Convergent evolution of a blood-red nectar pigment in vertebrate-pollinated flowers.

Nearly 90% of flowering plants depend on animals for reproduction. One of the main rewards plants offer to pollinators for visitation is nectar. Nesocodon mauritianus (Campanulaceae) produces a blood-red nectar that has been proposed to serve as a visual attractant for pollinator visitation. Here, we show that the nectar's red color is derived from a previously undescribed alkaloid termed nesocodin. The first nectar produced is acidic and pale yellow in color, but slowly becomes alkaline before taking on its characteristic red color. Three enzymes secreted into the nectar are either necessary or sufficient for pigment production, including a carbonic anhydrase that increases nectar pH, an aryl-alcohol oxidase that produces a pigment precursor, and a ferritin-like catalase that protects the pigment from degradation by hydrogen peroxide. Our findings demonstrate how these three enzymatic activities allow for the condensation of sinapaldehyde and proline to form a pigment with a stable imine bond. We subsequently verified that synthetic nesocodin is indeed attractive to Phelsuma geckos, the most likely pollinators of Nesocodon We also identify nesocodin in the red nectar of the distantly related and hummingbird-visited Jaltomata herrerae and provide molecular evidence for convergent evolution of this trait. This work cumulatively identifies a convergently evolved trait in two vertebrate-pollinated species, suggesting that the red pigment is selectively favored and that only a limited number of compounds are likely to underlie this type of adaptation.

Van Krevelen diagram visualization of high resolution-mass spectrometry metabolomics data with OpenVanKrevelen.

INTRODUCTION: Van Krevelen (VK) diagrams provide a promising but uncommon solution to a number of challenges associated with the visualization of metabolomics data. VK diagrams are created by plotting H:C ratios against O:C ratios of the compounds in a chemical mixture. OBJECTIVES: The aim of this manuscript is to present an open-source software tool and reference map that we have developed to make VK diagrams for visualization of metabolomics data. METHODS: Software was created with a prompt-driven command line user interface and was written using Python 2.7. We empirically derived an accompanying map by plotting where compounds from seven biomolecule types fall within the VK plot space. RESULTS: We've created an easy to use, open source software tool named OpenVanKrevelen for making a range of VK diagrams that is available on GitHub: https://github.com/HegemanLab/VanKrevelenLocal . The empirical mapping approach has produced several improvements from previously published maps. CONCLUSIONS: OpenVanKrevelen provides the metabolomics community with access to a new tool for visualization of complex metabolomics datasets.

Multispectral phloem-mobile probes: properties and applications.

Using Arabidopsis (Arabidopsis thaliana) seedlings, we identified a range of small fluorescent probes that entered the translocation stream and were unloaded at the root tip. These probes had absorbance/emission maxima ranging from 367/454 to 546/576 nm and represent a versatile toolbox for studying phloem transport. Of the probes that we tested, naturally occurring fluorescent coumarin glucosides (esculin and fraxin) were phloem loaded and transported in oocytes by the sucrose transporter, AtSUC2. Arabidopsis plants in which AtSUC2 was replaced with barley (Hordeum vulgare) sucrose transporter (HvSUT1), which does not transport esculin in oocytes, failed to load esculin into the phloem. In wild-type plants, the fluorescence of esculin decayed to background levels about 2 h after phloem unloading, making it a suitable tracer for pulse-labeling studies of phloem transport. We identified additional probes, such as carboxytetraethylrhodamine, a red fluorescent probe that, unlike esculin, was stable for several hours after phloem unloading and could be used to study phloem transport in Arabidopsis lines expressing green fluorescent protein.