What is Chromoplast?

Meaning of Chromoplast

Chromoplasts are plastids specialized in the synthesis and storage of different accessory pigments of chlorophyll. These organelles are found in photosynthetic eukaryotic cells, almost exclusively in plants.

It is the chromoplasts (in addition to the chloroplasts) that give color to plant tissues, being found in leaves, roots, fruits and aged flowers, being able to synthesize carotenoids (orange), xanthophylls (yellowish), lycopenes (red) and a series of others. pigments.

They are associated with photosynthesis. (which serve as auxiliary pigments to capture light), leaf senescence, flower color and fruit ripening.

These structures are thought to have evolved differently in angiosperms in a process of co-evolution with pollinating animals. The vibrant colors of flowers and fruits, in addition to their aromas and sugars, serve to attract a greater number of consumers, increasing the chances of seed dispersal.

This coevolution mechanism is so specific that a pattern was observed between the color of the flower and the main pollinator that visits it. White flowers attract beetles more, bluish and purple flowers mainly attract bees while red and yellow flowers seem to be more effective with butterflies.

When found in portions not associated with pollination, such as in roots and tubers, the chromoplast has the function of accumulating insoluble compounds, as occurs with the large store of carotenoids in carrots.

The process of leaf fall in autumn and winter in deciduous plant species shows the presence of chromoplast in the leaves.

With the onset of the colder seasons, the leaves go into senescence, degrading the chlorophyll in the chloroplasts, leaving mostly carotenoids, which depending on the concentration can color the leaves brown, yellow, or orange.

In general, there are five types of chromoplast that refer to their internal organization.

The first type has a globular organization, the second contains pigment crystals (called crystalline), the third is characterized as fibrillar, the fourth is tubular, and the fifth is classified as membranous.

These structures are not seen in plastids, and occur only after their differentiation into chromoplast.

Two or more distinct types may occur in the same portion of the plant body, whereas in other plant tissues there is a predominance of one of them (as in mangoes, which contain many globular chromoplasts).

In some special cases, the same chromoplast can have more than one type of internal composition, as occurs in tomatoes, whose chromoplasts have crystals of lycopene (red pigment) and a membranous structure.

Scientific research associated with the production of carotenoids in plants has identified the genes responsible for the biosynthesis of this molecule.

The color of ripe orange, for example, is due to the accumulation of carotenoids in the chromoplast, indicating that the fruit is ripe.

Tomato flowers, commonly yellow, have a white recessive variety that has one of the genes for carotenoid synthesis modified. The white flower is less visited by the typical tomato pollinators, being less desired in agriculture.

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