Pollen development of Rondeletia odorata (Rubiaceae).
Pollen wall ontogeny of RONDELETIA: odorata was studied with transmission electron microscopy (TEM) and scanning electron microscopy (SEM) from tetrad stage until maturity. The ontogenetic sequence of wall development in RONDELETIA: follows, to some extent, the basic scheme in the angiosperms, i.e., development starts centripetally with the pro-columellae in a plasmalemma surface coating (primexine) at the early tetrad stage when the microspores are still enveloped by callose, until intine formation in young pollen grains. The main ontogenetical features of Rondeletia odorata pollen are (1) the very thin irregular foot layer, (2) development of a continuous layer of radially oriented membranous granular material under the thick endexine, (3) initiation of intine before first mitosis with characteristic radial plasmalemma invaginations, and (4) a strong stretching force upon engorgement just prior to dehiscence, which leads to reduction in thickness of all wall layers. The possible function of Golgi vesicles in the considerable increase in surface area of the plasmalemma at intine initiation is discussed. The endocingulum observed on acetolyzed and sectioned mature grains is explained ultrastructurally.
El-Ghazaly
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Palynological Laboratory, Swedish Museum of Natural History, Roslagsvägen 101, S-104 05 Stockholm, Sweden. Laboratory of Plant Systematics, Institute of Botany and Microbiology, K.U.Leuven, Kard. Mercierlaan 92, B-3001 Heverlee, Belgium.
Huysmans
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Smets
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