Metabolic Engineering of Carotenoid Formation in Carrot Roots

Carotenoids, a large class of yellow, orange and red pigments accumulate in the chloroplasts of leaves or in the chromoplasts of many flowers and fruits as well as carrot roots. In plants, carotenoids function as

Carotenoids, a large class of yellow, orange and red pigments accumulate in the chloroplasts of leaves or in the chromoplasts of many flowers and fxuits as well as carrot roots. In plants, carotenoids function as accessory pigments in photosynthesis, eolourants in flowers, fxuits and roots, biosynthesis of abseisie acid （ABA）, an important regulator of plant growth. In photosynthetic tissue, the dominant function of carotenoids is the quenching of the triple chlorophyll as a mechanism to protect the photosynthetic apparatus. Carotenoids exert protective functions due to their high antioxidative potential and also important components of the human diets. Since humans and animals are unable to synthesize earotenoids de novo, they must rely upon dietary earotenoids. Different earotenoids have different beneficial effects in human body. All earotenoids （e.g. alpha-carotene, beta-carotene and beta-eryptoxanthin） that contain a beta-ring can be converted to retinol and are thus precursors for vitamin A in human and animal diets. Because of the epsilon ring, alpha-carotene has only half the provitarnin A activity compared to that of beta-carotene. Therefore, it is after lyeopene formation that carotenoid biosynthetic pathway diverges and produces either more or less provitarnin A activity carotenoid,