Strelitzia reginae (family Strelitziaceae, order: Zingiberales), the Bird of Paradise plant, is an herbaceous monocot native to South Africa but widely cultivated in warm temperate and tropical regions. Aside from the shape of its inflorescence, which resembles the head of a bird, S. reginae is also admired for its brilliant floral coloration. Each flower is composed of three vibrant orange sepals and three blue petals (Fig. 1A). At least 19 carotenoids are present in the sepals (Simpson et al., 1975; Tappi and Menziani, 1955), and the anthocyanin delphinidin- 3-rutinoside is found in the petals (Harbourne, 1967). Anthocyanins are stored in the vacuole of petal cells (Kronsteadt and Walles, 1986), whereas carotenoids in mature sepal tissue are stored in spindle-shaped chromoplasts (Simpson et al., 1975). Petal color is enhanced by papillar processes in the epidermis, which refract light (Kronsteadt and Walles, 1986).
In contrast to the conspicuous flowers, the capsular fruit of S. reginae is pale and partially obscured by the bract during development. However, at maturity, the capsule breaks open to reveal intensely colored orange arillate seeds (Fig. 1B–C). Remarkably, aril color remains unchanged years after cell death, a quality that likely contributes to the continued attraction of avian frugivores (Frost, 1980). We recently found the orange tetrapyrrole bilirubin to be the primary pigment in the arils of Strelitzia nicolai, a close relative of S. reginae (Pirone et al., 2009). Bilirubin was previously known in the animal kingdom where it is produced as a breakdown product of heme. Preliminary high-performance liquid chromatography (HPLC) and ultraviolet-visible (ultraviolet) spectrometry analyses suggested that bilirubin is also present in the arils of S. reginae. We were therefore interested in whether this unusual pigment is indeed present in those arils and whether it is also present in the flowers. We used HPLC/ultraviolet and HPLC/ultraviolet/electrospray ionization–tandem mass spectrometry (HPLC/ultraviolet/ESI-MS/MS) to investigate these questions. We also observed the aril cells using light microscopy to determine the location of pigment within the aril and sepal cells.
Pirone, C.L. , Quirke, J.M.E. , Priestap, H. & Lee, D.W. 2009 Animal pigment bilirubin discovered in plants J. Amer. Chem. Soc. 131 2830
Simpson, D.J. , Baqar, M.R. & Lee, T.H. 1975 Ultrastructure and carotenoid composition of chromoplasts of the sepals of Strelitzia reginae Aiton during floral development Ann. Bot. (Lond.) 39 175 183
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