Comparative Pollen Development in Dioscoreales

Abstract

Pollen and orbicule ontogeny in representatives of three genera of Dioscoreales-Narthecium ossifragum Huds. (Nartheciaceae), Tacca artocarpifolia Seem. and Tacca chantrieri André (Dioscoreaceae), and Dioscorea communis (L.) Caddick & Wilkin (Dioscoreaceae)-is described and illustrated using LM, SEM, and TEM. The main difference is in microsporogenesis, which is successive in Narthecium Huds. and simultaneous in Tacca J.R. & G. Forst. and Dioscorea L. This is reflected in the tetrad configuration but not in the apertures: Narthecium and Tacca are monosulcate, while Dioscorea has two equatorial apertures. Other features of pollen development are similar in all three genera. Exine development starts at the proximal pole, and during the tetrad stage, the exine remains thicker at this pole. Intine development begins before mitosis. A conspicuously channeled intine forms beneath the aperture(s) in all three genera, and in Tacca it also occurs in nonapertural regions. After mitosis, the generative cell is situated at the proximal pole in all genera. Orbicules are present in Narthecium and Dioscorea but not in Tacca, although it has a secretory tapetum. In the tetrad stage, pro-orbicules appear on the tapetum in Narthecium and Dioscorea, and pro-sporopollenin is consequently deposited to form the orbicule wall.

The Relationship between Tapetum Cells and Microspores Based on Protein Localization inFraxinus angustifolia(Oleaceae) Pollen Grains

“…At the bicellular stage, the sporopollenin appeared polymerized, and the ectexine and endexine layers were well differentiated, as also happens in other taxa (Rowley and Dahl 1977;Suárez-Cervera et al 1995). At this stage, the intine deposition had finished, showing the characteristic intine channels similar to those described in the apertural region of other mature pollen grains (Suárez-Cervera et al 2000;Schols et al 2005).…”

Misinterpretations in Palynology

“…3 in "Methods in Palynology"). Examples for taxa with disulcate pollen are the monocots Tofieldia calyculata with one sulcus distally, the other proximally, Uvularia grandiflora, Eichhornia crassipes (Hesse et al 2009), some Dioscorea species (Schols et al 2005), Pontederia cordata (Halbritter 2016), Calla palustris (Ulrich et al 2013), and the magnoliid Calycanthus floridus (Huynh 1976).…”