Cell-to-Cell and Long Distance Signaling
Jackson, Jamie , Palanivelu, Ravishankar .
An Arabidopsis mutant defective in pollen tube repulsion.
After pollen lands on the surface of the pistil, it extends a long polar process that carries sperm to an ovule. Typically, only one pollen tube successfully enters the ovule micropyle and terminates its journey within a synergid cell by bursting to release sperm cells. Since ovules are penetrated by only one pollen tube, it has been hypothesized that additional tubes are actively repulsed by a targeted ovule. Previously, it has been shown that Arabdiopsis thaliana¬†in vitro¬†guidance assay recapitulates pollen tube repulsion near a targeted ovule. By performing real-time observations of pollen tube interactions with a targeted ovule, we first explored the divergence of repulsion mechanism that prevents multiple tubes from entering a targeted ovule. Characterization of pollen tube repulsion was carried out using repulsion data from two close species of A. thaliana; A. arenosa and Olimarabidopsis pumila. Results from these experiments demonstrated that even if targeted by A. thaliana pollen tubes, A. arenosa (25 instances, n=20 assays) and Olimarabidopsis pumila ovules (10 instances, n=20 assays) repel additional tubes that approach them. These results suggest that pollen tube repulsion is mediated by a signaling mechanism that does not evolve rapidly. Secondly, we used the in vitro guidance assay to characterize the pollen tube repulsion defects in a newly isolated mutant, ref1 (reduced fertility defect 1). Mutant ovules that have been already targeted by pollen tubes are markedly defective in repelling additional tubes that approach them (5 out of 12 instances, ~42%; n=20 assays) resulting in multiple tube entry into the micropyle. This percentage is significantly different from the behavior of wild type ovules in the in vitro assay; in every instance, wild type targeted ovules repelled additional tubes that approached them (0 out of 44. 0%; n=20 assays). Lack of repulsion in ref1 may point to decreased production of repellants upon ovule targeting.
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1 - University of Arizona, Plant Sciences
Presentation Type: Plant Biology Abstract
Location: Exhibit Hall (Northeast, Southwest & Southeast)/Hilton
Date: Sunday, July 8th, 2007
Time: 8:00 AM