what are plastids ?

What are plastids?

Plastide is a membrane-bound organelle found in plant cells, algae, and some other eukaryotic organisms. They are considered endosymbiotic cyanobacteria, related to Gloeomargarita. The plastids were found and named by Ernst Haeckel, however A. F. W. Schimper was the first to give a reasonable definition. Plastids are the site of manufacture and storage of important chemical compounds used by autotroph eukaryotic cells. They often contain pigments used in photosynthesis and the types of pigments in a plastid determine the color of the cell. They have a common evolutionary origin and have a double-stranded DNA molecule that is circular, like that of prokaryotic cells.

plastids and its type

Plastids containing chlorophyll can carry out photosynthesis and are called chloroplasts. Plastids can also store products such as starch and can synthesize fatty acids and terpenes, which can be used to produce energy and as a raw material for the synthesis of other molecules. For example, the components of the cuticle of the plant and its epicuticular wax are synthesized by epidermal cells from palmitic acid, which is synthesized in the chloroplasts of mesophilic tissue. In plants, plastids can be differentiated in several ways, depending on the role they play in the cell. On the basis of the function, plastids are categories into three categories. Following are the types of plastids:-

Chromoplasts

Luecoplasts

Chloroplasts

 ORIGIN OF PLASTID

Plastids are thought to be endosymbiotic cyanobacteria. This primary endosymbiosis event occurred about 1.5 billion years ago [12] and allowed eukaryotes to carry out oxygenated photosynthesis. [13] Since then, three evolutionary lineages have emerged in which plastids are named differently: chloroplasts in green algae and plants, rhodoplasts in red algae and muroplasts in glaucophytes. Plastids differ in both their pigmentation and their ultrastructure. For example, chloroplasts in plants and green algae have lost all phycobilisomes, light-collecting complexes found in cyanobacteria, red algae, and glaucophytes, but instead contain stroma and grana thylakoids. Glaucocisitophobic plastide, in contrast to chloroplasts and rhodoplasts, is still surrounded by the remains of the cyanobacterial cell wall. All these essential plastids are encompassed by two films.

Complex plastids begin with a secondary endosymbiosis (where a eukaryotic organism engulfs another eukaryotic organism that contains a primary plastid that results in its endosymbiotic fixation), [14] when a eukaryotic engulfs a red or green alga and retains algae plastide, which is usually surrounded by more than two membranes. Now and again, these plastids might be decreased in their metabolic and/or photosynthetic limit. Algae with complex plastids derived from the secondary endosymbiosis of a red algae include heterocontes, haptophytes, cryptotomones, and most dinoflagellates (rhodoplasts). Those who endosymbioses green algae include euglenids and chlorarachniophytes (chloroplasts). Apicomplexa, an edge of obligate parasitic protozoa that include the causative agents of malaria (Plasmodium spp.), Toxoplasmosis (Toxoplasma gondii) and many other human or animal diseases also harbor a complex plastid (although this organelle has been lost in some apicomplexan). like Cryptosporidium parvum, which causes cryptosporidiosis). The 'apicoplast' is no longer capable of photosynthesis, but it is an essential organelle and a promising target for the development of antiparasitic drugs.