Sexual dimorphism of staminate- and pistillate-phase flowers of Saponaria officinalis (bouncing bet) affects pollinator behavior and seed set.

The sequential separation of male and female function in flowers of dichogamous species allows for the evolution of differing morphologies that maximize fitness through seed siring and seed set. We examined staminate- and pistillate-phase flowers of protandrous Saponaria officinalis for dimorphism in floral traits and their effects on pollinator attraction and seed set. Pistillate-phase flowers have larger petals, greater mass, and are pinker in color, but due to a shape change, pistillate-phase flowers have smaller corolla diameters than staminate-phase flowers. There was no difference in nectar volume or sugar content one day after anthesis, and minimal evidence for UV nectar guide patterns in staminate- and pistillate-phase flowers. When presented with choice arrays, pollinators discriminated against pistillate-phase flowers based on their pink color. Finally, in an experimental garden, in 2012 there was a negative correlation between seed set of an open-pollinated, emasculated flower and pinkness (as measured by reflectance spectrometry) of a pistillate-phase flower on the same plant in plots covered with shade cloth. In 2013, clones of genotypes chosen from the 2012 plants that produced pinker flowers had lower seed set than those from genotypes with paler flowers. Lower seed set of pink genotypes was found in open-pollinated and hand-pollinated flowers, indicating the lower seed set might be due to other differences between pink and pale genotypes in addition to pollinator discrimination against pink flowers. In conclusion, staminate- and pistillate-phase flowers of S. officinalis are dimorphic in shape and color. Pollinators discriminate among flowers based on these differences, and individuals whose pistillate-phase flowers are most different in color from their staminate-phase flowers make fewer seeds. We suggest morphological studies of the two sex phases in dichogamous, hermaphroditic species can contribute to understanding the evolution of sexual dimorphism in plants without the confounding effects of genetic differences between separate male and female individuals.

Differential expression of saporin genes upon wounding, ABA treatment and leaf development.

Saporins are type 1 ribosome-inactivating proteins (RIPs: EC 3.2.2.22) produced in various organs of Saponaria officinalis L. Two distinct saporin types, saporin-L and saporin-S isoforms, were respectively purified from the intra- and extra-cellular fractions of soapwort leaves. The saporin-L isoform was lowly identical, differed for toxicity, molecular mass and amino acid composition from saporin-S proteins forming a new monophyletic group. Genes encoding both L- and S-type isoforms were cloned from leaf-specific cDNA library; the encoded products included the N-terminal diversity observed by protein sequencing and showed compatible weights with those from mass spectra. These genes were intron-less belonging to small gene families. Reverse transcription polymerase chain reaction/quantitative reverse transcription polymerase chain reaction experiments evidenced their differential expression during leaf development, wounding and abscisic acid treatment. These results suggest that the saporin-L and -S proteins may play diversified roles during stress responses.