1.
PLASTIDS
Dr. Saji Mariam George
Associate Professor (Retired)
Assumption College Autonomous
Changanacherry

2.
PLASTIDS
• Double membrane bound organelles
• Found free in the cytoplasm
• Shape may vary- spherical, disc –shaped,
elongated etc.
• Self replicating organelles since they possess
DNA and 70 S ribosomes.
• Functions – Synthesis of food , storage of
carbohydrates, proteins and lipids.

3.
The term plastid was used by Schimper(1885)
and classified plastids into three
i. Chloroplasts
ii. Chromoplasts
iii. Leucoplasts

4.
Chloroplasts
• Most important and common plastid- contain
green pigment chlorophyll which can
synthesize starch using CO2 and H2O with the
help of energy derived from sunlight by a
process known as photosynthesis.
• Located mainly in the leaves of higher plants
and in green algae.
• Shape, size, number and distribution vary in
different cells, but are fairly constant for a
given tissue.

5.
Chloroplasts…..
Shape :
• Cup – shaped (Chlamydomonas)

6.
Chloroplasts…..
• Ribbon – shaped and spirally arranged
(Spirogyra)
Image:https://en.wikipedia.org

7.
Chloroplasts…..
• Girdle shaped (Ulothrix)
Image:http://www1.biologie.uni-hamburg.de

8.
Chloroplasts…..
• Stellate (Zygnema)
Image:http://www1.biologie.uni-hamburg.de

9.
Chloroplasts…..
• Reticulate (Chladophora)
Image:https://www.slideserve.com

10.
Chloroplasts…..
• In higher plants – spherical, ovoid, discoidal
or biconvex.

11.
Chloroplasts…..
In higher plants ……
Image: Kristian Peters/CC3.0
https://upload.wikimedia.org

12.
Chloroplasts…..
• In higher plants ……
Image:https://edu.glogster.com

13.
Chloroplasts…..
• In higher plants …..
photographed by Kristian Peters
https://simple.wikipedia.org

14.
Chloroplasts…..
• In higher plants …..

15.
Chloroplasts…..
• In higher plants …..

16.
Chloroplasts…..
Size :
• Average diameter in higher plants – 4 to 6 µm
• Larger in polyploid cells than in diploids
• Chloroplasts of shade plants are larger than
those plants grown in sunlight.
Number :
• Relatively constant in different plants
• Algae often possess a single , large chloroplast
• In higher plants, there are 20 to 40 chloroplasts
per cell.

17.
Chloroplasts - Ultrastructure

18.
Chloroplasts-Ultrastructure Thylakoid (TEM)

19.
Chloroplasts -Ultrastructure….
Image:https://www.burrosabio.net

20.
Ultrastructure of Chloroplast :
• Bounded by two unit membranes of
trilaminar composition.
• The membranes are separated by a space –
periplastidal space.
• Inner contents are heterogeneous

21.
Matrix or Stroma :
• Fills most of the volume of Chloroplast
• A kind of gel – fluid phase
• Contains 50% of chlorophyll proteins , lipids,
DNA (hence, called semi-autonomous
organelle), 70S ribosomes (Plastidoribosomes),
RNA, Fe, Mn, Mg etc.
• Site of CO2 fixation (Dark reaction of
Photosynthesis) and contains all the enzymes
necessary for it .

22.
Thylakoids :
• Consists of flattened vesicles arranged as a
membranous network.
• The outer surface is in contact with the
stroma and its inner surface encloses an
intrathylakoid space.
• The thylakoids may be stacked like a pile of
coins – grana (Sing. Granum) – The number
of thylakoids per granum may vary from a
few to 50 or more – A chloroplast may have
40 to 60 grana .

23.
• Algae have a few thylakoids that do not form
grana.
• Thylakoids of adjacent grana are
interconnected by branching, membraneous
tubules – stroma lamellae (Intergranum
lamellae or Frets).
• The thylakoid membrane contains minute
particles – Quantasomes – photosynthetic unit
– 250 molecules of chlorophyll , the minimum
amount found necessary for photosynthesis.

24.
Functions of Chloroplasts:
1.Photosynthesis : Most important function .
Hence Chloroplasts are also referred to as
‘Photosynthetic apparatus’.
2. Oxygen supply : Provide Oxygen as a byproduct
of photosynthesis.
3. Starch storage : Temporarily store starch grains
during the day time (in the pyrenoid – in
chloroplasts of Algae).
4. Utilize CO2 : They fix CO2 during photosynthesis
thereby keeping its concentration in the air
normal.
5. Change into chromoplasts - in flowers and fruits
to attract animals.

25.
ii) Chromoplasts
• Coloured plastids containing carotenoids and
other pigments – impart colour – yellow,
orange, red etc. to flowers, fruits etc.
• Vary in shape – round , ellipsoidal etc.
• Chloroplasts transform into chromoplasts
during ripening of fruits.

26.
Chromoplasts…..
Each red dot is a chromoplast that contains carotenoids
Image : David Webb, University of Hawaii.
https://www.daviddarling.info

27.
Chromoplasts…..
Image:https://www.qsstudy.com

28.
Chromoplasts…..
Chromoplast - Tim Emeigh
by Timothy
https://www.thinglink.com

29.
Chromoplasts…..
Image:https://gramho.com

30.
Chromoplasts…..
Image:https://sites.google.com

31.
Chromoplasts…..
Chromoplasts in Strelitzia flower
Image:http://biology-assets.anu.edu.au

32.
Chromoplasts…..(from a petal of
Tropaeolum)
Image:https://www.inds.co.uk

33.
Images: https://www.meritnation.com

34.
iii) Leucoplasts
• Colourless plastids found in cells of plant
tissues that are not exposed to light.
• Store carbohydrates , proteins and lipids.
Types :
a) Amyloplasts : The leucoplasts storing starch
– tissues of Potato tuber
b) Proteinoplasts : Leucoplasts storing
proteins- occur in seeds
c) Elaioplasts : Leucoplasts storing lipids (fats
and oils) – found in seeds.

35.
Leucoplasts…..
Amyloplasts

36.
Proteinoplasts

37.
Elaioplasts
plantbiology,siu.edu
http://biogeonerd.blogspot.com

38.
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