Mechanisms of pollen wall development in Lysimachia vulgaris.

Abstract

Exine, this complex sporopollenin-containing and highly variable among taxa envelope of the male gametophyte, consists of two layers, ectexine and endexine. We traced in detail the pollen wall development in Lysimachia vulgaris (Primulaceae), with emphasis on driving forces and critical ontogenetic time. By observation on the sequence of the emergent patterns and by analysis of their substructure with TEM, we intended to clarify the obvious and not-obvious ways of exine construction and to find out the common features in pattern development in other representatives in living nature. The ectexine and endexine ontogeny follows the main stages observed in many other species: first, the appearance of microspore plasma membrane invaginations with isotropic contents within, changed later to anisotropic state; then successive appearance of spherical, rod-like, and lamellate units in the periplasmic space. The lamellate endexine appears unusually early in the exine development. All these elements and their aggregations are manifestation of well-known physical phenomena: phase separation and micellar self-assembly. A consideration of similar surface patterns in very remote taxa suggests the participation in their development of some general nature phenomena as the lows of space-filling operations.