It's Not Easy Being Blue: Are There Olfactory and Visual Trade-Offs in Plant Signalling?

Understanding the signals used by plants to attract seed disperses is a pervasive quest in evolutionary and sensory biology. Fruit size, colour, and odour variation have long been discussed in the controversial context of dispersal syndromes targeting olfactory-oriented versus visually-oriented foragers. Trade-offs in signal investment could impose important physiological constraints on plants, yet have been largely ignored. Here, we measure the reflectance and volatile organic compounds of a community of Malagasy plants and our results indicate that extant plant signals may represent a trade-off between olfactory and chromatic signals. Blue pigments are the most visually-effective--blue is a colour that is visually salient to all known seed dispersing animals within the study system. Additionally, plants with blue-reflecting fruits are less odiferous than plants that reflect primarily in other regions of the colour spectrum.

Colour and odour drive fruit selection and seed dispersal by mouse lemurs.

Animals and fruiting plants are involved in a complex set of interactions, with animals relying on fruiting trees as food resources, and fruiting trees relying on animals for seed dispersal. This interdependence shapes fruit signals such as colour and odour, to increase fruit detectability, and animal sensory systems, such as colour vision and olfaction to facilitate food identification and selection. Despite the ecological and evolutionary importance of plant-animal interactions for shaping animal sensory adaptations and plant characteristics, the details of the relationship are poorly understood. Here we examine the role of fruit chromaticity, luminance and odour on seed dispersal by mouse lemurs. We show that both fruit colour and odour significantly predict fruit consumption and seed dispersal by Microcebus ravelobensis and M. murinus. Our study is the first to quantify and examine the role of bimodal fruit signals on seed dispersal in light of the sensory abilities of the disperser.

Atmospheric oxidation of polyfluorinated amides: historical source of perfluorinated carboxylic acids to the environment.

Polyfluorinated amides (PFAMs) are a class of fluorinated compounds which were produced as unintentional byproducts in the electrochemical fluorination process used for polyfluorinated sulfonamide synthesis in 1947-2002. To investigate the historical potential of PFAMs as an atmospheric perfluorinated acid (PFCA) source we studied N-ethylperfluorobutyramide (EtFBA) as a surrogate for longer chained PFAMs. Smog chamber relative rate techniques were used to measure bimolecular rate coefficients for reactions of EtFBA with chlorine atoms and hydroxyl radicals. It was found kCl = (2.08 ± 0.15) × 10(-11) cm(3) molecule(-1) s(-1) and kOH = (2.65 ± 0.50) × 10(-12) cm(3) molecule(-1) s(-1) and the atmospheric lifetime of EtFBA with respect to reaction with OH was estimated to be approximately 4.4 days. Offline sampling with both GC-MS and LC-MS/MS techniques was used to determine the products and hence a plausible pathway of atmospheric oxidation of EtFBA. Three primary oxidation products were observed by GC-MS, the N-dealkylation product C3F7C(O)NH2 and two carbonyl products, probably C3F7C(O)N(H)C(O)CH3 and C3F7C(O)N(H)CH2CHO. These primary products react further to give perfluorocarboxylic acids (PFCAs) as detected by LC-MS/MS, suggesting that eight carbon PFAMs were a historical source of PFCAs to remote regions, including the Canadian Arctic.

Polyfluorinated amides as a historical PFCA source by electrochemical fluorination of alkyl sulfonyl fluorides.

Polyfluorinated amides (PFAMs) are a class of compounds produced as byproducts of polyfluorinated sulfonamide synthesis by electrochemical fluorination (ECF). We measured four PFAM derivatives of perfluorooctanoic acid (PFOA) in a wide range of compounds, experimental materials, and commercial products synthesized by ECF. Initial screening was performed using headspace solid phase microextraction gas chromatography mass spectrometry (SPME-GC-MS), and quantification using in-house synthesized standards was accomplished with GC-MS using positive chemical ionization. Two monosubstituted PFAMs, N-methylperfluorooctanamide (MeFOA) and N-ethylperfluorooctanamide (EtFOA), were detected in the majority of materials that were analyzed. Two disubstituted PFAMs, N-methyl-N-(2-hydroxyethyl)perfluorooctanamide (MeFOAE) and N-ethyl-N-(2-hydroxyethyl)perfluorooctanamide (EtFOAE), were not detected in any sample, likely because they were never synthesized. The concentrations of PFAMs in the sulfonamide compounds under study ranged from 12 to 6736 µg/g, suggesting their historical importance as PFCA precursors. In each case, branched isomers for PFAMs were detected, providing further support for their link to an ECF source. A hydrolysis study performed at pH 8.5 showed no degradation of EtFOA to PFOA after 8 days due to the stability of the amide bond. The environmental fate of PFAMs is suggested to be volatilization to the atmosphere followed by oxidation by hydroxyl radical with a predicted lifetime of 3-20 days. Subsequent PFAM exposure to biota will likely lead to enzymatic hydrolysis of the amide linkage to give a PFCA. Human exposure to PFAMs may have contributed to the presence of branched PFOA isomers in blood by serving as an indirect source. The decline in PFOA concentrations in human blood is consistent with a significant drop in PFAM production concurrent with the POSF phase-out in 2000-2001.

Enzymatic kinetic parameters for polyfluorinated alkyl phosphate hydrolysis by alkaline phosphatase.

The hydrolysis kinetics of three polyfluorinated alkyl phosphate monoesters (monoPAPs), differing in fluorinated chain length, were measured using bovine intestinal alkaline phosphatase to catalyze the reaction. Kinetic values were also measured for analogous hydrogenated phosphate monoesters to elucidate the effects of the fluorinated chain on the rate of enzymatic hydrolysis. Michaelis constants (K(m)) were obtained by a competition kinetics technique in the presence of p-nitrophenyl phosphate (PNPP) using UV-vis spectroscopy. Compared with K(m) (PNPP), Michaelis constants for monoPAPs ranged from 0.9 to 2.1 compared with hydrogenated phosphates, which ranged from 4.0 to 13.0. Apparent bimolecular rate constants (k(cat)/K(m)) were determined by monitoring rates of product alcohol formation at low substrate concentrations using gas chromatography-mass spectrometry. The experimental values for k(cat)/K(m) averaged as 1.1 × 10(7) M(-1) s(-1) for monoPAPs compared with 3.8 × 10(5) M(-1) s(-1) for hexyl phosphate. This suggests that the electron-withdrawing nature of the fluorinated chain enhanced the alcohol leaving group ability. The results were used in a simple model to suggest that monoPAPs in a typical mammalian digestive tract would hydrolyze in approximately 100 s, supporting a previous study that showed its absence after a dosing study in rats.

Atmospheric degradation of perfluoro-2-methyl-3-pentanone: photolysis, hydrolysis and hydration.

Perfluorinated carboxylic acids are widely distributed in the environment, including remote regions, but their sources are not well understood. Perfluoropropionic acid (PFPrA, CF(3)CF(2)C(O)OH) has been observed in rainwater but the observed amounts can not be explained by currently known degradation pathways. Smog chamber studies were performed to assess the potential of photolysis of perfluoro-2-methyl-3-pentanone (PFMP, CF(3)CF(2)C(O)CF(CF(3))(2)), a commonly used fire-fighting fluid, to contribute to the observed PFPrA loadings. The photolysis of PFMP gives CF(3)CF(2)C·(O) and ·CF(CF(3))(2) radicals. A small (0.6%) but discernible yield of PFPrA was observed in smog chamber experiments by liquid chromatography-mass spectrometry offline chamber samples. The Tropospheric Ultraviolet-Visible (TUV) model was used to estimate an atmospheric lifetime of PFMP with respect to photolysis of 4-14 days depending on latitude and time of year. PFMP can undergo hydrolysis to produce PFPrA and CF(3)CFHCF(3) (HFC-227ea) in a manner analogous to the Haloform reaction. The rate of hydrolysis was measured using (19)F NMR at two different pHs and was too slow to be of importance in the atmosphere. Hydration of PFMP to give a geminal diol was investigated computationally using density functional theory. It was determined that hydration is not an important environmental fate of PFMP. The atmospheric fate of PFMP seems to be direct photolysis which, under low NO(x) conditions, gives PFPrA in a small yield. PFMP degradation contributes to, but does not appear to be the major source of, PFPrA observed in rainwater.

Environmental properties of pentafluorosulfanyl compounds: physical properties and photodegradation.

The pentafluorosulfanyl (SF5) functional group was investigated from an environmental perspective to ascertain its physical properties and photolytic fate. Five aromatic probe compounds were compared with their trifluoromethyl analogs. Water solubilities for SF5 compounds ranged from 78 mg/L to 2.4 g/L. Octanol-water partitioning coefficients ranged from log K(OW) = 2.9 to 3.6, all of which were approximately 0.5 to 0.6 log units more hydrophobic than their trifluoromethyl analogs. The direct photolytic fate of SF5 compounds was studied, and the SF5 group was found to completely degrade using actinic radiation with hourly half-lives. The reaction was followed by high-performance liquid chromatography with a UV-visible detector, 19F nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. It was found that five equivalents of fluoride were released to form a benzenesulfonate as a final product of photodegradation. Finally, an SF5 analog of fluometuron, a potentially new herbicide, was synthesized and likewise photolyzed. The present study provides the first evidence that pentafluorosulfanyl can degrade under mild, environmentally relevant conditions.