Persistence of cell division phasing in marine phytoplankton in continuous light after entrainment to light: Dark cycles

The cell division patterns of 11 species of marine phytoplankton were analyzed in cultures maintained in a 14: 10 light: dark cycle followed by 3 days of continuous illumination. All species except two diatom clones showed "typical" phased or synchronized division on the light:dark regime, although the timing of division relative to the light: dark cycle was variable. In six of the species, the division rhythm persisted throughout the 3 days of constant light, suggesting endogenous control. In others, it either damped out after 1 day, or, in the case of the two diatoms, was never evident. Persistence in constant conditions appeared to be correlated with growth rate to some extent, but not to taxonomic grouping, or timing of division on light: dark cycles.