Sporoderm development in Trevesia burckii (Araliaceae). I. Tetrad period: Further evidence for the participation of self-assembly processes

The developmental events in the periplasmic space and cytoplasm of microspores, and in the tapetum of Trevesia burckii during the tetrad period have been traced in detail during microspore ontogeny from the sporogenous cell stage to the late tetrad stage and the initiation of the foot layer. The data obtained provide support to two of our previously proposed hypotheses: (1) the glycocalyx (scaffolding primexine matrix) is a colloidal system; (2) the involvement of processes of self-assembly of a number of colloidal micellar systems to the exine development. The main structures of the reticulate ectexine up to the establishment of the foot layer are columellae and tectum which evidently form on a base of spherical and cylindrical transitive micelle mesophases after sporopollenin accumulation. The importance of the callose envelope surrounding microspores for exine development is discussed in the light of recent findings. Two possible pathways of pattern determination are possible. One suggests the role of the plasma membrane in pattern imprinting and the corresponding necessity of the transfer of 2-D information to 3-D. Our current supposition is that the other, self-assembly physical phenomena, cellular tensegrity, also participate in the process of the establishment of a wide-spread reticulate exine pattern which appears as the result of an interplay of the microspore cytoskeletal prestress and the resistance from the ECM (exocellular matrix = glycocalyx) adhesive sites. More and more information is appearing that provides evidence for the importance of mechanical forces and physico-chemical regularities in the living world.