Springer Online Journal Archives 1860-2000
Summary When discs punched out of the median part of the phylloid of Laminaria saccharina Lamour. were exposed to H14CO3 - in the light for periods of 10 sec to 10 min, 14C was rapidly incorporated into various photosynthetic products. As compared with dark fixation, 14C-photosynthesis increased exponentially during the first 60 sec of incubation in H14CO3 -. Fixation rates were found to be 76 μmol CO2·dm-2·h-1 or 100 μmol CO2·mg-1 chlorophyll a·h-1. Eighty-five per cent of the total 14C assimilated after 10 sec was fixed in phosphoglycerate and in the sugar monophosphates, 2% in the sugar diphosphates, and only 3.5% in malate and aspartate. While the radioactivity of malate and aspartate only rose to a constant level, the percentage of the total 14C in phosphoglycerate and-to a lower extent-that in the sugar monophosphates rapidly decreased with the duration of light exposure. Simultaneously, mannitol and glycine+serine became labelled with 43% and 32% respectively of the total 14C after 10 min light fixation. In the dark, the percentage of the total 14C in malate decreased with the time of H14CO2--incubation, while there was a remarkable increase in radioactivity of aspartate and glutamate. Within 60 min darkness no labelling of mannitol was found. From the present results it is concluded that the photosynthetic carbon cycle first described by Bassham and Calvin operates in Laminaria saccharina.
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