3. INTRODUCTION
Plastids are large cytoplasmic organelles.
Plastids are major organelles found in the cells of plants and algae.
Plastids are the site of manufacture and storage of important
chemical compounds used by the cell.
Plastids often contain pigments used in photosynthesis and the
types of pigments used in photosynthesis and the types of pigments
present can change or determine the cell’s colour.
4. The term plastids was derived from the Greek word plastikas
meaning formed or moulded.
This term was coined by schimper in 1885.
In plants, plastids may differentiate into several forms,
depending upon which function they need to play in the cell.
The plastids are broadly classified into two main types namely
chromoplasts and leucoplasts.
6. CHROMOPLAST
Chroma (Colour) + Plast (Living).
They may be round or needle shaped ellipsoidal.
These are colour plastids containing carotenoids, Xanthophyl and other
pigments.
It’s found in flower petals, fruit, some roots.
Flower are coloured by chromoplast and insects attract towards flower
for pollination and dispersal.
There is reduce chlorophyll in chromoplast.
7. For Red colour Pigmentation – Charotein family Lycopene
For Yellow colour - Xanthophyll
For Brown colour – Fucoxanthene
In bacteria various pigments like phycocyamin, chlorophyll,
carotenoid, erythrin etc are present.
They are following types:
(1) Phaeoplast : Phaeo- Dark or Brown.
Pigment – Fucoxanthene.
Found in diatoms.
(2) Rhodoplast :
Pigment – Phaeoerythrin.
Found in red algal.
8. LEUCOPLAST
Leuco (White) + Plast (Living).
They are colorless.
They are found in embryonic and germ cells and meristematic
cell.
Leucoplasts don’t have thylakoid and ribosome.
They store the food materials.
9. TYPES OF LEUCOPLAST
PROTEINOPLAST : It stores protein as aleurone molecule.
So it’s also called as Aleuronoplast.
Eg – Riccicus comunis.
AMYLOPLAST : They store starch.
Eg – Potato, Rice.
ELAIOPLASTS : They store Lipid. It’s found seeds of
monocotyledons and dicotyledons.
10. CHLOROPLAST
Discovered – Schimper
Chlor (green) + plast (living)
It’s present mostly in the green algae and higher plants.
In higher plants the chloroplasts are generally lens shaped, about 2-
4µm wide and 5-10µm long.
Number of chloroplasts from 20 to 40 per cell in higher plant.
This is double membranous organelles.
This is the most active photosynthetic tissue.
12. Proteinaceous ground substance present in it ῶ is called stroma.
70s Ribosome, granum, thylakoid, oxyphilic drops, starch, protein etc
are found in stroma.
Circular DNA is present which is called plastidom.
In presence of DNA, RNA It’s called cell of cell or Semi-Autonomous
organ.
In chloroplast, Chlorophyll a and b RNA are found.
In general chloroplasts have a double helical DNA circular with an
average length of 45mm (about 1,35,000 base pair).
13. FUNCTION OF CHLOROPLAST
Photosynthesis : Photosynthesis occurs inside the chloroplast.
Thses are considered as the centers of photosynthetic.
Protein Synthesis : They have sufficient amount of mRNA of its
own. So chloroplast activity incorporate amino acid into protein,
in the presence of CO2.
Calvin cycle occurs in it/in stroma.
14. Mutation : This is known as plastid mutation. After mutation
plastid may perform altered functions.
Cytoplasmic Heredity : It occurs in present of DNA.
Role in Krebs Cycle and Fatty Acid Synthesis : It provides
enzymes.
Light reaction occurs in granum.
