THE POSITION OF C14 IN SUNFLOWER LEAF METABOLITES AFTER EXPOSURE OF LEAVES TO SHORT PERIOD PHOTOSYNTHESIS AND DARKNESS IN AN ATMOSPHERE OF C14O2

Abstract

Detached sunflower leaves were allowed to photosynthesize in strong light for a short period in an atmosphere of C14O2, after which the carbohydrates (sucrose, glucose, fructose, dextrin, and starch), alanine, and malic acid were isolated and the location of the C14 detd. The same compounds were isolated and degraded from leaves which had been exposed to C14O2 in darkness. In the photosynthesis expts.: (a) The monosaccharides contained no label. (b) Dextrin approached uniform distribution of carbon more rapidly than the other substances. (c) The labelling of alanine was similar to that of sucrose. (d) Malic acid remained predominantly carboxyl labeled during all exposures. In the dark expts.: (a) Of the carbohydrates, glucose, fructose, and sucrose, only the sucrose contained label. When the sucrose was inverted and degraded, the invert sugar was labeled only in carbon atoms 3 and 4. (b) The alanine and malic acid were labeled only in the carboxyl carbon. The data indicate that before label can occur in positions other than carbon atoms 3 and 4 of sugar and the carboxyl carbon of amino acids and organic acids, light is necessary to initiate the cycle which synthesizes the C2 acceptor.