Pollen wall development in Lupinus polyphyllus: Looking for underlying mechanisms, with in vitro simulation of exine

Abstract

It was suggested that physicochemical processes, self-assembly and phase separation, are the hidden side of pollen wall formation. A new look at the developmental palynology as to “work-in-tandem” of well-known gene expression and underappreciated physical regularities allows a deeper understanding of exine development. The sequence of the developmental stages in Lupinus exine has been analyzed based on the above idea. To check the above idea, a modeling of exine-like pattern was carried out in vitro with colloidal mixtures of surfactants, analogous to those in natural anther. Flower buds of different size were collected from the Garden of the Komarov Botanical Institute, St. Petersburg, for several seasons. After fixation of the Lupinus material, sections were prepared and examined with TEM and SEM. For modeling exine development in vitro, our own method was used to obtain simulations. The successive developmental structures observed within the microspore periplasmic space have occurred to be the same as in the typical micellar self-assembly sequence in colloidal system of surfactants. Simultaneously, signs of phase separation in the fluid of the periplasmic space were evident. As was expected, several exine-like simulations of the Lupinus exine structures were obtained in our experiments. Pure physicochemical processes are capable to build exine-like patterns. Hence, physical processes share influence on exine development with genome. This confirms a value of interdisciplinary approach in the field of developmental biology.