Plastid NEW.pptx

plastids origin structure function and all details

1. PRESENTATION ON “ Plastids ” COURSE TITLE : Cell Biology and Molecular Genetics COURSE NO. : GP-508

2. What are the plastids ? Basics about plastid Types and Functions ? Information about all the types of Plastids with Functions ? Endosymbiotic Theory ? Characteristics of Plastid DNA? DNA replication in Plastids ? Some Case Study on Plastid

3. What are the Plastids ? The plastid is  a membrane-bound organelle found in the cells of plants, algae , and some other eukaryotic organisms. They often contain pigments used in photosynthesis, and the types of pigments in a plastid determine the cell's color. Discovered and Named By Ernst Haeckel in 1866 Defined By Andreas Franz Wilhelm Schimper in 1883

4. Some Characters of Plastids Major Organelle of Plant and algal cells Site of manufacture and storage of important chemical compounds Has circular, dsDNA copies Replicates autonomously of the cell Thought to have been originated from endosymbiotic bacteria. They often contain pigments used in Photosynthesis The types of pigments in a plastid determine the cells Colour They have a common evolutionary origin and posses a double-Stranded DNA molecule that is Circular, like that of prokaryotic cells.

5. Pigment Synthesis and storage of glucose Contain carotenoids (R,Y, O pigments) Synthesis of fatty acids and Amino acids Storage of Starch and Sugars Sites of Enzyme(Protein) Activity Storage of Lipids and Oils 2) Basics about plastid Types and Functions ?

6. Chloroplast Chloroplasts are found in all higher plants. It is oval or biconvex, found within the mesophyll of the  plant cell .  The size of the chloroplast usually varies between 4-6 µm in diameter and 1-3 µm in thickness. They are double-membrane organelle with the presence of outer, inner and intermembrane space. There are two distinct regions present inside a chloroplast known as the grana and stroma. Grana are made up of stacks of disc-shaped structures known as thylakoids. The grana of the chloroplast consists of chlorophyll pigments and are the functional units of chloroplasts. Stroma is the homogenous matrix which contains grana and is similar to the cytoplasm in cells in which all the organelles are embedded. Stroma also contains various enzymes, DNA, ribosomes, and other substances. Stroma lamellae function by connecting the stacks of thylakoid sacs.

7. Membrane Envelope It comprises inner and outer lipid bilayer membranes. The inner membrane separates the stroma from the intermembrane space. Intermembrane Space The space between inner and outer membranes. Thylakoid System The system is suspended in the stroma. It is a collection of membranous sacs called thylakoids. The green coloured pigments called chlorophyll are found in the thylakoid membranes. It is the sight for the process of light-dependent reactions of the  photosynthesis  process. The thylakoids are arranged in stacks known as grana and each granum contains around 10-20 thylakoids. Stroma It is a colourless , alkaline, aqueous, protein-rich fluid present within the inner membrane of the chloroplast present surrounding the grana. Grana These are the sites of conversion of light energy into chemical energy. Chlorophyll It is a green photosynthetic pigment that helps in the process of photosynthesis.

8. They are located in the cell cytoplasm and move across the cell  cytoplasm  along with the cellular fluids. The  DNA  is also found in organelles mitochondria and chloroplast. The circular DNA of chloroplast is referred to as cpDNA . Chloroplasts are differentiate from other types of plastids by their green colour , which results from the presence of two pigments,  chlorophyll   a  and  chlorophyll   b . A function of those pigments is to absorb light energy for the process of  photosynthesis . Other pigments, such as  carotenoids and serve as accessory pigments, trapping  solar energy  and passing it to chlorophyll.

9. Chemical Constituents Percent dry Weight Components Protein 35-55 % Insoluble 80% Lipids 20-30 % Fats 50% , Sterols 20%, Wax 16% , Phosphatides 2-7% Carbohydrates Variable Starch, Sugar, Phosphates 3-7% Chlorophyll 9.0 Chlorophyll a 75% Chlorophyll b 25% Carotenoids 4.5 Xanthophyll 75% Carotene 25% Nucleic acids RNA DNA 3-4 <0.02-0.1 Chemical Composition of Chloroplast

10. Chromoplasts Chromoplasts are brightly colored plastids that act as the site of pigment accumulation. found fleshy fruits, flowers as well as various other pigmented parts of the plant such as leaves. The plastids play an important role in pollination they act as visual attractors for animals and other pollinators involved in pollination. chromoplasts vary significantly depending on the type of carotenoids that they contain.

11. Parameters Tubules A) Chemicals Proteins % 45 Lipids % 55 Protein/ Lipids Ratio 1:1:22 Chemical Composition Chromoplasts synthesize and store pigments. such as, orange  carotene , yellow  xanthophylls , and various other red pigments. As such, their color varies depending on what pigment they contain. However, they are also found in roots such as  carrots  and  sweet potatoes . They allow the accumulation of large quantities of water-insoluble compounds in watery parts of plants.

12. There are two types of chromoplasts which include:   Phaeoplast ( green algae and plants) : This type of plastid is found in brown algae. Phaeoplast is Yellow or Brown in colour . It contains a carotenoid pigment called Fucoxanthin. Its main function absorbs light and transfer the energy to chlorophyll a and masks the colour of chlorophyll a, which is also present. Rhodoplast (red algae) : This type of plastid is found in red algae.   Rhodoplast is red in colour ( rhode = red; plast = living). It contains a red pigment called phycoerythrin. Its main function is  to absorb light .

13. Gerontoplasts Gerontoplasts are formed during  sensecence The senescent phase is  the period after reproductive phase , when a cell loses its ability to reproduce . senescence involves the degradation of various organelles of a plant cell. During   sensecence process, the chloroplast undergoes extensive structural modification of the thylakoid membrane followed by the formation of increased numbers of plastoglobuli. The main function of plastoglobuli as  stores for plastidic lipids. This plastid play an important role in controlled degradation of the chloroplasts.

14. Leucoplasts Leucoplasts do not have any pigment. Lacking  photosynthetic pigments , leucoplasts are not green. They located in non-photosynthetic tissues of plants, such as  roots ,  bulbs  and  seeds .  They are responsible for storing food related items for the plant, like lipids, proteins, and starches.  Additionally, leucoplasts can be responsible for synthesizing amino acids and fatty acids. Leucoplast also involved in the biosynthesis of palmitic acid and certain amino acids.

15. The following are the three major types of leucoplasts: Amyloplasts Elaioplast ( Lipoplasts ) Proteinoplasts

16. Amyloplasts The word " Amylo " means starch. Plastid involved in long term storage of starch. Amyloplasts play an important role in the storage of starch . Compared to some of the other plastids, amyloplasts have very little internal membrane and contain one or several larger grains.

17. Elaioplast ( Lipoplasts ) The word " Elaiov " is a Greek word for olive. They serve to store oils and lipids which explain the small drops of fat found inside the plastids. Structure-wise, elaioplasts do not have specific internal structures. only lipids/oil droplets (plastoglobuli) are present. Elaioplasts are have small and spherical shape. They are rare when compared to the other plastids. Elaioplasts are found in the tapetal cells ( A layer of nutritive cells within the sporangium , providing nutrition for growing spores of flowering plants.) of some plants where they contribute to the maturation of the pollen wall.

18. Proteinoplasts Article By: Dey PM, Brownleader MD, Harborne JB (1997-01-01) Proteinoplasts contain higher levels of protein as compared to the other plastids. These proteins are also large enough to be seen under the  light microscope . The proteins either accumulate as amorphous or crystalline inclusions and bound by a membrane. Proteinoplasts (sometimes called  proteoplasts ,  aleuroplasts , and  aleuronaplasts ) are specialized   organelles   found only in  plant cells .

19. Origin of Plastids : Plastids are thought to be  endosymbiotic   cyanobacteria . A scientist named Lynn Margulis put all of this information together and published Endosymbiotic Theory in 1967 . The Endosymbiotic Theory states that  the mitochondria and chloroplast in eukaryotic cells were once aerobic bacteria (prokaryote) that were ingested by a large anaerobic bacteria   (prokaryote) . Symbiosis = It is occurs when two different species benefit from living and working together.

20. SOOO… How did it happen? Endosymbiotic theory describes how a large host cell and ingested bacteria could easily become dependent on one another for survival, resulting in a symbiotic relationship Eventually, the smaller prokaryotes that had been engulfed adapted and evolved into some of the organelles we know of today in eukaryotic cells like the mitochondria and chloroplasts . Over millions of years of evolution, mitochondria and chloroplasts have become more specialized and today they cannot live outside the cell.

21. A A prokaryote ingested some aerobic bacteria. These bacteria were protected by the prokaryote and produced energy for it. B Over a long period of time, these bacteria became mitochondria, and could no long live on their own. C Some prokaryotes ingested some cyanobacteria which contained photosynthetic pigments. D Over time, the cyanobacteria became chloroplasts and could no longer live on their own.

22. Similarities between mitochondria, chloroplasts, and prokaryotes … Circular DNA Ribosomes Binary fission

23. Chloroplast genome Chloroplast DNA ( cpDNA ) is also known as plastid DNA ( ptDNA ). Circular double stranded DNA molecule Ct genomes are relatively larger 140kb in higher plants, 200kb in lower eukaryotes. cpDNA regions includes Large Single-Copy (LSC) & Small Single-Copy (SSC) regions, and Inverted Repeats (IRA & IRB). Variation in length mainly due to presence of inverted repeat (IR) Conifers and a group of legumes lack Inverted Repeats. Characteristics of Plastid DNA (Chloroplast)

24. D Loop ( Chloroplast DNA Replication )

25. Non- mendelian inheritance. Self replication Somatic segregation in plants Inherited independently of nuclear genes Conservative rate of nucleotide substitution enables to resolve plant phylogenetic relationships at deep levels of evolution. eg. familial level; mono- dicotyledonous PROPERTIES of ctDNA

26. THE EFFE T OF LEAD ON THE STRUCTURE AND FUNCTION OF WHEAT PLASTIDS Case Study The purpose of this research was to study the fine structure, the pigment content, and the photosynthetic activity of plastids of etiolated and green leaves held for several days on water containing lead salts. Material and Methods Total chlorophyll, total carotenoids and photosynthetic activity of etiolated leaves maintained 48 h in light on water and PbCl2. Total chlorophyll, total carotenoids and photosynthetic activity of green leaves maintained 48 h in light on water and PbCl2. MERCEDES WRISCHER and DARINKA MEGLAJ (1980)

27. Total chlorophyll (mg/g fr. wt.) Total carotenoids (mg/g fr. wt.) Hill reaction ( M 0.2/mg chlorophyll/h) Photosystem 1 activity ( M O2/mg chlorophyll/h) Water 0.90 0.14 109.53 78.52 PbCl2 5 mM 0.46 0.11 98.86 115.90 Total chlorophyll (mg/g fr. wt.) Total carotenoids (mg/g fr. wt.) Water 0.90 0.14 109.53 78.52 PbCl2 5 mM 0.46 0.11 98.86 115.90 Total chlorophyll, total carotenoids and photosynthetic activity of etiolated leaves maintained 48 h in light on water and PbCl2. Total chlorophyll, total carotenoids and photosynthetic activity of green leaves maintained 48 h in light on water and PbCl2. Total chlorophyll (mg/g fr. wt.) Total carotenoids (mg/g fr. wt.) Hill reaction ( M 0 2/mg chlorophyll/h) Photosystem 1 activity( M O2/mg chlorophyll/h) Water 1.29 0.14 41.55 61.76 PbCl2 5 mM 0.82 0.14 37.94 33.08 Total chlorophyll (mg/g fr. wt.) Total carotenoids (mg/g fr. wt.) Water 1.29 0.14 41.55 61.76 PbCl2 5 mM 0.82 0.14 37.94 33.08 Result

28. The investigations have shown that in plastids of etiolated leaves, after they were exposed to light, the development of new thylakoids and the synthesis of pigments, especially of chlorophyll are strongly affected by lead salts ( PbCl , or PbCl2 at concentration of 1 mM or 5 mM). In relation to their low chlorophyll content, the photosynthetic activity (both the Hill reaction, and the activity of photosystem 1) in these plastids is rather high. This indicates that lead inhibits the norm al differentiation of plastids so that they remain in their early etiochloroplast developmental stage. There are no prominent ultrastructural changes in the chloroplasts of green leaves held on lead solutions, although their chlorophyll content and photosynthetic activity are lower than in chloroplasts of untreated leaves. It has been shown that, when isolated chloroplasts are treated with lead salts, photosystem 1 is less affected than the Hill reaction. Some other ultrastructural changes found in leaves held on lead solutions are also described. Summary

29. Case Study DNA replication in chloroplasts Chloroplasts contain multiple copies of a DNA molecule (the plastome ) that encodes many of the gene products required to perform photosynthesis. The plastome is replicated by nuclear-encoded proteins and its copy number seems to be highly regulated by the cell in a tissue-specific and developmental manner. Sabine Heinhorst and Gordon C. Cannon (1993)

30. Fig. 2. The dual D-loop model for the initiation of chloroplast DNA replication. (A) Unidirectional elongation of nascent strand initiated from both origins. (B) Unidirectional fork movement toward each other. (C) Fusion of D-loops to Cairns-type intermediates. (D) Bidirectional, semi-discontinuous replication. (E) Resulting daughter molecules. The arrows denote the two D loop initiation sites (origins).

31. As evident from the above discussion, the current state of DNA replication studies in chloroplasts is rather a confusing one. Lack of a genetics system in plastids has prevented mutant analysis that has been instrumental in identifying DNA replication enzymes in bacteria and yeast. Our understanding of the biochemical mechanism by which the plastome is replicated and the molecular basis for its regulation is limited. In this review of chloroplast DNA replication and examine current efforts to elucidate its mechanism. Results obtained with diverse plant types and with plastomes of different morphologies do not yet allow us to present a generalized picture of ctDNA replication. Cultures offer the additional potential for manipulation, such as synchronization of plastome replication. Summary

32. References Advances in Plastid Biology and Its Applications By Niaz Ahmad , Steven J. and Brent L. Nielsen (2016) Plastids By Simon G. Moller

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