Plant Biol (Stuttg) 2003; 5(3): 290-296
DOI: 10.1055/s-2003-40793
Original Paper

Georg Thieme Verlag Stuttgart · New York

The Pollen Tube Pathway in Tasmannia insipida (Winteraceae): Homology of the Male Gametophyte Conduction Tissue in Angiosperms

D. Frame 1
  • 1University Herbaria, University of California, Berkeley, 1001 Valley Life Science Building #2465, Berkeley, CA 94720-2465, USA
  • , Present address: Herbarium, Institut de Botanique, Montpellier, France
Further Information

Publication History

Publication Date:
22 July 2003 (online)

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Abstract

The pathway of the pollen tube in Tasmannia insipida (Winteraceae), an archaic angiosperm, is described. Visual observations and measurements of percentage sugar content from stigmatic exudate and the calyptra droplet were made. The droplet that forms on the calyptra of unopened flowers was artificially pollinated, but no pollen tubes appeared to grow through it to the gynoecium of female flowers. Calyptra droplets occur on both female and male (having reduced female structures) flowers of this dioecious plant. It is considered unlikely that a drop pollination mechanism, analogous to that found in some gymnosperms, is at work in T. insipida, and it is proposed that one possible droplet function is as a “reward” to potential pollinators in advance of flower opening. Pollen tubes were observed to grow almost exclusively along epidermal cells. Early thoughts on angiosperm transmission tissue are re-examined and built upon. It is proposed that the male gametophyte conduction tissue in angiosperms is homologous with epidermal tissue, and that pollen tube passage occurred originally solely along the surface of specialized epidermal cells, or possibly for short distances along unspecialized regions covered with exudate derived from these cells. Some earlier attempts to explain transmitting tissue homology and evolution are discussed.

References

D. Frame

Herbarium
Institut de Botanique

163 rue A. Broussonnet

34090 Montpellier

France

Email: aurora@isem.univ-montp2.fr

Section Editor: G. Gottsberger