Sporoderm development inSwida alba(Cornaceae), interpreted as a self-assembling colloidal system

The developmental events in microspores and the tapetum in Swida alba have been traced in detail. The first elements of the glycoprotein glycocalyx appear as hemispherical, elongated, and conical units, rooted in surrounding callose layer. These units are evidently transitional forms of spherical micelles. At the middle tetrad stage, these units (future columellae) acquire a cylindrical form and consist of clusters of radially oriented subunits (clusters of cylindrical micelles), twined round with a spiral element. At the late tetrad stage, procolumellae increase, and the tectum with microchannels is initiated at the interface of the callose and the glycocalyx layers. Cone-like ‘skeletons’ – typical crystal-like structures – of the future spines emerge on the tops of the columellae, and the primordial white-lined lamella appears as a demarcation line between the future foot layer and endexine. During disintegration of the tetrads, several new white-lined lamellae arise that are evidently formed on the base of laminate micelles with their typical gaps seen in transmission electron microscopy as white lines. After addition of the second granular layer of endexine, all the elements of exine become thick as a result of sporopollenin accumulation. The completion of sporoderm development is carried out after microspore mitosis by intine formation.