Observations of pollen tube growth in Nicotiana alata and their implications for the mechanism of self-incompatibility |
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Authors: | W M Lush Adrienne E Clarke |
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Institution: | (1) Plant Cell Biology Research Centre, School of Botany, University of Melbourne, Parkville, Victoria 3052, Australia Fax +61–3–9347 1071; e-mail w.lush@botany.unimelb.edu.au, AU |
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Abstract: | Style squashes and stylar grafts were used to examine the growth of Nicotiana alata pollen tubes in self-compatible and self-incompatible styles. Compatible tubes typically showed a uniform layer of callose
deposition in the walls and in small plugs spaced at regular intervals within the tube. Incompatible tubes were characterised
by the variability of callose deposition in the walls and by larger, closer and more irregularly spaced plugs. There was no
difference in the growth rate of compatible and incompatible tubes during growth through the stigma, but within the style
most compatible tubes grew 20–25 mm day-1 (maximum 30 mm day–1), whereas incompatible tubes grew 1.0–1.5 mm day-1 (maximum 5 mm day–1). Many incompatible tubes continued to grow until flowers senesced, and only a small proportion died as a consequence of
tip bursting. Grafting compatibly pollinated styles onto incompatible styles showed that the incompatible reaction could occur
in pollen tubes between 2 and 50 mm long, and that inhibition of pollen tube growth occurred in both the upper and lower parts
of the transmitting tract. Grafting incompatibly pollinated styles onto compatible styles showed that the incompatible reaction
was fully reversible in at least a proportion of the pollen tubes. The findings are not consistent with the cytotoxic model
of inhibition of self-pollen tubes in solanaceous plants, which assumes that the incompatible response results from the degradation
of a finite amount of rRNA present in the pollen tube. However, if pollen tubes do in fact synthesise rRNA, the findings become
consistent with this model.
Received: 23 May 1996 / Revision accepted: 22 August 1996 |
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Keywords: | Nicotiana alata Pollen tube growth Stylar graft Self-incompatibility Cytotoxic model |
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