Membrane-bound cell organelles found in plant cells, algae and some of the eukaryotic cells, Plastids play a very important role in cells.
For plants, they are extremely important because they play a role in photosynthesis. We guess you already know why photosynthesis is important.
Right! Without photosynthesis, plants will die and so will the herbivores, followed by carnivores and omnivores.
In this article on plastid facts you will get a good idea of what they are and what they do in plant cells.
Ready to learn?
Plastids Facts: 1-4 | What are they and where are they found?
1. Plastids are nearly spherical or disc-shaped cell organelles (around 1 μm to 1 millimeter in diameter) floating freely in cytoplasm.
2. However, they can be found as elongated, lobed or even show amoeboid features.
4. Plastids are absent in bacteria, animals, fungi, sperm cells of plants.
Plastids Facts: 5-10 | Structure and contents of plastids
5. Plastids have double bounding membrane, spherical lipid droplets called plastoglobuli, and framework of internal membrane of various internal vesicles.
7. The number of plastids usually vary from species to species but on an average the numbers are between 30 -40 and 100-150 in cells which are diploid.
8. It may surprise you but the plastids of plants are simpler than the plastids of algae!
9. Plastids are interconnected with each other via stromules (stroma-filled tubules). Stromules connect the plastids and form a network called plasidome. Stromules also connect plastids with other cell organelles.
10. Plastids (as they contain DNA) are self-replicating cell organelles just like mitochondria.
Plastids Facts: 11 | Function
11. Plastids perform an extremely important function – synthesis of food and storage of lipids, proteins and carbohydrates.
Plastids Facts: 12-14 | Formation of Plastids
12. The plastids originate from proplastids which are undifferentiated cell organelles. They are small having a diameter of around 0.5 to 1 µm.
13. These proplastids then develop into mature plastids which get differentiated.
14. The development of plastids is controlled by internal program of the differentiation of cells. Environmental conditions also have a say in the development of plastids.
Plastids Facts: 15-17 | Name and discovery
15. The term “plastid” is derived from “plastikas” which is a Greek word. Plastikas meant molded or formed.
16. Ernst Haeckel was the person to discover them and to use the term plastid.
17. However, a clear definition was given by A. F. W. Schimper in the year 1885.
Plastids Facts: 18 | Types of plastids
18. Andreas Franz Wilhelm Schimper classified plastids into the four types which are as follows:
Plastids Facts: 19-42 | Leucoplasts and their types
19. The term leucoplast is a combination of two Greek words “leuco” meaning white and “plast” meaning living.
20. As the name suggests, leucoplasts are the colorless plastids.
21. They are found in germ cells, embryonic cells, meristematic cells and in all the cells where the plant doesn’t receive sunlight.
22. For some time, cotyledons (embryonic leaf in plants which bear seeds) and primordium of stems (structure of stem present in earliest stage of the development) remain colorless.
23. But both the cotyledons and primordium become green because the plastids (which were leucoplasts) get filled with chlorophyll and become chloroplasts.
24. Epidermal cells and internal plant tissues are generally considered as true leucoplasts because they never become green or photosynthesize.
25. They don’t contain ribosomes and they store food in the form of proteins, carbohydrates, and lipids.
Plastids Facts: Types of Leucoplasts
26. Leucoplasts are of four different types. They are:
27. The term amyloplast is derived from two words – “Amyl” and “Plast.” Amyl is a Latin word which means “starch”. Plast is a Greek word which means “living.”
28. In some plant tissues like potato, amyloplasts can grow to the size of a normal animal cell.
29. The outer membrane of amyloplasts contains one to eight starch granules.
30. Starch granules are nothing but concentric layers of starch and sometimes they may become so large that the encasing membrane ruptures.
31. It is also suggested that amyloplasts help in gravimetric sensors i.e. the amyloplasts help in directing the growth of root in the ground.
32. They also help in producing some enzymes in some species.
33. Elaioplasts are also known as Lipoplasts.
34. The word elaioplast is derived from two Greek words “elaiov” meaning olive and “plast” meaning living.
35. Elaioplasts don’t have any particular internal structure. They are small and spherical shape.
36. They are rare and few compared to other plastids.
37. They store lipids and oil droplets called plastoglobuli.
38. They are present in monocotyledon seeds and in dicotyledons. They are also present in tapetum (a layer which have nutritive cells present within anther) in some plants.
39. In these plants, they help in the maturation of pollen wall.
40. Proteinoplasts store proteins and they are present in seeds and some of the thylakoids (Membrane bounded flattened sacs present inside the chloroplasts).
41. They are large and the proteins are stored in amorphous or in crystalline form.
42. They synthesize and store tannins and polyphenols.
Plastids Facts: 43-62 | Chromoplasts and their types
43. The word chromoplast is derived from two Greek words “chroma” meaning color and “plast” meaning living.
44. Chromoplasts are the colored counterparts of leucoplasts.
45. Chromoplasts contain carotenoids and other pigments.
47. The structure of chromoplasts is diverse, they can be needle-shaped, spherical, ellipsoidal, etc.
48. The pigments present in the chromoplasts are either in droplets or are in crystalline form.
49. The function of chromoplasts is exactly not known.
50. However, it is believed that the colors that chromoplasts impart especially in fruits and flowers help in attracting the insects or other animals thereby helping in pollination and seed dispersal.
51. Chromoplasts have very less amount of chlorophyll which is not at all present in leucoplasts.
52. As chlorophyll content is low, chromoplasts rank lower in photosynthetic activity too.
53. Carrots contain alpha carotenoids and beta carotenoids; tomatoes have lycopene, both being the members of carotenoid family.
54. Cyanobacteria or blue green alga contain phycoerythrin, phycocyanin along with carotenoids, chloroplasts etc.
55. Did you know that chromoplasts can be formed from chloroplasts? This is how mangoes or any fleshy fruits changes its color from green (because of chloroplasts) to yellow, orange, red etc. once they ripen.
Plastids Facts: Types of Chromoplasts
56. Chromoplasts are divided into two types:
57. The word phaeoplast is derived from two Greek words – “phase” meaning ‘dark or brown’ and “plast” meaning ‘living.’
58. Phaeoplast contains fucoxanthin which absorbs sunlight.
59. They are seen in diatoms, dinoflagellates and even brown alga.
60. Just like phaeoplast, rhodoplast is also derived by combining two Greek words “rhode” (meaning red) and “plast” (meaning living).
61. Rhodoplasts contain phaeoerythrin pigment which helps in absorbing sunlight.
62. Rhodoplasts are seen in red algae.
Plastids Facts: 63-70 | Chloroplasts
63. Two Greek words chlor (meaning green) and plast (meaning living) are combined to form the word chloroplast.
64. Chloroplasts are the most abundant plastids in plants.
65. Chloroplast is present mostly in higher plants and green algae.
66. It contains chlorophyll a and chlorophyll b pigments.
67. Chloroplast also contains DNA and RNA.
68. There is something called etioplasts. Etioplasts are considered to be an inadequate laboratory model of the development of chloroplasts from the proplastids.
69. Etioplasts are formed in the tissues which stay unexposed to sunlight. They appear mostly in young tissues where the photosynthetic apparatus has not been differentiated properly.
70. Etioplasts stage is considered as the intermediate stage.
Plastids Facts: 71-75 | Gerontoplasts
71. These plastids are formed during the senescene i.e., gerontoplasts are formed when the cells are aging and are about to die.
72. The gerontoplasts are formed from chloroplasts.
73. Chloroplasts undergoes a lot of structural changes to transform itself into gerontoplasts.
74. It is a controlled degradation of chloroplasts where the chloroplasts succeed in saving around 75% of the total leaf protein.
75. The chloroplasts remove the pigments as well which have the potential to become toxic to the cell.
Did you know? According to Schimper, plastids can transform into one another easily!
Sources: 1. Cell Biology by P.S. Verma and V.K. Agarwal Chapter 17th Chloroplasts, Pg. No. 374 to 376. 2. plantcellbiology.masters.grkraj.org 3. microscopemaster.com 4. link.springer.com 5. ncbi.nlm.nih.gov 6. Wikipedia