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Chromoplast

What is a Chromoplast

Chromoplast is a type of pigmented plastid found exclusively in plant cells.In Greek ‘chroma’ means ‘color’, thus giving this plastid its name. It contains certain pigments that impart color to non-green parts of a plant, such as, fruits and flowers.

Chromoplast

Location: Where is it Found in a Plant Cell

At the cellular level, chromoplasts are located in the cytoplasm of plant cells. They aggregate mostly in the colored but non-green parts of a plant, such as, fruits, flowers, and in certain colored vegetables, such as, carrot, beetroot, and pumpkin.

Characteristics

  • Chromoplasts contain a special pigment called carotenoids.
  • They possess plastoglobules and carotenoid-lipoprotein substructures, which store specific carotenoid pigments and specific lipoprotein fibrils.
  • Carotenoids are of two types: carotene and xanthophylls. Carotene is orange or red, whereas xanthophyll is yellow.
  • Carotenes are composed of carbon and hydrogen. An example of carotene is lycopene. In xanthophylls, oxygen is present. Fucoxanthin and lutein are two examples of xanthophylls.
  • These plastids lack chlorophyll.
  • Chromoplasts may develop from green chloroplasts. For instance, during the ripening of fruits, chlorophyll and thylakoid membranes degrade, and carotenoids are accumulated. Thus, the chromoplasts are formed.
  • Some chromoplasts may transform back to chloroplasts. For instance, chromoplasts of some plants like carrot root, citrus fruit, pumpkin, and cucumber lose carotene and develop chlorophyll and thylakoid system again. This redifferentiation is promoted by two plant hormones, gibberellin, and nitrates.
  • During the transformation of these chromoplasts, the plastid DNA remains unchanged, but ribosomes and rRNA disappear.
  • Light, temperature, and nutrients are the key factors in the formation of chromoplasts.
  • Chromoplast development is irreversible in plants like pepper and tomato
  • Chromoplasts can also be derived from leucoplasts, e.g., watermelon, papaya, carrot, mango, etc.

Types with Structure

Chromoplasts vary in structural appearance. Based on the carotenoid bearing components, they are generally grouped into five types: (1) globular, (2) membranous, (3) tubular, and (4) crystalline.

1. Globular

It consists of plastoglobuli, bearing carotenoid pigments. They are often concentrated in the peripheral stroma.

Examples: Petals of Ranunculus repens, yellow fruits like capsicum, perianth of citrus fruits.

2. Membranous

 Carotene pigments are present in about 20 concentric membranes.

Examples: Petals of Citrus sinensis, daffodils, tulip.

3. Tubular

Lipoprotein tubules contain carotenoids.

Examples: Red capsicum rose.

4. Crystalline

Here, pure carotene remains embedded as crystals.

Examples: Carotene in carrot roots, lycopene in tomato.

Functions

  • As they impart vibrant colors to various plant parts, they help attract animals and insects for cross-pollination and dispersal of seeds.
  • Carotenoids act as antioxidants.
  • Beta-carotene found in carrots is a precursor of vitamin A.
  • Dietary carotenoids reduce the risk of cardiovascular diseases and cancer.
  • Fucoxanthin is proven to have anti-diabetic and anti-obesity effects.

Chromoplast vs Chloroplast

Though both chromoplast and chloroplast are pigmented plastids, they also have some differences.

Differences

ChromoplastChloroplast
Contains carotenoidsContains chlorophyll
Found in non-green parts of a plant, such as, petals of flower, ripening fruits, and aging leaves.Found in the green parts of a plant, such as, leaves and young stem.
Does not contain a lamellar system.Contains a lamellar system.
Does not contain ribosomes.Contains 70S ribosomes.
Helps in cross-pollination and seed dispersal.Helps in photosynthesis.

Similarities

  • Contain pigments
  • Remains surrounded by two membranes
  • Contain identical DNA
  • Divide by binary fission
  • Occur in the exposed parts of the plant

Article was last reviewed on Monday, December 27, 2021

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