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

Linking Self-Incompatibility, Dichogamy, and Flowering Synchrony in Two Euphorbia Species: Alternative Mechanisms for Avoiding Self-Fertilization?

Background: Plant species have several mechanisms to avoid selfing such as dichogamy or a self-incompatibility response. Dichogamy in a single flower may reduce autogamy but, to avoid geitonogamy, plants must show flowering synchronization among all their flowers (i.e. synchronous dichogamy). It is hypothesized that one species would not simultaneously show synchronous dichogamy and self-incompatibility because they are redundant mechanisms to reduce selfing; however, this has not been accurately assessed. Methodology/Principal Findings: This expectation was tested over two years in two natural populations of the closely related Mediterranean spurges Euphorbia boetica and E. nicaeensis, which completely avoid autogamy by protogyny at the cyathia level. Both spurges showed a high population synchrony (Z,79), and their inflorescences flower synchronously. In E. nicaeensis, there was no overlap among the cyathia in anthesis of successive inflorescence levels and the overlap between sexual phases of cyathia of the same inflorescence level was uncommon (4–16%). In contrast, E. boetica showed a high overlap among consecutive inflorescence levels (74–93%) and between sexual phases of cyathia of the same inflorescence level (48–80%). The flowering pattern of both spurges was consistent in the two populations and over the two successive years. A hand-pollination experiment demonstrated that E. nicaeensis was strictly self-compatible whereas E. boetica was partially self-incompatible. Conclusions/Significance: We propose that the complex pattern of synchronized protogyny in E. nicaeensis prevents geitonogamous crosses and, consequently, avoids selfing and inbreeding depression. In E. boetica, a high probability of geitonogamous crosses may occur but, alternatively, this plant escapes selfing through a self-incompatibility response. We posit that synchronous dichogamy and physiological self-incompatibility do not co-occur in the same species because each process is sufficiently effective in avoiding self-fertilization.España Ministerio de Ciencia y Tecnología PLO CGL2005-03731; CGL2008-02533-EEspaña Ministerio de Ciencia y Tecnología MA CGL2009-0825

Homology modeling of nitrogenase iron proteins from three Frankia strains

The NifH protein contains an iron-sulfur cluster performing different functions during nitrogen fixation. Frankia is an actinomycete, entering into symbiotic association with a number of dicotyledonous plants and fixing nitrogen. The structure of the Frankia NifH protein was determined using homology modelling technique. Metal binding sites and functionally important regions of the protein were analyzed. Thiol ligands and active sites help in protein functioning and conformations. Structurally important nests were recognized. Clefts and cavities contain biologically important residues. Site-directed mutagenesis results reveal that mutations in functional residues hamper nitrogen fixation. The structure is rigid with an accessible surface for solvents. The structure is reliable offering insights into the 3D structural framework as well as structure-function relation of NifH protein