Developmental and Structural Section
Taylor, Mackenzie L. , Williams, Joseph H. .
Pollen tube growth patterns in Trithuria species (Hydatellaceae).
Nymphaeales (water lilies) comprises a lineage that diverges from the basal-most or next most basal node of the angiosperm phylogenetic tree. With the origin of the aquatic habit in this ancient lineage, the reproductive cycle became much shortened, particularly the progamic phase (the period between pollination and fertilization). We know little about the nature of post-pollination events in Hydatellaceae, sister to all other water lilies. Trithuria, the lone genus in the family, may represent an extreme in progamic phase modification because of its highly reduced size and shorter overall life history than any other water lily – it is the only basal angiosperm known to possess an annual life cycle. We carried out field studies in Trithuria austinensis and T. submersa in Western Australia in order to characterize the progamic phase, including the pollen tube pathway, time to fertilization, and pollen tube growth rates. Pollen germination is nearly instantaneous in both species. The majority of pollen tube growth occurs along the surface of the stigmatic hair and pollen tubes do not always grow directly to the carpel mouth. Tubes occasionally branch early in development. Once they enter the carpel, tubes grow within a short, secretion-filled canal. Pollen tubes have callose walls and form numerous callose plugs. The pollen tube pathway of T. austinensis is 3.5 times longer than that of T. submersa, which strongly affects time to fertilization. Because both species are wind pollinated, the differences in pollen tube path length may be more related to differences in their breeding systems. Mean pollen tube growth rates of both species are faster than those of other basal angiosperms, but similar to, or even slower, than those of other water lilies. These comparisons suggest that the extremely short pollen tube pathway, along with rapid pollen germination and pollen tube growth, was the primary mechanism for producing a progamic phase that ranks as one of the shortest known among all angiosperms.
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1 - University of Tennessee, Ecology and Evolutionary Biology, Knoxville, TN, 37996, USA
Presentation Type: Oral Paper:Papers for Sections
Location: 555B/Convention Center
Date: Wednesday, August 4th, 2010
Time: 10:30 AM