Yellow, orange, or red fatsoluble pigments found in all photosynthesizing cells, where they act as accessory photosynthetic pigments. Their absorption spectrum suggests they may also be involved in the phototropic response. They are also found in other organs, e.g. roots, notably carrot roots, and petals. There are two groups of carotenoids; the *carotenes
, which are hydrocarbons, and the *xanthophylls
, which are oxygenated derivatives of the carotenes.
During leaf senescence the carotenoids do not break down as quickly as the chlorophylls and their colours are temporarily revealed.