POSITION-DEPENDENT CONTROL OF CELL FATE IN THE FUCUS EMBRYO - ROLE OFINTERCELLULAR COMMUNICATION

The early embryo of the brown alga Fucus comprises two cell types, i.e . rhizoid and thallus which are morphogically and cytologically distin guishable. Previous work has pointed to the cell wall as a source of p osition-dependent information required for polarisation and fate deter mination in the zygote and 2-celled embryo, In this study we have anal ysed the mechanism(s) of cell fate control and pattern formation at la ter embryonic stages using a combination of laser microsurgery and mic roinjection. The results indicate that the cell wall is required for m aintenance of pre-existing polarity in isolated intact cells, However, all cell types ultimately have the capacity to re-differentiate or re generate rhizoid cells in response to ablation of neighbouring cells. This regeneration is regulated in a position-dependent manner and is s trongly influenced by intercellular communication, probably involving transport or diffusion of inhibitory signals which appear to be essent ial for regulation of cell fate decisions. This type of cell-to-cell c ommunication does not involve symplastic transport or direct cell-cell contact inhibition. Apoplastic diffusible gradients appear to be invo lved in pattern formation in the multicellular embryo.