At the free microspore stage, a material with a similar electron density to sporopollenin
fills the whole locule and deposits over the pollen grain wall.
1989, Lewis 1991), beneath which, is a thin sporopollenin
The cell may enter a quiescent state during which its covering becomes thicker and accumulates materials similar, at least in terms of their resistance, to the sporopollenin
of the walls of pollen grains and other plant spores.
On the other hand, the dense layer of Heterocapsa niei and other dinoflagellates has been suggested to contain sporopollenin
, a very resistant plant terpenoid that has been demonstrated to be insoluble, even in hot ethanolamine (Loeblich, 1970; Morrill and Loeblich, 1981).
Ubisch bodies, (1) con-peito grains) are a-cellular structures of sporopollenin
that might occur on the inner tangential and radial walls of tapetal cells.
* its component sporopollenin
is as effective as cholestyramin in binding neurotoxins and more effective in binding toxic metals then any other natural substance found;
The four cells resulting from meiosis/cytokinesis become a tetrad of spores, each encased in a heavy sporopollenin
wall, the sporoderm.
Orbicules are tiny sporopollenin
particles up to 3-4 [micro]m in
The tapetum and the microspores contain homologous, nearly identical genetic information for the production, release, and accumulation of sporopollenin
(Hesse, 1986; Pacini et al., 1985; Young et al., 1979).
Considering a possible ancestral form, perhaps represented by Coleochaete, loss of spore motility (flagellar reduction and loss) and development of a protective spore wall (with sporopollenin
) probably occurred quite early in the process of land-plant adaptation (cf.
Thus it is uncertain whether it is composed of sporopollenin
, like those in the Asclepiadoideae, or of elastoviscin, which Dannenbaum and Schill (1991) found covering the tetrads in Raphionacme (P eriplocoideae).
The secretory tapetum is composed of cells usually with large nuclei [ILLUSTRATION FOR FIGURES 1, 64, 67 OMITTED], and it stains dark due to the cytoplasmic contents of lipids, proteins, and sporopollenin
precursors [ILLUSTRATION FOR FIGURES 4, 5, 38, 42, 45, 47-50, 54, 62, 63, 65, 66 OMITTED].