Chromoplast

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Chromoplasts are pigment-containing plastids in some plants. They likely descended from other plastids like chloroplasts. They give color to fruits, flowers, some roots, and aging leaves by accumulating carotenoids (orange, yellow, red). In ripening fruit, chloroplasts often convert to chromoplasts, boosting pigment production.

Chromoplasts also store various compounds and help attract pollinators and seed dispersers. Tomato lycopene makes red flesh; yellow flower colors come from xanthophylls such as violaxanthin and neoxanthin. Carotenoids are made in both chromoplasts and chloroplasts. Some species have little carotenoid.

The term chromoplast is sometimes used broadly for any pigment-containing plastid, but it usually refers to plastids with carotenoids rather than chlorophyll. Under light microscopy chromoplasts resemble four basic types; electron microscopy expands this to five main forms: globular, crystalline, fibrillar, tubular, and membranous. Different types can coexist in one organ, e.g., mangoes (globular) and carrots (crystalline); tomatoes may show crystalline or membranous forms.

Chromoplast formation begins with remodeling of the chloroplast: membranes reorganize, thylakoids break down, and new membranes form to support carotenoid crystals. Chlorophyll declines, stopping photosynthesis. The orange color of ripe oranges comes from these pigments, though breeders sometimes enhance it; chromoplasts can revert to chloroplasts, turning fruit green again in spring.