Abstract
Plastids have many differentiation states, including proplastids, chloroplasts, amyloplasts, etioplasts, gerontoplasts, and chromoplasts. These various forms of organelles play very different roles and are mostly interconvertible. An exception is gerontoplasts, the terminal state of chloroplasts in senescent leaves. Chromoplasts are plastids in which exceptional amounts of carotenoids accumulate. As a consequence, chromoplasts confer bright colors to plant tissues: shades of orange, yellow, and red. Chromoplasts, therefore, are the quintessential plastids of flowers and fruits, attracting insects for pollination and animals for seed dispersal. Chromoplasts may originate from chloroplasts, proplastids, or leukoplasts. The accumulation of carotenoids is independent of the presence or absence of chlorophyll. The function of chromoplasts is esthetic, making plant organs attractive to animals, such as humans. Therefore, they are not essential to the life of the plant. Chromoplast carotenoids have provided a rich substrate for organic chemistry with many chemical species serving as botanical species markers.