Fig. 6. Possible pathways for the control of early development by p34 in Fucus zygotes. (A) P34 positively controls both the entry in S phase and photopolarisation. Inhibition of p34 activity (in black) prevents both events. Alternatively (B), p34 controls the G1/S transition, which itself is required to activate polarisation events. (C) A third possibility is that cell cycle and polarisation belong to two independent pathways, but a checkpoint prevents polarisation when the cell cycle is arrested before S phase.