Development of sterile ovules on bisexual cones of Gnetum gnemon (Gnetaceae)

Citation
Cj. Haycraft et Js. Carmichael, Development of sterile ovules on bisexual cones of Gnetum gnemon (Gnetaceae), AM J BOTANY, 88(7), 2001, pp. 1326-1330
Citations number
23
Categorie Soggetti
Plant Sciences
Journal title
AMERICAN JOURNAL OF BOTANY
ISSN journal
00029122 → ACNP
Volume
88
Issue
7
Year of publication
2001
Pages
1326 - 1330
Database
ISI
SICI code
0002-9122(200107)88:7<1326:DOSOOB>2.0.ZU;2-A
Abstract
Angiosperms and Gnetales (Ephedra, Gnetum, Welwitschia) represent the only seed plants that regularly produce bisexual cones. Unfortunately, the ferti lity and function of ovules formed on bisexual cones of Gnetales have remai ned unclear. Some reports indicate that the ovules are sterile while others indicate that they may develop into seeds. This study demonstrates three d ifferent developmental patterns of ovules formed on bisexual cones of Gnetu m gnemon. Type I ovules did not develop at all after pollination and repres ented the majority of ovules on each cone. Type IT ovules enlarged slightly after pollination due to the enlargement of nucellar tissue. Type LII ovul es were typically found on the terminal whorl and developed into seed-like structures. The enlargement was due to proliferation of megagametophyte tis sue. Sectioned material revealed that megagametophytes show altered develop ment compared to those found in functional female ovules. None of the ovule s studied contained embryos, and thus all were sterile. Densitometry of 4 ' ,6-diamidino-2-phenylindole (DAPI)- stained sections revealed that megagam etophyte nuclei formed in the sterile ovules are unreduced (diploid) and th us do not form viable female gametes.