Chromoplast

Source: Wikipedia, the free encyclopedia.
The coloration of the petals and sepals on the bee orchid is controlled by chromoplasts.

Chromoplasts are

prokaryotes.[2]

Function

Chromoplasts are found in

chloroplasts to chromoplasts in ripening
is a classic example.

They are generally found in mature tissues and are derived from preexisting mature plastids. Fruits and flowers are the most common structures for the biosynthesis of carotenoids, although other reactions occur there as well including the synthesis of sugars, starches, lipids, aromatic compounds, vitamins, and hormones.

cytosine methylation.[3]

Chromoplasts synthesize and store pigments such as orange

sweet potatoes
. They allow the accumulation of large quantities of water-insoluble compounds in otherwise watery parts of plants.

When

leaves change color in the autumn, it is due to the loss of green chlorophyll, which unmasks preexisting carotenoids. In this case, relatively little new carotenoid is produced—the change in plastid pigments associated with leaf senescence
is somewhat different from the active conversion to chromoplasts observed in fruit and flowers.

There are some species of flowering plants that contain little to no carotenoids. In such cases, there are plastids present within the petals that closely resemble chromoplasts and are sometimes visually indistinguishable.

flavonoids located in the cell vacuoles are responsible for other colors of pigment.[1]

The term "chromoplast" is occasionally used to include any plastid that has pigment, mostly to emphasize the difference between them and the various types of leucoplasts, plastids that have no pigments. In this sense, chloroplasts are a specific type of chromoplast. Still, "chromoplast" is more often used to denote plastids with pigments other than chlorophyll.

Structure and classification

Using a

amorphous
pigment granules. The third type is composed of protein and pigment crystals. The fourth type is a chromoplast which only contains crystals. An electron microscope reveals even more, allowing for the identification of substructures such as globules, crystals, membranes,
tubules. The substructures found in chromoplasts are not found in the mature plastid that it divided from.[2]

The presence, frequency and identification of substructures using an electron microscope has led to further classification, dividing chromoplasts into five main categories: Globular chromoplasts, crystalline chromoplasts, fibrillar chromoplasts, tubular chromoplasts and membranous chromoplasts.

carrots which have crystalline chromoplasts.[4]

Although some chromoplasts are easily categorized, others have characteristics from multiple categories that make them hard to place. Tomatoes accumulate carotenoids, mainly lycopene crystalloids in membrane-shaped structures, which could place them in either the crystalline or membranous category.[3]

Evolution

butterflies are often attracted to warmer colors like yellows and oranges.[5]

Research

Chromoplasts are not widely studied and are rarely the main focus of scientific research. They often play a role in research on the tomato plant (

xanthophylls violaxanthin and neoxanthin.[6]

Carotenoid biosynthesis occurs in both chromoplasts and

leaves, which results in the production of the carotenoid lutein.[6]

White flowers are caused by a recessive allele in tomato plants. They are less desirable in cultivated crops because they have a lower pollination rate. In one study, it was found that chromoplasts are still present in white flowers. The lack of yellow pigment in their petals and anthers is due to a mutation in the CrtR-b2 gene which disrupts the carotenoid biosynthesis pathway.[6]

The entire process of chromoplast formation is not yet completely understood on the molecular level. However, electron microscopy has revealed part of the transformation from chloroplast to chromoplast. The transformation starts with remodeling of the internal membrane system with the

photosynthetic activity.[3]

In oranges, the synthesis of carotenoids and the disappearance of chlorophyll causes the color of the fruit to change from green to yellow. The orange color is often added artificially—light yellow-orange is the natural color created by the actual chromoplasts.[7]

Valencia oranges

Citris sinensis L are a cultivated orange grown extensively in the state of Florida. In the winter, Valencia oranges reach their optimum orange-rind color while reverting to a green color in the spring and summer. While it was originally thought that chromoplasts were the final stage of plastid development, in 1966 it was proved that chromoplasts can revert to chloroplasts, which causes the oranges to turn back to green.[7]

Compare plastids

References

  1. ^
    PMID 33874084
    .
  2. ^
    PMID 8522420. {{cite book}}: |journal= ignored (help
    )
  3. ^
    PMID 20801922
    .
  4. PMID 16881676
    .
  5. JSTOR 2265575
    .
  6. ^
    PMID 16816137
    .
  7. ^
    S2CID 83565950
    .

External links
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