Photosynthetic fractionation of the stable isotopes of oxygen and carbon

• Published in: Plant physiology (Bethesda) 1993-01, Vol.101 (1), p.37-47
• Main Authors: Guy, R.D. (University of British Columbia, Vancouver, BC, Canada), Fogel, M.L, Berry, J.A
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; ALGAE; ASPARAGUS; ATMOSPHERIC CHEMISTRY; BACILLARIOPHYCEAE; Biological and medical sciences; CARBON CYCLE; Carbon isotopes; CARBON-CARBON LYASES; CARBONE; CARBONO; CARBOXY-LYASES; CHEMICAL REACTIONS; CHEMISTRY; CYANOPHYTA; EARTH ATMOSPHERE; ECHANGE GAZEUX; ELEMENTS; ENVIRONMENTAL SCIENCES; ENZYMES; FERREDOXIN; FLUIDS; FOOD; FOTOSINTESIS; FRACCIONAMIENTO; Fractionation; FRACTIONNEMENT; Fundamental and applied biological sciences. Psychology; GASES; GLOBAL ASPECTS; HELIUM; INTERCAMBIO DE GASES; ISOTOPE; Isotope effects; ISOTOPES; ISOTOPOS; LYASES; MAGNOLIOPHYTA; MAGNOLIOPSIDA; MATEMATICAS; MATHEMATICAL MODELS; MATHEMATIQUE; Mesophyll cells; Metabolism; Metabolism and Enzymology; METALLOPROTEINS; MINERAL CYCLING; MODELE MATHEMATIQUE; MODELOS MATEMATICOS; NONMETALS; ORGANIC COMPOUNDS; OXIGENO; OXYGEN; Oxygen isotopes; OXYGENE; PHOTOCHEMICAL REACTIONS; Photorespiration; PHOTOSYNTHESE; PHOTOSYNTHESIS; Photosynthesis, respiration. Anabolism, catabolism; Plant physiology and development; PLANTS; PROTEINS; RARE GASES; Respiration; RIBULOSE DIPHOSPHATE CARBOXYLASE; SPINACH; SPINACIA OLERACEA; STABLE ISOTOPES; SYNTHESIS; VEGETABLES 540120 > Environment, Atmospheric-- Chemicals Monitoring & Transport-- (1990-)
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.101.1.37

Isotope discrimination during photosynthetic exchange of and CO2 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 (delta, where 1 + delta/1OOO equals the isotope effect, k16/k18 or k12/k13) was determined by analysis of residual substrate (O2 or CO2). The delta for the Mehler reaction, mediated by ferredoxin or methylviologen, was 15.3%. 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 discrimination: 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 delta for O2 consumption catalyzed by glycolate oxidase was 22.7 per thousand. The expected overall delta, for photorespiration is about 21.7 per thousand. Consistent with this, when Asparagus sprengeri Regel mesophyll cells approached the compensation point within a sealed vessel, the delta 18O of dissolved O2 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 O cycle and indicate that photorespiration plays a significant part in determining the isotopic composition of atmospheric oxygen