AOBPreview originally published online on May 20, 2004
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Annals of Botany 94: 43-50, 2004
© 2004 Annals of Botany Company
The Causes of Self-sterility in Natural Populations of the Relictual Angiosperm, Illicium floridanum (Illiciaceae)
1 Department of Botany, University of Toronto, 25 Willcocks Street, Toronto, Ontario, Canada M5S 3B2, 2 Cell and Molecular Biology Department, Tulane University (Uptown), New Orleans, LA 70118, USA and 3 CSIRO Waite Laboratories, PMB 2 Glen Osmond, SA 5064, Australia
* For correspondence. E-mail tsage{at}botany.utoronto.ca
Received: 10 November 2003; Returned for revision: 12 February 2004; Accepted: 5 March 2004. Published electronically: 20 May 2004
• Background and Aims Illicium floridanum, a species belonging to the basal extant angiosperm taxon Illiciaceae, reportedly exhibits self-incompatibility (SI). To date, the site and timing of SI within the carpel of this species remains unidentified. Thus, the objective of this research was to determine the cellular and temporal aspects of SI in I. floridanum.
• Methods Following controlled application of cross- and self-pollen in natural populations of I. floridanum, embryo sac development and temporal aspects of stigma receptivity, as well as pollen tube growth, fertilization, and embryo and endosperm development, were investigated with the aid of light and fluorescence microscopy.
• Key Results Flowers of I. floridanum exhibited complete dichogamy whereby stigmas only supported cross- and self-pollen tube growth prior to anther dehiscence. In contrast to earlier reports of SI in this species, a prezygotic SI resulting in rejection of self-pollen tube growth at the stigma was absent and there were no significant differences between cross- versus self-pollen germination and pollen tube growth within the style and ovary during the first 5 d after pollination. Structural development of the four-celled embryo sac was not differentially influenced by pollen type as noted to occur in other angiosperms with late-acting ovarian SI. The ovule micropyle and embryo sac were penetrated equally by cross- and self-pollen tubes. In addition, there were no statistically significant differences in cross- versus self-fertilization. A resting zygote and multicellular endosperm at a variety of developmental stages was present by 30 d after application of cross- or self-pollen.
• Conclusions In the clear absence of a prezygotic SI that was previously reported to result in differential self-pollen tube growth at the stigma, self- sterility in I. floridanum is likely due to early-acting inbreeding depression, although late-acting post-zygotic ovarian SI cannot be ruled out.
Key words: Illicium floridanum, self-incompatibility, self-sterility, complete dichogamy, early-acting inbreeding depression, Illiciaceae, Austrobaileyales.
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