Artificial pollen walls simulated by the tandem processes of phase separation and self‐assemblyin vitro

Abstract

Despite numerous attempts to elucidate the developmental mechanisms responsible for the observed diversity of pollen and spore walls, the processes involved remained obscure until the structures observed during exine development were recognized as a sequence of selfassembling micellar mesophases. To confirm this, a series of in vitro experiments was undertaken in which exine-like patterns were generated in colloidal mixtures by self-assembly, without any genomic participation. The intention was to test whether all the main types of exine structure could be simulated experimentally.Mixtures of substances, analogous to those involved in microspore development, were left undisturbed while water evaporated and self-assembly occurred. We varied the substances, their combinations and concentrations, and the physical constraints to make the experiments closer to the situation in nature. The resulting dry films were then examined using transmission electron microscopy.A variety of microstructures, simulating the full range of exine types, was obtained by micellar self-assembly. Moreover, the signs of related physicochemical process (i.e. phase separation) were also observed.Simple, energy-efficient, physical-chemical interactions, phase separation and self-assembly, are capable of generating exine-like patterns, providing evidence that these processes share control of exine formation with the well-documented program of gene expression.

The Role of Cutinsomes in Plant Cuticle Formation

“…The process of these suberinsomes’ in vitro formation resembles that of cutinsome creation. It is also worth noting that self-assembly processes were also implicated in exine development in more than 30 plant species from a wide variety of taxa [ 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 ]. Moreover, GELP77 , a GDSL-type esterase/lipase gene that is mainly expressed in Arabidopsis microspores and tapetal cells [ 106 ] at early stages of flower development [ 107 ], has recently been shown to participate in pollen wall development and has been suggested to play a similar function in pollen to that of CUS1 in S. lycopersicum fruit cuticle [ 106 ].…”

An integral insight into pollen wall development: involvement of physical processes in exine ontogeny inCalycanthus floridusL., with an experimental approach

“…We have thus confirmed our hypothesis (Gabarayeva et al ., 2019b), and have developed it by demonstrating the unity of the two physicochemical processes (phase separation and self‐assembly) involved in exine development as an underlying mechanism working without genomic control.…”

“…As shown in our many ontogenetic studies (e.g. see references in Gabarayeva et al ., 2019b), the regular and recurrent structures observed in exine development, even in remote species, are as regular and geometrically structured as micellar mesophases. Hence, it was logical to suppose that these two processes – phase separation and self‐assembly – are coupled in some way.…”

“…Hence, it was logical to suppose that these two processes – phase separation and self‐assembly – are coupled in some way. In our joint work, we hypothesized that both processes worked in tandem (Gabarayeva et al ., 2019b). We have demanstrated such cooperation, illustrating patterns similarity between some micellar mesophases and some exine developmental stages in the ontogeny of one or another plant species.…”

“…Currently, our aim is to show this ‘work in tandem’ through the whole exine development of a single species, C. floridus , as an indivisible and continuous process. It would be helpful to restate this hypothesis (Gabarayeva et al ., 2019b) and to develop it by showing the unity of the two processes (phase separation and self‐assembly) involved in exine development.…”