Bilirubin Present in Diverse Angiosperms

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 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 color. Previously, no tetrapyrroles were known to generate display color in plants. We were therefore interested in determining whether bilirubin is broadly distributed in the plant kingdom, and whether it contributes to color in other species.

Anthocyanins in Leaves: Distribution, Phylogeny and Development

Red pigments, products of different metabolic pathways, occur in terrestrial plants. The flavonoid pathway contributes the greatest diversity, culminating in the prevalence of anthocyanins in the angiosperms. Anthocyanins are produced in flowers and fruits, and also in vegetative organs, but have been poorly researched in the latter. Anthocyanins are commonly produced in: 1. rapidly expanding leaves of tropical plants; 2. senescing leaves of temperate plants; 3. undersurfaces of floating leaves of aquatic plants; 4. abaxial surfaces of leaves of understory plants; and 5. leaves subjected to various environmental stresses. The distribution of anthocyanins in leaves, both in presence and in tissue distribution, is influenced by both phylogeny and development. Few species produce anthocyanins in leaf tissues derived from both dermal and ground embryonic tissue. These influences will be important in resolving the ecological roles of anthocyanins in leaves.