We describe for distylous Turnera subulata a polygalacturonase specific to short-styled plants that is localized to the style transmitting tissue (the tissue through which pollen tubes grow). The polygalacturonase gene is linked to and may be upregulated by the S allele of the distyly locus. Because of its tissue-specific location, the polygalacturonase may be involved in the self-incompatibility response, acting in a complementary or antagonistic manner, or possibly in signalling downstream events. A pollen-specific polygalacturonase was also identified and may be a member of a small multigene family of pollen polygalacturonases. The role, if any, played by the pollen polygalacturonase in distyly, is presently unknown.

Abstract:We investigate sites of incompatibility for five Turnera L. species and for Piriqueta caroliniana (Walt.) Urban using aniline blue staining of pollen tubes and fluorescence microscopy. We show that sites of incompatibility occur in the stigma and upper regions of the style. There is an asymmetry between the morphs where, following selfing, pollen tubes tend to grow further into long-styled compared to short-styled plants, although the difference is not particularly marked. We demonstrate for the first time a qualitative difference in the appearance of pollen tubes. Upon self-pollination, pollen tubes in short-styled plants do not produce callose plugs, while all other pollinations result in callose plug formation. This could indicate that there is a difference in the mechanisms of incompatibility between the morphs. Exploiting crosses between two populations of Turnera scabra Millsp. that differ in flower size, we found no support for the hypothesis that incompatibility of long-styled plants is the result of insufficient nutrient reserves in pollen. Bud-pollinations provided limited support for the hypothesis that a short-specific style protein is involved in incompatibility. Crosses between distylous and homostylous species provided support for a recombinant origin for homostyly for four species, while deviations from this expectation were observed in four instances.Key words: distyly, homostyly, self-incompatibility, callose, pollen tubes, Turnera.Résumé : Les auteurs ont étudié les sites d'incompatibilité chez cinq espèces de Turnera L. et chez le Piriqueta caroliniana (Walt.) Urban, en utilisant la microscopie en fluorescense après avoir coloré les tubes polliniques au bleu d'aniline. On montre qu'il y a des sites d'incompatibilité dans les stigmates et dans les régions supérieures du style. Il y a asymétrie entre les morphes où, suite à l'autofécondation, les tubes polliniques ont tendance à pousser plus loin dans les styles longs que dans les styles courts, bien que la différence ne soit pas très marquée. On démontre pour la première fois une différence qualitative dans l'apparence des tubes polliniques. Suite à l'auto-pollinisation, chez les plantes à styles courts, les tubes polliniques ne produisent pas de bouchon de callose, alors que dans toutes les autres pollinisations il y formation de bouchons de callose. Ceci suggère une différence dans les mécanismes d'incompatibilité entre les morphes. En exploitant les croisements entre deux populations du Turnera scabra Millsp., qui diffèrent selon la dimension de leurs fleurs, les auteurs n'ont trouvé aucune preuve supportant l'hypothèse que l'incompatibilité chez les plantes à styles longs résulterait de réserves nutritives insuffisantes dans le pollen. Les pollinisations des bourgeons n'offrent qu'un support limité à l'idée qu'une protéine spécifique aux fleurs à style court, serait impliquée dans l'incompatibilité. Les croisements entre les espèces distyles et homostyles supportent l'idée de l'origine recombinatoire pour l'homostylie chez quatre ...

We used nondenaturing isoelectric focusing (IEF) in a survey of plants from 11 populations to identify style and pollen proteins unique to the short-styled morph of Turnera scabra, T. subulata and T. krapovickasii. Three protein bands [approximately isoelectric points (pIs) 6.1, 6.3 and 6.5] were found only in styles and stigmas of short-styled plants while two bands (approximately pIs 6.7 and 6.8, M  r 56 and 59 kD) occur only in pollen of short-styled plants. Some of these bands appear very late in development, within 24 hr before flowering. Two isozyme loci were mapped to an 8.7 cM region spanning the distyly locus. Using these isozyme markers we identified progeny exhibiting recombination adjacent to the distyly locus. No recombinants between the distyly locus and the locus or loci controlling the presence of the short-styled morph-specific proteins were obtained. This suggests that the loci encoding these proteins are either extremely tightly linked to the distyly locus and in complete disequilibrium with the S allele or exhibit morph-limited expression. Crosses to a plant showing an unusual style protein phenotype demonstrated that an additional unlinked locus is required for full expression of the style proteins. The function of the morph-specific proteins is unknown