File Name: the structure and function of plastids .zip
Plastids are a group of phylogenetically and physiologically-related organelles found in all types of plants and algae.
Plastids perform many essential functions in plant metabolism including photosynthesis, synthesis of metabolites, and stress signaling. The most prominent type in green leaves is the chloroplast which contains thylakoids, plastoglobules, and starch. As these structures are closely linked to the metabolism of chloroplasts, changes during plant growth and development and during environmental stress situations are likely to occur. The aim of this study was to characterize changes in size and ultrastructure of chloroplast on cross-sections of leaves during high light stress, Botrytis infection, and dark induced senescence by quantitative transmission electron microscopy TEM.
They are considered to be intracelluar endosymbiotic Cyanobacteria. Examples include chloroplasts used for photosynthesis , chromoplasts used for pigment synthesis and storage , and leucoplasts non-pigmented plastids that can sometimes differentiate. The event to permanent endosymbiosis in the Archaeplastida clade of land plants , red algae , and green algae probably occurred with a cyanobiont a symbiotic cyanobacteria related to the genus Gloeomargarita , around 1.
Plastids were discovered and named by Ernst Haeckel , but A. Schimper was the first to provide a clear definition. They often contain pigments used in photosynthesis , and the types of pigments in a plastid determine the cell's color. They are also the site of manufacture and storage of important chemical compounds used by the cells of autotrophic eukaryotes.
They possess a double-stranded DNA molecule that is circular, like that of the circular chromosome of prokaryotic cells. In land plants , plastids that contain chlorophyll can carry out photosynthesis and are called chloroplasts. Plastids can also store products like starch and can synthesize fatty acids and terpenes , which can be used for producing energy and as raw material for the synthesis of other molecules.
For example, the components of the plant cuticle and its epicuticular wax are synthesized by the epidermal cells from palmitic acid , which is synthesized in the chloroplasts of the mesophyll tissue.
Proplastids and young chloroplasts commonly divide by binary fission , but more mature chloroplasts also have this capacity. Plant proplastids undifferentiated plastids may differentiate into several forms, depending upon which function they perform in the cell. They may develop into any of the following variants: .
Depending on their morphology and function, plastids have the ability to differentiate, or redifferentiate, between these and other forms. Each plastid creates multiple copies of a circular 10— kilobase plastome. The plastome contains about genes encoding ribosomal and transfer ribonucleic acids rRNAs and tRNAs as well as proteins involved in photosynthesis and plastid gene transcription and translation.
However, these proteins only represent a small fraction of the total protein set-up necessary to build and maintain the structure and function of a particular type of plastid. Plant nuclear genes encode the vast majority of plastid proteins, and the expression of plastid genes and nuclear genes is tightly co-regulated to coordinate proper development of plastids in relation to cell differentiation.
Plastid DNA exists as large protein-DNA complexes associated with the inner envelope membrane and called 'plastid nucleoids'.
Each nucleoid particle may contain more than 10 copies of the plastid DNA. The proplastid contains a single nucleoid located in the centre of the plastid. The developing plastid has many nucleoids, localized at the periphery of the plastid, bound to the inner envelope membrane.
During the development of proplastids to chloroplasts, and when plastids convert from one type to another, nucleoids change in morphology, size and location within the organelle.
The remodelling of nucleoids is believed to occur by modifications to the composition and abundance of nucleoid proteins. Many plastids, particularly those responsible for photosynthesis, possess numerous internal membrane layers.
In plant cells , long thin protuberances called stromules sometimes form and extend from the main plastid body into the cytosol and interconnect several plastids. Proteins, and presumably smaller molecules, can move within stromules. Most cultured cells that are relatively large compared to other plant cells have very long and abundant stromules that extend to the cell periphery.
In , evidence of possible plastid genome loss was found in Rafflesia lagascae , a non-photosynthetic parasitic flowering plant, and in Polytomella , a genus of non-photosynthetic green algae. Extensive searches for plastid genes in both Rafflesia and Polytomella yielded no results, however the conclusion that their plastomes are entirely missing is still controversial.
Plastid types in algae and protists include:. The plastid of photosynthetic Paulinella species is often referred to as the 'cyanelle' or chromatophore, and is used in photosynthesis;   it had a much more recent endosymbiotic event about 90— million years ago, and is the only other known primary endosymbiosis event of cyanobacteria. Etioplasts , amyloplasts and chromoplasts are plant-specific and do not occur in algae.
Most plants inherit the plastids from only one parent. In general, angiosperms inherit plastids from the female gamete, whereas many gymnosperms inherit plastids from the male pollen. Algae also inherit plastids from only one parent. The plastid DNA of the other parent is, thus, completely lost. In interspecific hybridisations, however, the inheritance of plastids appears to be more erratic.
Although plastids inherit mainly maternally in interspecific hybridisations, there are many reports of hybrids of flowering plants that contain plastids of the father. Plastid DNA of maize seedlings is subject to increased damage as the seedlings develop. Plastids are thought to be endosymbiotic cyanobacteria. The primary endosymbiotic event of the Archaeplastida is hypothesized to have occurred around 1. The plastids differ both in their pigmentation and in their ultrastructure.
For example, chloroplasts in plants and green algae have lost all phycobilisomes , the light harvesting complexes found in cyanobacteria, red algae and glaucophytes, but instead contain stroma and grana thylakoids. The glaucocystophycean plastid—in contrast to chloroplasts and rhodoplasts—is still surrounded by the remains of the cyanobacterial cell wall. All these primary plastids are surrounded by two membranes.
The plastid of photosynthetic Paulinella species is often referred to as the 'cyanelle' or chromatophore, and had a much more recent endosymbiotic event about 90— million years ago; it is the only known primary endosymbiosis event of cyanobacteria outside of the Archaeplastida.
In contrast to primary plastids derived from primary endosymbiosis of a prokaryoctyic cyanobacteria, complex plastids originated by secondary endosymbiosis in which a eukaryotic organism engulfed another eukaryotic organism that contained a primary plastid.
The Apicomplexa , a phylum of obligate parasitic protozoa including the causative agents of malaria Plasmodium spp. The ' apicoplast ' is no longer capable of photosynthesis, but is an essential organelle, and a promising target for antiparasitic drug development.
Some dinoflagellates and sea slugs, in particular of the genus Elysia , take up algae as food and keep the plastid of the digested alga to profit from the photosynthesis; after a while, the plastids are also digested.
This process is known as kleptoplasty , from the Greek, kleptes , thief. In J. M Whatley proposed a plastid development cycle which said that plastid development is not always unidirectional but is a cyclic process several times. The proplatids are precursor of the more differentiated forms of plastids as shown in the diagram depicted. From Wikipedia, the free encyclopedia. Cell organelle. The Structure and Function of Plastids. Advances in Photosynthesis and Respiration. Springer Netherlands.
Frontiers in Microbiology. Journal of Cell Science. BMC Evolutionary Biology. Kerstiens ed. The Diversity of Plastid Form and Function". Plant Molecular Biology. Advances in Botanical Research. The Scientist.
Retrieved Trends in Plant Science. Biological Sciences. Palenik, B. Journal of Phycology. Proceedings of the National Academy of Sciences. PLOS Currents. Journal of Plant Research. Journal of Experimental Botany. Frontiers in Plant Science. The Plant Journal.
Nature Communications. Bibcode : NatCo Nature Education. The New Phytologist. Plant Physiology Online. Archived from the original on Birky CW Annual Review of Genetics. Archived from the original PDF on Chan CX, Bhattacharya D Bhattacharya D, ed. Origins of Algae and their Plastids.
Annual Review of Plant Biology. Keeling PJ March Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences. Cell wall Extracellular matrix. History of botany. Plant morphology glossary.
In this article we will discuss about:- 1. Types of Plastids in Cell 2. Structure of Chloroplastid 3. Origin 4. The leucoplasts are the colourless plastids principally serving the purpose of storage. On the basis of nature of storage compound, leucoplastids are amyloplasts starch , elaioplasts oil or aleuroplasts protein. The green plastids or chloroplastids are needed for photosynthesis.
Plastid Origin and Development. Front Matter. Pages PDF.
In this article we will discuss about:- 1. Types of Plastids in Cell 2. Structure of Chloroplastid 3. Origin 4. The leucoplasts are the colourless plastids principally serving the purpose of storage.
Plastids are cell organelles present in plants, green and red algae as well as in some non-photosynthetic organisms such as the apicomplexa. Depending on their species- and tissue-specific context they exhibit morphological and biochemical properties of wide variety. In green plant tissues they are the site In green plant tissues they are the site for photosynthesis and important biochemical pathways including sulfur and nitrogen reduction. Despite their heterogeneous appearance all plastid types emerged from one and the same monophyletic endosymbiotic event in which a cyanobacteria-like ancestor was taken up by a heterotrophic, mitochondriated eukaryote.
DOI : During endosymbiogenesis plastids have partially lost their independence, and tight co-regulation between the host nucleus and the organelle has been developed. In this work, the general features and the special characteristics such as plastid morphology, number of plastid bounding membranes, periplastidial space and nucleomorph, thylakoid arrangement, plastid genome, plastid-located storage materials, carboxysomes and pyrenoids, plastoglobuli and eyespots, and other plastid inclusions of the chloroplasts of the most important algal groups are reviewed in details. Several unicellular algae possess only one or a few chloroplast s. In more complex organisms, such as for instance brown algal thalli and land plants, plastid form and function have been diversified and plastids got gradually specialized in parallel with the evolution of cells with different specific functions. Cells that have lost their photosynthetic activity developed special plastid types with less or no chlorophyllous pigments and thylakoids, but with specific functions such as storage leucoplasts or carotenoid synthesis chromoplasts.
They are considered to be intracelluar endosymbiotic Cyanobacteria. Examples include chloroplasts used for photosynthesis , chromoplasts used for pigment synthesis and storage , and leucoplasts non-pigmented plastids that can sometimes differentiate. The event to permanent endosymbiosis in the Archaeplastida clade of land plants , red algae , and green algae probably occurred with a cyanobiont a symbiotic cyanobacteria related to the genus Gloeomargarita , around 1. Plastids were discovered and named by Ernst Haeckel , but A. Schimper was the first to provide a clear definition. They often contain pigments used in photosynthesis , and the types of pigments in a plastid determine the cell's color.
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