Investigations of self-incompatibility in distylous and homostylous Turnera and Piriqueta (Turneraceae): Pollen tube and immunoblot analyses

I investigate self-incompatibility in distylous and homostylous Turnera and Piriqueta using pollen tube growth and inhibition data, and using molecular investigations of putative self-incompatibility proteins. Using the same techniques, I test the predictions of the recombinant hypothesis for the origin of homostyly.

I show the presence of a strong self-incompatibility system in six distylous species in the Turneraceae, using aniline blue staining of pollen tubes and fluorescence microscopy. I also show differential pollen tube inhibition between the morphs. Quantitatively, long-self pollen tubes generally grow further into the style than short-self pollen tubes. Qualitatively, long-self pollen tubes possess callose plugs, whereas, short-self pollen tubes do not. This is the first study to report a difference between the shorts and longs in callose plug presence or absence. At the molecular level, there is differential protein expression in short versus long styles from six distylous species. A short-specific style protein of ∼40kD was detected in short-styled, but not long-styled plants, using SDS-PAGE and immunoblotting. IEF gel electrophoresis and immunoblotting detected a short-specific pollen protein in some, but not all, individuals. Morphological and molecular differences between the morphs are discussed, and a potential difference between the morphs in the mechanism of self-incompatibility is suggested.

Finally, I test the predictions of the recombinant hypothesis for the evolution of homostyly by performing crosses between distylous and homostylous species in the Turneraceae. The recombinant hypothesis is supported for half of the crosses, while the results for the other do not fully support the hypothesis. Molecular investigations testing this hypothesis, using six homostylous species, support the hypothesis for the style protein, but not the pollen protein. This is the first study to test the recombinant hypothesis using molecular methods that explore the distribution of putative incompatibility proteins.