Simulation of exine patterns by self-assembly

New experimental modeling of exine has been undertaken to verify general ideas on the participation of self-assembly processes in sporoderm development. Our aim was to confirm our hypothesis that a considerable part of the developmental processes is the unfolding sequence of self-assembling micelle mesophases and their aggregates in the colloidal system of the microspore periplasmic space. Strong support for this hypothesis would be experimental modeling of sporoderm-like patterns in vitro. We used surface-active substances for the preparation of colloidal mixtures: glycoproteins, lipopolysaccharides and natural sporopollenin precursors-phenolics and fatty acids. In vitro conditions, when the influence of the genome is absent, a number of patterns, mimicking separate layers of sporoderm-ectexine, endexine and supratectal ornamentations-at different development stages have been obtained and studied with TEM. Simulations, appearing as scattered and clustered spherical micelles and columns of spherical micelles mimic sporoderm development at young tetrad stages in most species. A layer of semi-fused spherical micelles, transient to cylindrical micelles, simulates the columellate primexine at the middle tetrad stage. The simulation with laminate micelles mimics endexine lamellae with central white lines. More complex simulations such as spongy, perforated and stalactite-like patterns, mimicking exine layers of some basal and advanced angiosperms and extinct gymnosperms, were also obtained. Some simulations bear spine-like and gemma-like structures on the surface, mimicking ornamentation of natural sporoderm. Our results show that a considerable part of the development of the exine takes place through self-assembly.