Bilirubin present in diverse angiosperms

AoB PLANTS http://aobplants.oxfordjournals.org/ Open access – Research article Bilirubin present in diverse angiosperms Cary Pirone 1*, Jodie V. Johnson 2, J. Martin E. Quirke 3, Horacio A. Priestap1 and David Lee 1 1 Department of Biological Sciences, Florida International University, 11200 SW 8 St., OE-167, Miami, FL 33199, USA Department of Chemistry, University of Florida, PO Box 117200, Gainesville, FL 3261, USA 3 Department of Chemistry and Biochemistry, Florida International University, 11200 SW 8 St., CP-304, Miami, FL 33199, USA 2 Received: 20 August 2010; Returned for revision: 25 September 2010; Accepted: 24 October 2010; Published: 28 October 2010 Citation details: Pirone C, Johnson JV, Quirke JME, Priestap HA, Lee D. 2010. Bilirubin present in diverse angiosperms. AoB PLANTS 2010: plq020, doi:10.1093/aobpla/plq020 Abstract Background and aims Bilirubin is an orange-yellow tetrapyrrole produced from the breakdown of heme by mammals and some other vertebrates. Plants, algae and cyanobacteria synthesize molecules similar to bilirubin, including the protein-bound bilins and phytochromobilin which harvest or sense light. Recently, we discovered bilirubin in the arils of Strelitzia nicolai, the White Bird of Paradise Tree, which was the first example of this molecule in a higher plant. Subsequently, we identified bilirubin in both the arils and the flowers of Strelitzia reginae, the Bird of Paradise Flower. In the arils of both species, bilirubin is present as the primary pigment, and thus functions to produce colour. Previously, no tetrapyrroles were known to generate display colour in plants. We were therefore interested in determining whether bilirubin is broadly distributed in the plant kingdom and whether it contributes to colour in other species. Methodology In this paper, we use HPLC/UV and HPLC/UV/electrospray ionization-tandem mass spectrometry (HPLC/UV/ESI-MS/MS) to search for bilirubin in 10 species across diverse angiosperm lineages. Principal results Bilirubin was present in eight species from the orders Zingiberales, Arecales and Myrtales, but only contributed to colour in species within the Strelitziaceae. Conclusions The wide distribution of bilirubin in angiosperms indicates the need to re-assess some metabolic details of an important and universal biosynthetic pathway in plants, and further explore its evolutionary history and function. Although colour production was limited to the Strelitziaceae in this study, further sampling may indicate otherwise. Introduction Tetrapyrroles occur throughout the plant kingdom; this class of molecules includes vital biosynthetic products such as chlorophyll and heme. In plants, the degradation of heme forms first biliverdin-IXa, and subsequently phytochromobilin, the precursor of the phytochrome chromophore, an essential light-sensing molecule (Tanaka and Tanaka 2007). In mammals and some vertebrates, biliverdin-IXa is also formed from the degradation of heme, but it is transformed into the yellow-orange pigment bilirubin-IXa. We have identified bilirubin-IXa (henceforth referred to as bilirubin) as the major pigment in the orange arils of Strelitzia nicolai, the White Bird of Paradise Tree (Pirone et al. 2009). Although ubiquitous in animals, this is the first example of bilirubin in a plant. Subsequently, we have discovered this pigment * Corresponding author’s e-mail address: AoB PLANTS Vol. 2010, plq020, doi:10.1093/aobpla/plq020, available online at www.aobplants.oxfordjournals.org & The Authors 2010. Published by Oxford University Press. This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/2.5/uk/) which permits unrestricted noncommercial use, distribution, and reproduction in any medium, provided the original work is properly cited. AoB PLANTS Vol. 2010, plq020, doi:10.1093/aobpla/plq020 & The Authors 2010 1 2 — — — — — — — ,44 ng g21 Y N N N N N Fruit Fruit Lauraceae Myrtaceae P. americana E. luschnathiana Laurales Pandanaceae P. odoratissimus Myrtales — — N N N Fruit ,44 ng g Y N N Fruit Arecaceae G. crispa Arecales Zingiberaceae H. coronarum Pandanales — ,44 ng g 21 ,44 ng g 3.725 mg g21 Strelitziaceae P. guyanense Zingiberales Aril N N Y ,44 ng g 21 21 5.787 mg g21 21 3.041 mg g21 Y Y N/A Aril Strelitziaceae R. madagascariensis Zingiberales 0.001 mg g21 0.001 mg g 0.001 mg g Y Y N/A Aril Costaceae Zingiberales ,44 ng g Y N N Flower 21 — ,44 ng g — C. lucanusianus Zingiberales 21 21 21 ,44 ng g21 — Y N N Fruit Zingiberales Heliconiaceae concentration Mean BR BR concentration ..................................... Sample 1 Sample 2 HPLC-MS/MS HPLC/UV diazomethane BR detection via BR detection via BR detection via Organ Order Family AoB PLANTS Vol. 2010, plq020, doi:10.1093/aobpla/plq020 & The Authors 2010 H. collinsiana Plant material was collected from Fairchild Tropical Botanic Garden in Miami, FL, except aril tissue from S. reginae, which was obtained from Ellison Horticulture derivative (n 5 2) ........................................................................................................................................................................................................................... 21 21 M. balbisiana Musaceae Zingiberales Peel N N Y ,44 ng g ,44 ng g — Materials and methods Species in the sepals and arils of Strelitzia reginae, the Bird of Paradise Flower, indicating that the pigment is not unique to S. nicolai (Pirone et al. 2010). In S. nicolai and S. reginae, bilirubin is a novel biosynthetic source of display colour. As a rule, the colouration of flowers and fruits is achieved with products from three metabolic pathways: the terpenoid (carotenoids), the phenylpropanoid (flavonoids) and the betalain (betalains) (Davies 2004; Grotewold 2006; Lee 2007). Betalain synthesis is restricted to families in the order Caryophyllales, while carotenoids and flavonoids (including anthocyanins) are pervasive in the plant kingdom (Harborne 1967; Goodwin 1988). A rare group of pigments, the phenalenones, has been documented in several species in the Strelitziaceae and related families (Davies 2004). However, to our knowledge, neither the phenalenones nor the other rare pigments play a significant role in colour production. Bilirubin is thus the first product of an additional biosynthetic route, the tetrapyrrole pathway, to produce conspicuous colour in a plant reproductive structure. Chlorophylls, which are also synthesized via the tetrapyrrole pathway, primarily produce colour in foliage, thus forming a green background upon which the contrasting colours of flowers and fruits are displayed. While chlorophylls occasionally produce colour in reproductive structures, these are fairly inconspicuous. Given the presence of bilirubin in Strelitzia, it is interesting to determine whether the (...truncated)