Developmental and Structural Section
Taylor, Mackenzie , Osborn, Jeffrey .
Pollen development and pollen tube growth in Victoria (Nymphaeales).
The giant waterlily Victoria comprises two species, Victoria amazonica and V. cruziana. Both species are native to South America but can be found in cultivation along with several hybrids, including 'Longwood' hybrid. Victoria is nested within Nymphaeaceae, and the genus is typically hypothesized to be sister to the east Asian genus Euryale, with the Victoria-Euryale clade sister to Nymphaea. However, recent phylogenetic analyses have revealed uncertainty in the relationships among the 'core' Nymphaeaceae. Water lilies (Nymphaeales) comprise one of the oldest independent lineages of angiosperms, diverging from the basal-most, or second-most basal node of the angiosperm phylogenetic tree. Because of their early origin and relatively long independent evolutionary history, water lilies are important for understanding early angiosperm evolution. Victoria is of particular interest because it exhibits several reproductive characters that are likely derived within Nymphaeales, including very large,thermogenic flowers, pollination via beetle entrapment, and an annual life-history.The evolution of these derived floral and life-history traits may have had consequences for other aspects of reproductive development in Victoria, including microspore and microgametophyte development. The objective of this study was to characterize pollen and early pollen tube development in Victoria.To investigate pollen development, anthers from both species and 'Longwood' hybrid were dissected from developing floral buds and studied using combined light,scanning electron, and transmission electron microscopy. Pollen morphology and ultrastructure were documented, as well as timing of pollen wall development and tapetal dissociation. Formation of the exine in Victoria was initiated in the tetrad stage. Following meiosis, microsporesare fully separated by callose within the tetrad, but as the callose breaks down, the tectal layers of adjacent microspores fuse. At initial fusion points,the infratectal layers become continuous. The calymmate tetrad in Victoria is a larger dispersal unit than the microspore alone, and it provides four opportunities for germination per dispersal event. Each constituent pollen grain has a ring-like aperture. The exine in Victoria is tectate-columellate and is traversed by thin microchannels; the endexine is lamellate. The tapetum is secretory, but it physically protrudes into the anther locule during ontogeny. To investigate pollen development after pollination, flowers were hand-pollinated. Carpels were collected at 15 min intervals for 1 h after pollination and observed with fluorescence microscopy to document developing pollen tubes. Pollen germination and pollen tube traits will be discussed, as will the functional correlations between pollen characters and pollination biology in Victoria.
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1 - Creighton University, Department Of Biology, 2500 California Plaza, Omaha, NE, 68178, USA
2 - The College Of New Jersey, School Of Science, 2000 Pennington Road, P.O. Box 7718, Ewing, NJ, 08628-0718, USA
pollen tube growth
Presentation Type: Oral Paper:Papers for Sections
Location: Union D/Hyatt
Date: Monday, July 9th, 2012
Time: 3:45 PM