Kromoplastid

Kromoplastid, or chromoplasts in English, are plastids that specialize in pigment synthesis and storage in plants and some algae. Unlike chloroplasts, chromoplasts are non-photosynthetic and accumulate carotenoids, giving tissues a yellow, orange, or red coloration.

Chromoplasts arise during development from proplastids or by transformation of existing plastid types, such as chloroplasts, in tissues like ripening fruit or flowering petals. During this transition, chlorophyll degrades and the internal membranes reorganize, while carotenoid synthesis increases and pigments accumulate in plastids.

Primary roles include attracting pollinators and seed dispersers through vivid coloration, protecting tissues from photooxidative stress via carotenoids, and supplying precursors to vitamin A in certain plants.

Anatomically, chromoplasts typically have reduced thylakoid membranes and numerous plastoglobuli, with carotenoids stored in membranes and lipid droplets. They may also contain other pigments such as xanthophylls.

Chromoplasts are widespread in ornamental flowers and in ripe fruits (e.g., peppers, tomatoes, citrus), and their development is a key aspect of fruit ripening and flower coloration. Understanding chromoplast differentiation has implications for agriculture and nutrition.