Sporoderm ontogeny in Chamaedorea microspadix (Arecaceae): self-assembly as the underlying cause of development

Abstract

The developmental events in the periplasmic space and cytoplasm of microspores of Chamaedorea microspadix during sporoderm ontogeny have been traced in detail from cytokinesis and early tetrad stage to the formation of intine in mature two-celled pollen grains. Several pre-pattern structures as seen in the periplasmic space of early microspores (dark-contrasted globules, ribbon-like striped structures, strings of beads, spherical units, radially oriented columns of spherical units, rod-like units), can easily be read as different types of micelles (spherical, cylindrical micelles, so-called segmented worms) and their intermediate forms (strings, perforated filaments, columns of spherical micelles). Funnel-like procolumellae, arranged as complexes of bent units, appear next at the middle tetrad stage. These “funnels” possibly correspond to double gyroid phase, typical for a diblock copolymer system, adapted to constraints of the narrow periplasmic space. The foot layer and few endexine lamellae with central white lines appear as laminate (“neat”) micelles, with typical gaps between the laminae; they emerge through intermediate forms of micelles as strings of spherical micelles and/or perforated laminae. Strings are probably a preferential intermediate form of micelle formation in the course of exine development in Chamaedorea: they emerge at every ontogenetic step and participate in the appearance of every exine layer. The first (channelled) layer of the two-layered intine beneath the aperture appears probably on the base of cylindrical micelles. The sequence of the sporoderm layer formation can be understood as a sequence of self-assembling mesophases (and their intermediate forms) in the colloidal system of the microspore periplasmic space, unfolding through the ontogenetic time.