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Abstract Detail


Developmental and Structural Section

Williams, Joseph H. [1].

Developmental evolution of the progamic phase: Amborella trichopoda (Amborellaceae).

Early angiosperms are hypothesized to have had rapid reproduction relative to their gymnosperm-like ancestors, and acceleration of the progamic phase - the life history stage between pollination and fertilization - is thought to have been a major component of this heterochronic transition. I studied structural aspects of the pollen tube pathway and the timing of pollen tube growth and fertilization in Amborella trichopoda (Amborellaceae), based on hand pollinations in the field in New Caledonia. When the stigma was first receptive, the Amborella female gametophyte was near structural maturity. Pollen germination began within two hours after pollination (hap) and pollen tubes were first seen entering the female gametophyte 24 hap. After pollen germination pollen tubes with callose plugs grew in secretions between multicellular stigmatic hairs; then entered the carpel via the narrow secretion-filled ventral slit, which forms the semi-open transmitting tract; and then grew around the orthotropous carpel within the ovarian cavity to the micropyle. Hundreds of pollen tubes grew to the base of the stigma but then arrested or reversed direction. By far, the greatest reduction in the pollen tube cohort occurred within the stigma (on average only 1.96 pollen tubes ever entered the transmitting tract), suggesting the importance of this novel angiosperm feature in mediating pre-zygotic selection on pollen tubes. The Amborella fertilization interval is typical of phylogenetically derived angiosperms (ca. 24 hours long), but in contrast to many of these it is achieved via a slow pollen tube growth rate (max ca. 120 µm/hr) and a short pollen tube pathway (ca. 1-2 mm long). Amborella and other basal angiosperms have dramatically accelerated pollen germination and pollen tube growth rates relative to gymnosperms, but they did not exploit the tremendous diversity of developmental niches characterized by further lengthening of the pollen tube pathway and/or modification of the fertilization interval.


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Related Links:
Williams lab website


1 - University of Tennessee, Department of Ecology and Evolutionary Biology, 442 Hesler Biology, Knoxville, Tennesee, 37996, USA

Keywords:
fertilization
Amborella
pollen tube growth
Basal angiosperms
heterochrony
stigma
progamic phase.

Presentation Type: Oral Paper:Papers for Sections
Session: CP26
Location: Boulevard C/Hilton
Date: Tuesday, July 10th, 2007
Time: 12:00 PM
Number: CP26015
Abstract ID:1466


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