Abstract
Pollen grains of flowering plants display a fascinating diversity of forms. The observed diversity is determined by the developmental mechanisms involved in the establishment of pollen morphological features. Pollen grains are generally surrounded by an extremely resistant wall displaying apertures that play a key role in reproduction, being the places at which pollen tube growth is initiated. Aperture number, structure, and position (collectively termed ‘aperture pattern’) are determined during microsporogenesis, which is the earliest step of pollen ontogeny. Here, we review current knowledge about aperture pattern developmental mechanisms and adaptive significance with respect to plant reproduction and how advances in these fields shed light on our understanding of aperture pattern evolution in angiosperms.
Highlights
IntroductionThe male gametophytes of flowering plants, are simple organisms composed of two to three cells surrounded by a complex multilayered protective wall made of sporopollenin (outer wall, called exine), and cellulose and pectins (inner wall, called intine)
Pollen grains, the male gametophytes of flowering plants, are simple organisms composed of two to three cells surrounded by a complex multilayered protective wall made of sporopollenin, and cellulose and pectins
The aperture pattern results from a combination of two developmental processes: one that concerns the formation of each individual aperture and the other one that determines the position and number of apertures on the pollen surface
Summary
The male gametophytes of flowering plants, are simple organisms composed of two to three cells surrounded by a complex multilayered protective wall made of sporopollenin (outer wall, called exine), and cellulose and pectins (inner wall, called intine). Apertures may vary in structure (pore, furrow, or both), number (from no aperture to more than one hundred), and position on pollen surface. They are flexible and permeable areas preventing pollen wall breakage during volume variation due to water flows, and they allow gas exchanges and are thereby strongly involved throughout the processes of fertilization, from pollen survival during pollination to germination of the pollen tube [2]. The aperture pattern results from a combination of two developmental processes: one that concerns the formation of each individual aperture (structural features of the pollen wall) and the other one that determines the position and number of apertures on the pollen surface (architectural features). Selection and constraints may act on either or both developmental processes and on the result of these developmental processes, i.e., on pollen grain morphology
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