Coupling of replication, transcription and translation under two different steady state conditions in Allium cepa meristems.

Replication, transcription and translation rates have been analysed in root meristems of Allium cepa L. growing under two different steady conditions (10 and 25 degrees C). Cell size and the relative duration of cycle compartments are similar for both steady states, while cycle time is four times longer at the lower temperature. Though replication and translation rates per cycle are similar, at the lower temperature there is a doubling in the production of rRNA which coincides with the presence of enlarged nucleoli. There is some reduction in the maturation efficiency of this over-produced rRNA, and both the number and the efficiency of ribosomes in protein synthesis are also decreased. Hence, regulation in the post-transcriptional processes accounts for the similar protein production per genome in these two cycles.