Observations on the experimental destruction and substructural organisation of the pollen wall of some selected Gymnosperms and Angiosperms

Abstract

Degradation of mature pollen walls by treatment with potassium permanganate was undertaken in Lavatera arborea (Malvaceae), Oenothera speciosa (Onagraceae) and Stangeria eriopus (Stangeriaceae) in order to investigate the substructural organisation of their exines. In Lavatera arborea the cores of the columellae are eroded so that they appear as hollow tubes and radially oriented rod-like elements (tufts) are revealed in the ectexine and endexine. An oxidative treatment with glacial acetic acid revealed clusters of darkly contrasted Sporopollenin Acceptor Particles (SAPs) along the surface of the columellae. This indicates that the cores of the columellae are formed independently of SAPs, whereas the sporopollenin in the outer parts of the columellae is receptor-dependent and is much more resistant to oxidation. After oxidative treatment of Oenothera pollen only the outlines of the three layers – of tectum, columellae and endexine, represented by the boundary layer, are visible, together with a complex system of tuft-tubules. The binder elements of tufts and the boundary layer of all exine strata are resistant to degradation and are interpreted as containing sporopollenin laid down on SAPs rather than the receptor-independent material of the remainding exine. Oxidative treatment of the alveolate exine of Stangeria eriopus results in progressive erosion with the duration of treatment. The binder zones of tufts and the tectal part of the exine, which are the walls of the alveolae and also their boundary layer, are the most resistant to oxidation and correspond to SAPs. The core subunits of tufts, that is the central parts of the alveolae, do not resist oxidation and are interpreted as sites of receptor-independent sporopollenin. Thus, in spite of the very different exine structure in Lavatera arborea, Stangeria eriopus and Oenothera speciosa, the exines of these species, on the substructural level, react to oxidative treatment in a similar way. We conclude that the alternative models of exine substructure proposed by various authors differ mainly in terminology rather than in substance.