Energetic factors affecting carbon dioxide fixation in isolated chloroplasts
Light- and HCO/sub 3/-saturated (10 millimolar) rates of O/sub 2/ evolution (120 to 220 micromoles O/sub 2/ per milligram chlorophyll per hour), obtained with intact spinach chloroplasts, are decreased up to 3-fold by changes in assay conditions such as omission of catalase from the medium, the use of high (greater than or equal to 1 millimolar) inorganic phosphate, inclusion of NO/sub 2/- as an electron acceptor, or bright illumination at low partial pressures of O/sub 2/. These inhibitions may be reversed by addition of uncoupling levels of NH/sub 4/Cl or of antimycin concentrations that partially block cyclic electron transfer between cytochrome b/sub 6/ and cytochrome f. Measurements of the pH gradient across the thylakoid membrane with the fluorescent probe, 9-aminoacridine, indicate that changes in ..delta..pH are sufficient to account for both the inhibited and restored rates of electron transport. It follows that the rate of HCO/sub 3/-saturated photosynthesis may be restricted by a proton gradient back pressure under these conditions. The rate of O/sub 2/ evolution is also decreased 3-fold when ambient CO/sub 2/ (0.63 millimolar HCO/sub 3/- at pH 8.1) is used in place of saturating HCO/sub 3/- and chloroplasts are illuminated aerobically with catalase and a low level (0.25 millimolar) of K/sub 2/HPO/sub 4/. Only inhibitory effects are observed with additions of antimycin or NH/sub 4/Cl. Under these conditions, excessive photophosphorylation or a large pH gradient does not limit the rate of photosynthesis.
- Research Organization:
- Brookhaven National Lab. (BNL), Upton, NY (United States)
- OSTI ID:
- 6786682
- Journal Information:
- Plant Physiol.; (United States), Vol. 65:3
- Country of Publication:
- United States
- Language:
- English
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63 RADIATION, THERMAL, AND OTHER ENVIRON. POLLUTANT EFFECTS ON LIVING ORGS. AND BIOL. MAT.
AMMONIUM CHLORIDES
BIOLOGICAL EFFECTS
ANTIBIOTICS
CHLOROPLASTS
SENSITIVITY
PH VALUE
PHOTOSYNTHESIS
ELECTRON TRANSFER
BIOCHEMICAL REACTION KINETICS
CARBON DIOXIDE
CHLOROPHYLL
ENERGY TRANSFER
INHIBITION
METABOLISM
PHOSPHORYLATION
SPINACH
VISIBLE RADIATION
AMMONIUM COMPOUNDS
AMMONIUM HALIDES
CARBON COMPOUNDS
CARBON OXIDES
CARBOXYLIC ACIDS
CELL CONSTITUENTS
CHALCOGENIDES
CHEMICAL REACTIONS
CHLORIDES
CHLORINE COMPOUNDS
DRUGS
ELECTROMAGNETIC RADIATION
FOOD
HALIDES
HALOGEN COMPOUNDS
HETEROCYCLIC ACIDS
HETEROCYCLIC COMPOUNDS
KINETICS
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
OXIDES
OXYGEN COMPOUNDS
PHOTOCHEMICAL REACTIONS
PHYTOCHROMES
PIGMENTS
PORPHYRINS
RADIATIONS
REACTION KINETICS
SYNTHESIS
VEGETABLES
550200* - Biochemistry
550300 - Cytology
551000 - Physiological Systems
560303 - Chemicals Metabolism & Toxicology- Plants- (-1987)