowed to reveal the emission heterogeneity within the nanosecond time interval and the DCMU-sensitive delayed fluorescence with the lifetime exceeding 10(-7) s and the overall quantum yield approximately equal to 2 . 10(-3).

Chloroplasts↗
PubMed1973

Lipid biosynthesis by isolated plastids from greening pea, Pisum sativum.

Isolated etioplasts from 8-day-old dark-grown pea seedlings incorporated [1-(14)C]acetate into lipid at a relatively low rate. Plastids from seedlings that had been illuminated for at least 2 hr showed an enhanced incorporation provided the plastids were illuminated during incubation with the labeled acetate. Dark incubation or the addition of 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) decreased the acetate-incorporating activity of the developing chloroplasts to the level observed with etioplasts. Light had a marked effect on the type of fatty acid into which acetate was incorporated by the developing chloroplasts. Unsaturated fatty acids (mostly oleic acid) accounted for 60-80% of the incorporated label if the plastids were illuminated, but in the dark or in the presence of DCMU the unsaturated acids accounted for only 0-15% of the label incorporated into lipid. The effect of ATP on incorporation was dependent on the maturity of the chloroplasts; mature pea chloroplasts were inhibited by ATP, whereas in developing plastids there was a slight stimulation by ATP. Inhibition of acetate incorporation into lipid by DCMU appears to be due to inhibition of noncyclic phosphorylation. Incorporation was restored by reduced 2,3,5,6-tetramethylphenylenediamine, which restored phosphorylation, but not by reduced N,N,N',N'-tetramethylphenylenediamine.

Acetates↗