Submitted to: Encyclopedia on Health United Nations Education Scientific and Cultural Org
Publication Type: Book / Chapter
Publication Acceptance Date: 5/7/2000
Publication Date: N/A
Citation: Interpretive Summary: Plant carotenoids are red, orange, and yellow lipid-soluble pigments. Carotenoids play an essential role in the plant metabolism for photosynthesis and other relevant functions in plant biology such as harvesting sunlight, dissipating excess light energy, serving as precursors for biosynthesis of the hormone abscisic acid; and functioning as a color mechanism to guide pollinators to flowers as well as to attract agents of seed dispersal to fruits. The cleavage products of several dietary carotenoids, particularly B-carotene, fulfill essential requirements in human and animal nutrition (vitamin A), vision (retinal), and development (retinoic acid). Carotenoids also have additional benefits as food-coloring agents and apparently in prevention of some cancers. Vitamin A deficiency has been reported as the most common dietary problem affecting children worldwide. The top three natural sources of biologically active carotenes in the United States are vegetables (namely carrots, sweet potatoes, and tomatoes). Field crops are, in general poor natural sources of dietary provitamin A carotenoids. Carotenoid biosynthesis is a notable example of a well-characterized biochemical genetic pathway in plants. The modification in the copy number and/or the patterns of expression of these genes could give rise to novel and commercially attractive phenotypes. This review discusses the potential for using molecular approaches to increase vegetable carotenoid content. Its primary impact will be to develop an awareness of plant pigments by the general public.
Technical Abstract: Carotenoids are important for photosynthesis and color in plants and as the ultimate source of vitamin A for animals. The current knowledge of the molecular biology of carotenoids derives mainly from the study on a few prokaryotes fungi and the higher plants. Over the last ten years rapid progress has been made on the cloning of genes encoding enzymes of the carotenoid pathway using several different approaches. The availability of such a variety of cDNA and genomic clones provides an opportunity to assess the link between the carotenoid pathway genes and other naturally occurring phenotypes with economical relevance. This genetic information could be employed to identify and map carotenoid genes across distinct crop species. Positional (map-based) and insertional mutagenesis approaches are expected to play important role also in the isolation of regulatory genes involved in carotenoid accumulation and metabolism. It is important to highlight that the modification in the patterns of transcriptional regulation has been the most relevant strategy employed by molecular breeders so far. Isolation and characterization of individual alleles of genes involved in the carotenoid pathway are fundamental steps to the success of such an approach. The determination of the rate-limiting reactions(s) in carotenoid biosynthesis has thus far yielded species-specific results. This implies that associations between certain genes and phenotypes in one given plant species may not follow the same pattern in a distinct crop species.