Bilirubin: an Animal Pigment in the Zingiberales and Diverse Angiosperm Orders

• Main Author: Pirone, Cary L
• Format: Others
• Published: FIU Digital Commons 2010
• Subjects: Zingiberales; bilirubin; Strelitzia; pigment; aril; Biochemistry; Botany; Plant Sciences
• Online Access: http://digitalcommons.fiu.edu/etd/336; http://digitalcommons.fiu.edu/cgi/viewcontent.cgi?article=1393&context=etd

Strelitziaceae is a tropical monocot family comprising three genera and seven species: Ravenala Adans and Phenkospermum Endl., which are monotypic, and five species of Strelitzia Aiton. All species produce woody capsular fruits that contain vibrantly colored arillate seeds. Arils of the Strelitzia species are orange, those of Phenakospermum are red, and those of Ravenala are blue. Unlike most plant pigments, which degrade after cell death, aril pigments in the family persist for decades. Chemical properties of the compounds are unusual, and do not match those of known pigment classes (carotenoids, flavonoids, betalains, and the chlorophylls). I isolated the orange pigment from the arils of Strelitzia nicolai, and performed HPLC-ESMS, UV-visible, 1H NMR and 13C NMR analyses to determine its chemical structure. These data indicated the pigment was bilirubin-IX, an orange-yellow tetrapyrrole previously known only in mammals and some other vertebrates as the breakdown product of heme. Although related tetrapyrroles are ubiquitous throughout the plant kingdom and include vital biosynthetic products such as chlorophyll and phytochromobilin, this is the first report of bilirubin in a plant, and evidence of an additional biosynthetic pathway producing orange coloration in flowers and fruits.