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Plastid in Plants


What is plastid in plants?

A special organelle has been identified in the cells of plants and algae. It is a membrane-bound organelle found in certain eukaryotic organisms as well.

The plastids are generally called the intracellular endosymbiotic Cyanobacteria because of the distinguishing characteristic displayed by the organelle. The common examples of plastid include the chloroplast, which is needed for photosynthetic purposes, and chromoplast, which is another significant pigment required for synthesis purposes. Leucoplast is also an example of the plastid in plants.

History of the organelle

The scientists believe that the plastid and Cyanobacteria were due to the endosymbiosis of the Archaeolastida. The event almost dates back to the time 1.5 years ago, and the event was observed in the genus Gleoemargarita.

Later, the botanists also found that a similar event occurred in another species called the photosynthetic Paulinella amoeboid. This event was recorded much later than the first one, around ninety to one forty million years ago.

Secondary and tertiary endosymbiosis was also observed in other plant species. The ingestion of plastids is called kleptoplasty.

Discovery of the organelle

It is believed that Ernst Haekel was the discoverer of the organelle, and he was the one who named the organelle "plastid." However, A.F.W Schimper was the scholar who provided a clear definition of the organelle and described the structure. They studied the pigments present in the plastid, and it was observed that the color of the plant was determined by the pigment present in the plastid.

The chemical substances synthesized here are responsible for the autotrophic activity of the plant and help in energy production. The plastids are said to possess double-stranded DNA material, which is circular. This resembles the circular chromosome of prokaryotic organisms.

Development in land plants

Now we shall discuss the growth and development of plastid in the land plants.

  • Chloroplasts

    The chlorophyll-containing plastids in land plants can carry out the process of photosynthesis. These are then named the chloroplasts. The process of photosynthesis is required for the production of energy and food for the plant as well as important for the other species in the food chain.

  • Other molecules in chloroplasts

    Organelles in land plants are also responsible for storing the excess glucose produced in the form of starch. Fatty acids and terpenes are also stored as raw materials for the plant to process later. The epicuticular wax and the components of the cuticular layer is produced from epidermal cells of palmitic acid in the chloroplast present in the mesophyll layer.

  • Origin of plastid

    All the plastids produced in the plants is derived from the proplastids, which are in turn available in the meristematic tissue of the plants. The younger chloroplasts and the proplastid can divide by the process of binary fission, and even some of the mature chloroplasts bear the capacity to do so.

    The proplastids are further differentiated into many kinds which are responsible for different functions in the plants. Let us check them out.

  • Chloroplasts

    This is the plastid which is specialized to bear the green pigments chlorophyll responsible for the production of energy and oxygen. It is formed from the precursor known as the etioplasts.

  • Chromoplast

    These are the colored plastids that are responsible for the production of other pigments and vital synthesis.

  • Gerontoplasts

    These are highly crucial for the dismantling of the chlorophyll pigment from the plant during the process of senescence and death.

  • Leucoplasts

    These plastids are colorless and are responsible for the production of monoterpene. It is further classified into the following categories for specialized purposes.

Amyloplasts are required for the storage of fat and the detection of gravitational pull. Elaioplast for the storage of fat and the proteinoplast helps to modify the structure of protein and store them. The endosomes are required for the production of tannin and polyphenols.

The plastids bear the ability to interconvert between these forms according to the requirements of the cell and the differentiation process.

What is the contribution of plastid for DNA repair?

The plasmid DNA is prone to damage and requires repair, just like the maize seedling. The oxidative environment is responsible for the damage because of the photo-oxidative reaction. The DNA repair proteins are encoded by the cell genome, which is then translocated to the plastid for further damage control.

Genome stability is maintained by requiring the DNA that is present within the plastid.

Thus the plastid takes significant responsibilities in maintaining the DNA and initiating repair from time to time.





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