Radioactive contamination of the marine environment: Uptake and distribution of³H in Dunaliella bioculata

The marine flagellate Dunaliella bioculata, which is easily cultivated under laboratory conditions, is a suitable organism for assessing the importance of the radioactive contamination by³H bound to organic molecules. We have studied the uptake of the following tritiated precursors: thymidine-methyl-³H, adenine-2-³H, uridine-5-³H, l-leucine-4-³H, glycine-2-³H, l-arginine-3.4-³H, 1-aspartic acid-2. 3-³H, 1-phenylalanine-2.3-³H, D-glucose-2-³H and D-glucose-6-³H. Under the experimental conditions (2000 lux; incubation time 30 min), all tritiated molecules are taken up by D. bioculata. Their intracellular concentration may reach that of the external medium. However, leucine and adenine accumulate in the algae: their respective concentrations are 10 and 100 times higher than in the culture medium. The molecular distribution of³H has been studied by various biochemical techniques and by sieve chromatography on sepharose 4B. It has been found that more l-leucine-4-³H is incorporated into acid and acetone soluble substances than into proteins. Adenine-2-³H is mainly incorporated into macromolecules of biological significance (RNA, DNA). CsCl gradient centrifugation has shown that the total DNA of Dunaliella is constituted by a major (π{variant}=1.707 g/cm³) and by a minor (π{variant}=1.693 g/cm³) component.