Characterization of a L-Gulono-1,4-Lactone Oxidase Like Protein in the Floral Nectar of Mucuna sempervirens, Fabaceae.

Floral nectar plays important roles in the interaction between animal-pollinated plants and pollinators. Growing empirical evidence shows that most of the proteins secreted in nectar (nectarins) are enzymes that can tailor nectar chemistry for their animal mutualists or reduce the growth of microorganisms in nectar. However, to date, the function of many nectarins remains unknown, and very few plant species have had their nectar proteome thoroughly investigated. Mucuna sempervirens (Fabaceae) is a perennial woody vine native to China. Nectarins from this species were separated using two-dimensional gel electrophoresis, and analyzed using mass spectrometry. A L-gulonolactone oxidase like protein (MsGulLO) was detected. MsGulLO has high similarity to L-gulonolactone oxidase 5 (AtGulLO5) in Arabidopsis thaliana, which was suggested to be involved in the pathway of ascorbate biosynthesis; however both MsGulLO and AtGulLO5 are divergent from animal L-gulonolactone oxidases. MsGulLO is suggested to function in hydrogen peroxide generation in nectar but not in plant ascorbate biosynthesis.