C. Maurindefossez et Y. Legal, DIEL PERIODICITY OF GLUTAMINE-SYNTHETASE ACTIVITY DURING THE CELL-CYCLE OF EMILIANIA-HUXLEYI, Plant physiology and biochemistry, 36(3), 1998, pp. 233-236
Light-dark regulation of glutamine synthetase (GS; EC 6.3.1.2) was inv
estigated by following the development of activity and the time-course
of the cell-cycle of the marine coccolithophorid, Emiliania huxleyi,
under a 16-h photoperiod in synchronous cultures. GS activity showed m
arked diel periodicity by exhibiting a maximum value during the dark p
eriod and a minimum during the light. Our results suggest that regulat
ion of GS activity during the light-dark cycle probably does not opera
te only through activation/deactivation mechanisms. Cell division took
place from the end of the dark to the first hours of the light period
. The succession of the cell-cycle events was analysed by flow cytomet
ry. Variations in GS activity appeared to match the demands of the cel
l for glutamine, increasing during the G(1) phase in the light, and re
maining at a high level during DNA synthesis in the dark. (C) Elsevier
, Paris.