THE ROLE OF SELF-ASSEMBLY IN BIOLOGICAL-SYSTEMS - EVIDENCE FROM IRIDESCENT COLLOIDAL SPOROPOLLENIN IN SELAGINELLA MEGASPORE WALLS

Iridescent exines have previously been reported in both fossil and mod ern megaspores of selaginellalean affinity. This striking feature has been shown to result from a colloidal crystal configuration of the exi ne units in at least part of the wall. This paper discusses the mechan ics of formation of the colloidal crystal and of the adjacent wall lay ers (by depletion attraction), and provides a detailed explanation of the cause of the iridescence. Selaginella leaves and virus aggregates provide comparisons with the iridescent arrangement present in the spo re wall. The self-assembly aspect of colloidal structures in biologica l systems is explored. Periods of self-assembly in organismal developm ent may represent a saving in terms of stored information retrieval. S elf-assembly, and its often chaotic behaviour, offer the prospect of l arge changes in organismal construction associated with relatively lit tle change in the underlying genetic configuration.