Mechanistic insights from a quantitative analysis of pollen tube guidance
1 Department of Chemistry, The University of Chicago, 929 E 57th St, Chicago, IL 60637, USA
2 James Franck Institute, The University of Chicago, 929 E 57th St, Chicago, IL 60637, USA
3 Department of Molecular Genetics and Cell Biology, CLSC 1106, 920 E 58th St, Chicago, IL 60637, USA
4 Current address: Chromatin, Inc, 3440 S Dearborn St, Suite 280, Chicago, IL 60616, USA
5 Institute for Biophysical Dynamics, The University of Chicago, 929 E 57th Street, Chicago, IL 60637, USA
6 Department of Physics, The University of Chicago, 5740 S Ellis Ave, Chicago, IL 60637, USA
7 Department of Biology, Knox College, 2 E South St, Galesburg, IL 61401-4999, USA
8 International Institute of Information Technology, Gachibowli, Hyderabad 500 032, Andhra Pradesh, India
9 Current address: Department of Physiology and Biophysics, Albert Einstein College of Medicine of Yeshiva University, Jack and Pearl Resnick Campus, 1300 Morris Park Ave, Bronx, NY, 10461, USA
BMC Plant Biology 2010, 10:32 doi:10.1186/1471-2229-10-32Published: 22 February 2010
Plant biologists have long speculated about the mechanisms that guide pollen tubes to ovules. Although there is now evidence that ovules emit a diffusible attractant, little is known about how this attractant mediates interactions between the pollen tube and the ovules.
We employ a semi-in vitro assay, in which ovules dissected from Arabidopsis thaliana are arranged around a cut style on artificial medium, to elucidate how ovules release the attractant and how pollen tubes respond to it. Analysis of microscopy images of the semi-in vitro system shows that pollen tubes are more attracted to ovules that are incubated on the medium for longer times before pollen tubes emerge from the cut style. The responses of tubes are consistent with their sensing a gradient of an attractant at 100-150 μm, farther than previously reported. Our microscopy images also show that pollen tubes slow their growth near the micropyles of functional ovules with a spatial range that depends on ovule incubation time.
We propose a stochastic model that captures these dynamics. In the model, a pollen tube senses a difference in the fraction of receptors bound to an attractant and changes its direction of growth in response; the attractant is continuously released from ovules and spreads isotropically on the medium. The model suggests that the observed slowing greatly enhances the ability of pollen tubes to successfully target ovules. The relation of the results to guidance in vivo is discussed.