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Characterization of A. thaliana Pollen Tube-Ovule
interactions
As tubes left the style, they dispersed (Fig. 1e and see 1), growing at 2.5 ± 1.0 (s.d)
µ m/min (n = 20) and up to 3 mm before reaching an ovule (Fig. 2a-f ). Near a vir-
gin ovule, however, growth rates decreased (1.2 ± 0.59 (s.d) µ m/min (n = 20; Fig.
2a-f ) and the tubes often made sharp turns (Fig. 1d, arrows) within 33 ± 20 (s.d)
mm of a micropyle (avg. 60 ± 38° (s.d); n = 60). Pollen tube guidance to ovules was
abolished when fertilized or heat-treated ovules were used (Table 1), indicating they
release a diffusible, heat-labile attractant prior to fertilization. Tube entry into the
ovule appears to be not influenced by the number of tubes near a micropyle; target-
ing was achieved regardless of whether one or multiple tubes were in the vicinity
of an ovule. When approaching an ovule, the in vitro grown pollen tubes did not
always migrate up a funiculus, Fig. 1c) before entering it. To directly test the role
of this tissue, we removed funiculi from ovules, revealing a small but significant
decrease in targeting efficiency (Table 1). These results indicate that an interaction
between the pollen tube and funiculus is not essential, yet this interaction enhances
successful entry into the ovule, perhaps by i) providing a physical support for pol-
len tubes to reach the micropyle, ii) aiding in the generation and maintenance of a
signal gradient, or iii) enhancing the availability of ovule-derived guidance signals.
Figure 2. Pollen tube navigation time course.
(a-f ) Graphs of position ( µ m; X axis) versus growth rate ( µ m/min; Y axis) for six pollen tubes, from the moment
they exit the style (white bar), enter the micropyle (arrow) and navigate within the ovule (black bar). (g-l)
Merged fluorescent and bright field images of a GFP-tagged pollen tube entering a micropyle (g), navigating
past diploid ovule cells (h-j), and pausing upon reaching a synergid (k), and completing lysis (l). Characterstics
of pollen tube growth within the ovule shown in G-L were graphed and shown in (e). Time is min ('); scale bar,
50 µ m.
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