Proteins in gymnosperm pollination drops.
Date
2014-12-18
Authors
Prior, Natalie Annastasia
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Abstract
Most gymnosperms produce a pollination drop that captures and transports pollen into the ovule. Pollination drops have other functions. These include influencing pollen germination and pollen tube growth, defending the ovule from pathogens and providing a food reward in insect-pollinated gymnosperms. Mineral and organic molecules, including proteins, are responsible for these additional functions. To date, pollination drops from a handful of conifers and one non-conifer gymnosperm, Welwitschia mirabilis, have been subjected to proteomic analysis. In the present study, tandem mass spectrometry was used to detect proteins in all gymnosperm lineages: cycads (Ceratozamia hildae, Cycas rumphii, Zamia furfuracea); Gnetales (Ephedra compacta, E. distachya, E. foeminea, E. likiangensis, E. minuta, E. monosperma, E. trifurca; Gnetum gnemon; Welwitschia mirabilis); Ginkgo biloba; conifers (Taxus x media). PEAKS 6 DB (Bioinformatics Solutions, Waterloo, ON, Canada) was used to make protein identifications. Proteins were detected in all gymnosperm species analyzed. The numbers of proteins identified varied between samples as follows: one protein in Welwitschia female; nine proteins in Cycas rumphii; 13 proteins on average in Ephedra spp.; 17 proteins in Gnetum gnemon; 38 proteins on average in Zamia furfuracea; 57 proteins in Ginkgo biloba; 61 proteins in Ceratozamia hildae; 63 in Taxus x media; 138 proteins in Welwitschia male. The types of proteins identified varied widely. Proteins involved in carbohydrate modification, e.g. galactosidase, chitinase, glycosyl hydrolase, glucosidase, were present in most gymnosperms. Similarly, defence proteins, e.g. reduction-oxidation proteins, lipid-transfer proteins and thaumatin-like proteins, were identified in many gymnosperms. Gymnosperms that develop a deep pollen chamber as the nucellus degrades, e.g., cycads, Ginkgo, Ephedra, generally contained higher proportions of proteins localized to intracellular spaces. These proteins represent the pollination drop degradome. Gymnosperms that either lack a pollen chamber, e.g. Taxus, or have a shallow pollen chamber, e.g. Gnetum, had greater proportions of extracellular proteins. These proteins represent the pollination drop secretome. Our proteomic analyses support the hypothesis that the pollination drops of all extant gymnosperms constitute complex reproductive secretions.
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Keywords
gymnosperm, pollination drop, cycad, gnetales, Ginkgo, Cycas, Zamia, Ceratozamia, Gnetum, Ephedra, Welwitschia, Taxus x media, plant reproductive secretion, plant proteome