Amorphophallus: New insights into pollen morphology and the chemical nature of the pollen wall

Abstract

In pollen characters, Amorphophallus is one of the most diverse genera in the Araceae. The present work is a critical survey of contradicting reports on the impact of acetolysis treatment on Amorphophallus pollen, on the chemical nature of the outer pollen wall layer and of electron-dense (dark) granules found within it. Furthermore, we wanted to clarify the pollen polarity and to test conclusions based on different preparation techniques. Pollen morphology of 25 species is investigated by light microscopy, scanning electron microscopy and transmission electron microscopy. Our results show that Amorphophallus pollen is not resistant to acetolysis treatment. The use of different transmission electron microscopy staining methods proved the polysaccharide nature of the outer pollen wall layer and of the granules within it. Moreover, an additional thin surface layer was found in all investigated species. Microspores in early and late tetrad stages show that the less convex side of the microspore is the proximal face and the more convex side the distal face. The extrusion of pollen in strands is illustrated for the first time by light microscopy and scanning electron microscopy. Furthermore, observations of pollen in water showed that in some of the investigated species the pollen wall is shed immediately before pollen tube formation.

Keywords:

• Araceae
• Thomsonieae
• ultrastructure
• staining methods
• polysaccharides
• granules
• tetrads
• pollen strands
• pollen wall shedding

Acknowledgements

The authors wish to thank the Botanical Garden of the University of Vienna, Vienna, Austria, Josef Bogner (Munich Botanical Garden, Munich, Germany) and Wilbert Hetterscheid (Von Gimborn Arboretum, Doorn, The Netherlands) and David Prehsler (University of Vienna, Vienna, Austria) for providing plant material. The authors also wish to thank the reviewers for constructive comments. This work is part of the Araceae project (P20666), funded by the Austrian Science Fund (FWF).

Disclosure statement

No potential conflict of interest was reported by the authors.

Specimens investigated

Amorphophallus asterostigmatus Bogner et Hett. Bogner J., HBV, cult. (ARA130292, M 2096).

Amorphophallus atrorubens Hett. et Sizemore. (Hetterscheid H.AM. 737).

Amorphophallus bulbifer Blume. HBV, cult. (ARA120233).

Amorphophallus henryi N.E.Br. HBV, cult. (ARA110214).

Amorphophallus interruptus Engl. et Gehrm. Hetterscheid W., HBV, cult. (ARA120234).

Amorphophallus konjac K.Koch, Koch R. HBV, cult. (ARA060119).

Amorphophallus krausei Engl. HBV, cult. (ARA090136).

Amorphophallus lacourii Linden et André. comb. nov. Basionym: Pseudodracontium lacourii N. E. Br., Bogner J. (M 2640).

Amorphophallus latifolius (Serebryanyi) Hett. et Claudel. comb. nov. Basionym: Pseudodracontium latifolium Serebryanyi, Hetterscheid W., HBV, cult. (ARA090177).

Amorphophallus longituberosus Engl. et Gehrm. Hetterscheid W. (Hetterscheid H.AM. 1252).

Amorphophallus mangelsdorffii Bogner. Mangelsdorff R. (M 550).

Amorphophallus mossambicensis (Schott ex Garcke) N.E.Br. Hetterscheid W. (Hetterscheid H.AM.0447).

Amorphophallus myosuroides Hett. et A. Galloway. Prehsler D., HBV, cult. (ARA120236)

Amorphophallus ongsakulii Hett. et A. Galloway. Prehsler D., HBV, cult. (ARA120237).

Amorphophallus operculatus Hett. et Sizemore. Prehsler D., HBV, cult. (ARA120262).

Amorphophallus paeoniifolius (Dennst.) Nicolson. Bogner J. (M 1280).

Amorphophallus palawanensis Bogner et Hett. Hetterscheid, W. (Hetterscheid HAM. 124).

Amorphophallus polyanthus Hett. et Sizemore. HBV, cult. (ARA110215).

Amorphophallus prainii Hook.f. Bogner J. (M 2661).

Amorphophallus rhizomatosus Hett. Bogner J. (M 2305).

Amorphophallus sumawongii (Bogner) Bogner et Mayo. Bogner J. (M 372).

Amorphophallus serrulatus Hett. et A. Galloway. Prehsler D., HBV, cult. (ARA130293).

Amorphophallus stuhlmannii (Engl.) Engl. et Gehrm. HBV, cult. (ARA110216).

Amorphophallus taurostigma Ittenb., Hett. et Bogner. Madagascar, north of Morondava, near Baobab alley, coastal forest, near the street, 20° 12ʹ 27ʺ S, 44° 22ʹ 5ʺ E, (M 4689), Sieder A., Knirsch W., Berg Ch. & Pinter M. HBV, cult. (WU).

Amorphophallus yunnanensis Engl. HBV, cult. (ARA 090135).