3. INTRODUCTION
Endosperm is a nutritive tissue stored in the seed for the embryo and it is
formed by the fusion of one male gamete with the polar nuclei.
Endosperm plays a main role in the diet of human beings.
Endosperm is found in all angiosperms except few families like Orchidaceae,
Podostemonaceae and Trapaceae.
The seeds without endosperm: Nonendospermous seeds or exalbuminous
seed.
The seed containing the endosperm: Endospermous or albuminous seed.
Endosperm is replaced by fleshy cotyledons in dicotyledons.
In monocotyledons, endosperm persists in the mature seeds too and stores the
food.
Endosperm tissue is rich in carbohydrates and also contains proteins and
lipids.
4. Salient features of Endosperm
• Endosperm development takes place from the triploid cell (3n) in the
embryo sac.
• The second male gamete fuses with the diploid secondary nucleus (formed by
2 polar nuclei) to form primary endosperm nucleus (PEN) and a triploid cell.
The process is known as triple fusion
• Endospermic cells are mostly triploid but in some plants, they may be
diploid (water lily) or polyploid (up to 15n)
• In some of the dicots, mature seeds contain food stored in the endosperm,
they are called endospermic or albuminous seeds, e.g. castor
• In beans, peas, gram seeds, the endosperm is completely absorbed during
development and food is stored in two cotyledons. They are called
exalbuminous seeds
• Endosperm mostly contains starch as a food reserve, but it may contain
fats, e.g. castor
5. • Endosperm provide nutrients to seeds during dormancy
• Endosperm also contains certain hormones like cytokinins and helps in cell
differentiation
• In grains, like wheat, maize, barley, corn, the endosperm is the main
source of food
• The white flour, used to prepare bread, only contains endosperm of wheat
seeds
• The outer layer of endosperm is the aleurone layer. It secretes the amylase
enzyme, which breaks down the starch contained in the endosperm to
sugars for utilisation by seedlings
• Orchid seeds lack an endosperm
Coconut water is the
example of a liquid
endosperm
6. Types of Endosperm
How the primary endosperm nucleus (PEN) develops into
endosperm differs in various plants. Endosperms are divided into
three main types based on their development pattern.
1. Nuclear Endosperm
2. Cellular Endosperm
3.Helobial Endosperm
Of these three types,
• nuclear endosperm is the most common and is found in about 56% families of
angiosperms.
• Cellular endosperms occurs in 25% families.
• Helobial endosperm occurs in 19% families.
• Furthure , cellular endosperm is mostly confined to dicotyledonous families and
helobial endosperm to the monocotyledonous families.
• Where the embryos grows slowly and seed contain immature undifferentiated
embryo , the endosperm is cellular.
9. 1. Nuclear Endosperm:
In this type of endosperm, the division of the primary endosperm
nucleus and its further divisions are not followed by wall formation.
• It is the most common type of endosperm found.
• Here PEN divides repeatedly (mitotic division) without cytokinesis. It results
in the formation of a large number of free nuclei in the cell.
• A large central vacuole is formed and nuclei get arranged at the
periphery. There are more nuclei at the chalazal and micropylar end,
compared to the sides.
• At this stage, cell wall formation takes place from the periphery towards the
centre and multicellular endosperm is formed.
Examples: maize, rice, wheat, cotton, sunflower, Limnanthes,
Oxyspora
10. Figure: Stages in the development of nuclear type of endosperm.
1. Nuclear Endosperm:
11. In Lomatia, besides the main chalazal haustorium, numerous
single- celled, fingershaped projections are present all over the
endosperm. This increases the absorbing surface of the
endosperm.
1. Nuclear Endosperm:
12. 1. Nuclear Endosperm:
In Grevillea robusta, presence of vermiform appendage at the chalazal
end of the endosperm is reported, in which, chalazal endosperm haustorium
remains free- nuclear.
13. • In Crotalaria, the wall formation is
confined to the upper region of the
embryo sac, the chalazal region
remains free- nuclear, and it often
elongates and behaves like an
haustorium.
1. Nuclear Endosperm:
14. In Coconut, the cell wall formation is incomplete resulting
in the outer multicellular solid endosperm and inner
multinucleated (having free nuclei) liquid endosperm (coconut
milk)
1. Nuclear Endosperm:
16. 2. Cellular Endosperm:
It is not very common.
In this type of development, division of PEN (karyokinesis) is followed by
cytokinesis and two cells are formed due to transverse division, giving rise
to the chalazal and micropylar chamber. Further division is similar, which
leads to the formation of the cellular endosperm.
Examples: Petunia, Balsam, Datura
The cellular endosperm is characterized by the absence of free nuclear
stage.
The division of the primary endosperm nucleus and a few subsequent
nuclear divisions are followed regularly by wall formation.
The occurrence of haustoria is a common feature of this type of
endosperm;
It is more varied than that is the nuclear endosperm.
The haustoria may be micropylar or chalazal and occasionally, present in the
same plant.
17. A very aggressive chalazal haustorium is formed in Iodina rhombifolia.
The haustorium is actually formed before fertilization.
After fertilization, the division of the primary endosperm nucleus is followed
by transverse partitioning of the central cell, resulting in the formation of a
micropylar chamber and a chalazal chamber.
The endosperm proper is derived from the micropylar chamber alone. The
chalazal chamber functions as an aggressive, uninucleate haustorium.
Profuse branching at the free- end gives the haustorium a coralloid
appearance.
In the Acanthaceae, the endosperm development is asymmetric and
it shows characteristic micropylar and chalazal haustoria.
2. Cellular Endosperm:
20. 3. Helobial Endosperm:
• Development of helobial endospermis intermediate between nuclear and
cellulartypes.
• The first division is similar to cellular endosperm and results in a large
micropylar cell and small chalazal cell. The chalazal cell mostly does not
divide further and functions as a base cell. The micropylar cell divides
further, similar to nuclear endosperm. So it is an intermediate type, a
combination of both nuclear and cellular endosperm.
• Examples: Eremurus
• Helobial endosperm is more common in monocot.
23. Function of Endosperm
• Endosperm is important for the growth of an embryo and
stores the food reserve
• They supply nutrients and provide protection to the
developing embryo
• Endospermic tissues have shown to regulate gene expression
and seed germination
• Endosperm induces signals according to environmental
conditions and regulates embryonic growth
• The endosperm contains cytokinin, which regulates cellular
differentiation
• It may induce abortion of seeds from the genetically
mismatched cross
24. ENDOSPERM HOSTORIA
1. MACADAMIA TERNIFOLIA :
The lower free nuclear part forms many lobes or projections. Which
invade the nutritive tissue at the chalazal end Of the ovule and functions as
haustoria
25. Vermiform appendage.
2.GRAVILLEA ROBUSTA : In Gravillea robusta , the
lower coenocytic Part of the endosperm is very
aggressive & grows in the form of spiral, tubular
worm like apendage. Hence it called Vermiform
appendage. In this type the cells of the chalazal
region of the ovule practically get dissolved due to
the activity of the haustoria ( Aggressive
haustoria).
In later stages, the vermiform appendages
gets partitioned into many large chambers. The
cells formed in this way may be said to be
secondary endosperm tissue.
26. Cucumis sativus
• In cucumis ( cucurbitacae) a long chalazal haustorium is
present. Soon after the fertilization, the lower part of the
embrysac grows downward into a long tubular structure.
• When the embryo is at the globular stage, the upper part of the
endosperm becomes cellular and is designated as the
endosperm proper.
• The lower free nuclear part the endosperm further elongates
and reaches deep down in the chalazal region.
• The chalazal haustorium consists of dense cytoplasm and
varied size of nuclei.
• Sometimes the tip of the haustorium becomes swollen.
• This haustorium transport the nutrients to the developing
embryo.
27. Ruminate endosperm
• It shows fringed outline or irregularly crinkled margin, bearing
such type of endosperm is called Ruminate endosperm.
• This is not a 4rth type of endosperm. Any one of the endosperm (
cellular, nuclear, helobial)may become ruminate endosperm.
• This type of endosperm is found in 32 angiosperm familes.
• In 1962 periasamy worked extensively on Ruminate endosperm.
• Rumination of the endosperm is caused by the activity of the seed
coat or by the endosperm itself.
28. • Rumination may be divided into 2 types
1. The inner layer of the seed coat are uneven and leave a
number of gaps in the interior region. The surface of the
endosperm growing rapidly and fills all this cavities and
form the ruminate endosperm
• Eg: Andrographis
2. In cocoloba, the rapid growth of the endosperm utilize the
ephemeral nucleus and digests during the early stage of
seed development. As a result of this the inner seed coat
becomes uneven and affecting the surface of endosperm
making it Ruminate.
