Plastids are membrane-bound organelles found in plant and algal cells that often contain pigments used in photosynthesis. There are several types of plastids that serve different functions: chloroplasts contain chlorophyll and are the site of photosynthesis; chromoplasts contain carotenoids and synthesize and store pigments; gerontoplasts are involved in chloroplast degradation during senescence; and leucoplasts like amyloplasts, elaioplasts, and proteinoplasts store starches, lipids, and proteins respectively. It is believed that plastids evolved from endosymbiotic cyanobacteria that were engulfed by plant cells and eventually became specialized organelles.

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

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

3. 1. 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. Plastid
Types
Chloroplasts
Chromoplasts
Gerontoplasts
Leucoplasts
1) Amyloplasts
2) Proteinoplasts
3) Elaioplast (Lipoplasts)
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:
I. Amyloplasts
II. Elaioplast (Lipoplasts)
III. Proteinoplasts

16. I. 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. II. 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. III. 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.
4) Characteristics of Plastid DNA (Chloroplast)

25. D Loop ( Chloroplast DNA Replication )

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

28. 1. 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)

29. Total chlorophyll
(mg/g fr. wt.)
Total carotenoids
(mg/g fr. wt.)
Hill reaction
(𝜇M 0.2/mg
chlorophyll/h)
Photosystem 1
activity(𝜇M 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, 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
(𝜇M 0 2/mg
chlorophyll/h)
Photosystem 1
activity(𝜇M O2/mg
chlorophyll/h)
Water 1.29 0.14 41.55 61.76
PbCl2
5 mM
0.82 0.14 37.94 33.08
Result

30. • 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

31. Case
Study
II. 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)

32. 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).

33. • 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

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

35. THANK YOU…