R. subcapitata was grown continuously in MBL medium (Nichols,
1973) with additional vitamin B1, at a temperature of 19 C under a
16:8 h light: dark cycle with a light intensity (photon flux density)
of approximately 90 mmol m2 sec1
. The cells were 14C-labeled, in
order to trace subsequent carbon incorporation by D. magna, by
adding 1.22 GBq of NaH14CO3 (Amersham; specific activity
1.998 GBq mmol1
) to 3L of R. subcapitata in MBL medium and
incubating for one week before exposure to gamma-radiation.
2