Studies on the fractionation of oxygen isotopes at the natural abundance level during photosynthesis



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Even though many experiments have been performed to determine the precursor of photosynthetic oxygen, few have given very conclusive results. The measurements are difficult for a number of reasons, both chemical and biological; and experimental compromises may largely negate the results. Because of the CO₂-water isotopic exchange and the probability that in cells this exchange reaches equilibrium very quickly (17, 24), no attempt was made here to use O¹⁸ enriched water or CO₂. Rather O¹⁸ at the natural abundance level was used to look at the isotopic composition of water and the photosynthetic oxygen evolved from it. This thesis is concerned with the O¹⁸ enrichment anomalies found by Schultz (37), and with the enrichment anomalies extant in the literature, observed while studying the origin of photosynthetic oxygen