Photosynthetic fractionation of the stable isotopes of oxygen and carbon

Journal Article · Fri Jan 01 00:00:00 EST 1993 · Plant Physiology; (United States)

OSTI ID:6778266

Guy, R D ^[1]; Fogel, M L; Berry, J A ^[2]

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1. Carnegie Institution of Washington, Stanford, CA (United States)
2. Carnegie Inst. of Washington, Washington, DC (United States)

Isotope discrimination during photosynthetic exchange of O[sub 2] and CO[sub 2] was measured using enzyme, thylakoid, and whole cell preparations. Evolved oxygen from isolated spinach thylakoids was isotopically identical (within analytical error) to its source water. Similar results were obtained with Anacystis nidulans Richter and Phaeodactylum tricornutum Bohlin cultures purged with helium. For consumptive reactions, discrimination ([triangle], where 1 + [triangle]/1000 equals the isotope effect, k[sup 16]/k[sup 18] or k[sup 12]/k[sup 13]) was determined by analysis of residual substrate (O[sub 2] or CO[sub 2]). The [triangle] for the Mehler reaction, mediated by ferredoxin or methylviologen, was 15.3[per thousand]. Oxygen isotope discrimination during oxygenation of ribulose-1,5-bisphosphate (RuBP) catalyzed by RuBP carboxylase/oxygenase (Rubisco) was 21.3[per thousand] and independent of enzyme source, unlike carbon isotope dicrimination: 30.3[per thousand] for spinach enzyme and 19.6 to 23[per thousand] for Rhodospirillum rubrum and A. nidulans enzymes, depending on reaction conditions. The [triangle] for O[sub 2] consumption catalyzed by glycolate oxidase was 22.7[per thousand]. Consistent with this, when Asparagus sprengeri Regel mesopyll cells approached the compensation point within a sealed vessel, the [delta][sup 18]O of dissolved O[sub 2] came to a steady-state value of about 21.5[per thousand] relative to the source water. The results provide improved estimates of discrimination factors in several reactions prominent in the global oxygen cycle and indicate that photorespiration plays a significant part in determining the isotopic composition of atmospheric oxygen. 47 refs., 8 figs., 2 tabs.

• OSTI ID: 6778266
• Journal Information: Plant Physiology; (United States), Vol. 101:1; ISSN 0032-0889
• Country of Publication: United States
• Language: English

Related Subjects

54 ENVIRONMENTAL SCIENCES
OXYGEN
MINERAL CYCLING
PHOTOSYNTHESIS
GLOBAL ASPECTS
ATMOSPHERIC CHEMISTRY
CARBON CYCLE
EARTH ATMOSPHERE
FERREDOXIN
HELIUM
MATHEMATICAL MODELS
PLANTS
RIBULOSE DIPHOSPHATE CARBOXYLASE
SPINACH
STABLE ISOTOPES
CARBON-CARBON LYASES
CARBOXY-LYASES
CHEMICAL REACTIONS
CHEMISTRY
ELEMENTS
ENZYMES
FLUIDS
FOOD
GASES
ISOTOPES
LYASES
MAGNOLIOPHYTA
MAGNOLIOPSIDA
METALLOPROTEINS
NONMETALS
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
PROTEINS
RARE GASES
SYNTHESIS
VEGETABLES
540120* - Environment
Atmospheric- Chemicals Monitoring & Transport- (1990-)