Exine development: the importance of looking through a colloid chemistry ``window'

Most biological construction systems operate within the colloidal dimension. In view of this, it seems reasonable to reassess what is known of the early stages of exine development in the light of a brief excursion into colloid and micelle behaviour. The results of this analysis show remarkable similarity of structures and suggest that almost all of the features seen during early pollen wall development can be easily interpreted using simple, established colloidal principles. This study of exine framework and endexine development offers the possibility that growth of the early exine progresses by successive transitory mesophases of a constrained micellar system. The self-assembling micelle mesophases will all be clearly recognized as constituents of the developing exine. They include spherical, cylindrical, continuous layers of hexagonally-packed cylindrical units and lamellar mesophases which most probably correspond to future granules, columellae, complex columellar (and alveolar) microarchitecture and ``white-line-centred' lamellae. Furthermore, the various types of micelle involved have the potential to perform the functions previously loosely assigned to the exine.