The Role of Physical Processes in Pollen Wall Morphogenesis: Hypothesis and Experimental Confirmation

Abstract

The review is devoted to the analysis and generalization of modern knowledge about the mechanisms underlying the ontogeny of the male gametophyte envelope. New and earlier data on exine development аre discussed, and recurrent phases in the development of exine of phylogenetically distant plant species are emphasized. Though exine formation has been shown to be dependent on plenty of genes, the reiteration of exine patterns in different plant species (e.g. columellate, granular, “white-lined” lamellae) suggests that these patterns are based on some non-biological principles of space-filling operations. However, mechanisms involved remained obscure until it became clear that the sequence of structures observed during exine development coincided with the sequence of self-assembling micellar mesophases. It was discovered later that another physical-chemical process—phase separation—participated in exine formation. To confirm that exine-like patterns are capable of generating in vitro by simple physical processes, and their formation does not require regulation at the genome level, some our and other authors’ in vitro experiments were undertaken; the data obtained are discussed. Several series of our new experiments on modeling exine development with mixtures of surface-active substances resulted in some patterns simulating the main types of natural exine. Transmission electron microscopy analysis of the samples has shown that patterns simulating the full range of exine types were obtained by joint action of phase separation and micellar self-assembly. The reconsideration and analysis of our and other authors’ morphogenetic and modeling data revealed that molecular-genetic mechanisms and physical forces work in tandem, with considerable input of physical processes.