Chromoplasts (from ancient Greek χρῶμα chroma “color” and ancient Greek πλαστός plastós “shaped”) are plastids that contain xanthophylls or carotenes and color the parts of the plant in which they occur yellow, orange or red (instead of green like the chloroplasts ). They do not carry out photosynthesis and serve to attract animals (for pollen transfer and seed distribution) or come from aging (as with red tomatoes). Sometimes, however, they have no ecological benefit, as is the case with the carrot , whose orange color cannot attract animals underground. The chromoplasts are responsible for many flower colors and the colors of some fruits or roots , such as red or yellow peppers or carrots . The chromoplasts of the petals and of fruits can arise from leukoplasts or young chloroplasts. Like all plastids, they contain circular DNA in several copies and thus the complete plastome. In addition, they carry out special synthesis activities (e.g. pigment synthesis), but no longer have any chlorophyll and are therefore photosynthetically inactive. With the exception of this, the chromoplasts of some plants also contain small amounts of chlorophyll ( e.g. brown algae ). Chromoplasts, like chloroplasts , are more soluble in fat than in water .
Different types of chromoplasts are distinguished on the basis of certain carrier structures to which the carotenoids (carotenes and xanthophylls) are bound:
- Globular type : It contains lipid globules (diameter 0.2–1 µm) in which the pigments are concentrated. They correspond to the plastoglobules.
- Tubular type : The chromoplasts look like tubes under the electron microscope, but are thread-like liquid crystals that are surrounded by a shell of lipids and the protein fibrillin.
- Crystalloid type : These have a rectangular or rhombic structure, but only consist of 20–45% beta- carotene .
- Membranous type : The pigments are carried by membranes, which are nested in one another in the form of numerous concentric hollow spheres.
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