The role of the exine coating in pollen–stigma interactions in Brassica oleracea L

Abstract

SUMMARYWhen the dehydrated pollen grain of Brassica oleracea L. alights on a receptive stigma the pollen coat flows out from the exine to form an appresoria-like ' foot' and, within a matter of some 30 min, gross ultrastructural changes become visible both within the protoplast and in the foot itself. These changes are interpreted as reflecting the limited movement of water, and presumably other materials, from the stigma to the grain. The compatible pollen grain then continues to take up water, whilst undergoing other cytoplasmic changes and eventually producing the pollen tube. The tube grows from the colpus towards the point of contact with the stigma, beneath which the outer layer of the papillar wall has become more loosely packed. The pollen tube enters the wall at this point and, as a consequence of its rapid extension, the grain is frequently lifted away from the papilla. The tube then grows between two layers of the pectocellulosic papillar wall into the stigmatic parenchyma, where it follows an intercellular route. These events are discussed in terms of current views of the relationship between male and female cells at these early stages of the pollen stigma interaction.

Expression of a polygalacturonase enzyme in germinating pollen of Brassica napus

“…The location of the enzyme in pollen tubes in contact with papillar walls suggests that the PG enzyme is involved with the papillar wall modifications observed during pollination in this genus (Elleman and Dickinson 1990;Elleman et al 1992;Dearnaley et al 1999). As the enzyme belongs to the exo-PG family (Robert et al 1993) it possibly degrades the polygalacturonate end chains of the pectin of stigma cell walls.…”

“…A number of studies have shown that tube penetration is accompanied by cell wall "expansion" or "loosening" (Elleman et al 1988(Elleman et al , 1992Elleman and Dickinson 1990, Kandasamy et al 1994, Dearnaley et al 1999. These changes to the architecture of the papillar cell wall, which presumably facilitate successful passage of the pollen tube, may be related to the release of wall modifying enzymes from the stigma cell (Elleman and Dickinson 1996) or from the approaching pollen tube (Dearnaley et al 1999).…”

Characterization of anther‐expressed genes encoding a major class of extracellular oleosin‐like proteins in the pollen coat of Brassicaceae†

“…It is known that tryphine undergoes structural changes during pollen desiccation, which renders it more or less impermeable to water. Following the initial contact between the pollen grain and the stigmatic surface of species with dry stigmas, for example, B. napus, A. thaliana, the tryphine begins to flow out from the pollen grain to form a contact zone, through which hydration of the pollen must occur (Elleman and Dickinson, 1990). During this process, the tryphine undergoes a radical reorganization of its structure, known as coat conversion, with the formation of numerous vesicles or lipidic droplets and membrane-like structures (Dickinson, 1995;Elleman and Dickinson, 1986).…”

Characterization of Oleosins in the Pollen Coat of Brassica oleracea

“…Safe carriage of this information from the anther to a receptive stigma Is ascertained by a thick wall around the pollen grain. In many species, the outermost layer of this wall is a lipidic coating, containing proteins and carbohydrates, that is well suited to protect the poilen pro toplast and to mediate pollen transport, but it is also equipped to play a role in pollen-stigma interactions (HesiopHarrison, 1979;Knox, 1984;Elleman and Dickinson, 1990;Elleman et a!., 1992;Dickinson, 1993;Doughty etal., 1993).…”