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Related Experiment Videos

CO2 reduction by intact chloroplasts under a diminished proton gradient.

J E Tillberg, C Giersch, U Heber

    Biochimica Et Biophysica Acta
    |July 7, 1977
    PubMed
    Summary
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    Intrathyroidal pH in chloroplasts was measured using 9-aminoacridine. Uncoupling amines altered pH and oxygen evolution, challenging current chemiosmotic models.

    Area of Science:

    • Plant Physiology
    • Photosynthesis Research
    • Biochemistry

    Background:

    • 9-Aminoacridine is a fluorescent probe used to measure intrathylakoid pH in chloroplasts.
    • Accurate pH measurements require correction for light-dependent binding of the probe to thylakoid membranes.

    Purpose of the Study:

    • To investigate the relationship between intrathylakoid pH, proton transport, and photosynthetic activity in intact chloroplasts.
    • To evaluate the effects of uncoupling agents on proton gradients and ATP synthesis.

    Main Methods:

    • Utilized 9-aminoacridine fluorescence to monitor intrathylakoid pH changes during nitrite and CO2 reduction.
    • Measured rates of CO2-dependent oxygen evolution.
    • Assessed light-induced membrane potential using the 515 nm signal.

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  • Determined ATP/ADP ratios under various conditions.

    • Main Results:

    • Intrathylakoid proton concentration increased during nitrite reduction and decreased during CO2 reduction.
    • Uncoupling amines (NH3, cyclohexylamine) decreased intrathylakoid pH but stimulated CO2-dependent oxygen evolution.
    • Inhibitors like FCCP and nigericin affected CO2 reduction and intrathylakoid pH.
    • Light-induced membrane potential was largely unaffected by low concentrations of uncoupling amines but reduced by FCCP.
    • ATP/ADP ratios remained high with NH4Cl but were reduced to dark levels by FCCP.

    Conclusions:

    • The observed effects of uncoupling amines on photosynthesis and proton gradients are difficult to reconcile with the standard chemiosmotic hypothesis.
    • Further refinement of models describing proton transport and energy transduction in chloroplasts is needed.