The document discusses endosperm, a vital plant tissue in fertilized seeds that provides nutrients to developing embryos and seedlings. It outlines various types of endosperm development, including nuclear, cellular, and helobial types, along with specific characteristics and examples. Additionally, it highlights functions, variations, and unique cases like ruminate and mosaic endosperm in different plant families.

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ENDOSPERM
 Endosperm is an unique and important plant tissue present in the fertilized ovule
(seed)
 It is a highly specialised, nutritive, colourless, polyploidy (usually triploid) sporophytic
tissue derived from the primary endosperm nucleus (PEN) due to the occurrence of
triple fusion.
 Triple fusion is the second fusion of the haploid polar nuclei(n+n) of the central cell
(embryo sac) with the nucleus of the second male gamete (n) resulting a triploid PEN.
 It provides the nutrients primarily for the developing embryo and to the germinating
young seedlings (albuminous seeds).
 The central cell of the embryo sac is the storehouse of Endosperm.
 It is present in almost all angiosperms except in the families 1) Orchidaceae 2)
Podostomaceae & 3)Trapaceae.
 Endosperm is formed due to the occurrence of the normal or asymmetric mitotic
divisions of the PEN.
 Endosperm is a highly varied plant tissue in terms of its nature, structure, composition,
ploidy, nutrients and development.
 It may be of the nuclear, cellular or both in structure.
 Further, it may be coloured (Mosaic), aggregate (composite) and with rough surface
(Ruminate).
 It is usually achlorophyllous, but in Crinum, Raphanus and Viscum it becomes
chlorophyllous (green endosperm).
 The cells of endosperm are usually isodiametric with thick or thin cell walls made up
of mainly hemicellulose.
 They are usually with the large nuclei because of polyploidy level. Mostly cells are
triploid (3N), even up to 9N condition (Peparomia). However, it is diploid in Oenothera.
 It is rich with carbohydrates (Starch), oils and proteins.
 In case of Poaceae, this tissue is with a highly specialised peripheral layer called
Aleurone layer. It is rich with proteins and oil nutrients.
 It also produces a number of vermiform long appendages called haustoria, which
absorb nutrients from the other ovular tissues.

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A) Based on the mode of development, Endosperm may be
1) Nuclear Endosperm
2) Cellular Endosperm, and
3) Helobial Endosperm
B) Based on the nature / texture /colour.
4) Composite Endosperm (Loranthaceae)
5) Ruminate Endosperm (Annonaceae+ 31 families)
6) Mosaic Endosperm (Maize, petunia)
1. Nuclear Endosperm:
 It is a major type of endosperm which occurs in about 60% of angiosperms
 In this type of endosperm, the division of the PEN and a few subsequent nuclear
divisions are not accompanied by the wall formation.
 This results in a condition where the central cell of the embryo sac is filled with a
few hundred to several thousands suspended nuclei in the sap.
 This condition of endosperm maybe persist until it consumed by the developing
embryo (Oxyspora) or it may become cellular at a later stage (Cocos nucifera).
 Cellularization at a later stage is more common and where the wall formation is
mostly centripetal (i.e., from the periphery towards the centre)
 In young coconut (5cm size) the endosperm is filled with free nuclear sap, a
developing (10cm) coconut possess both cellularized and free nuclear liquid,
However, the matured old coconut is with more cellular Endosperm.Presence of
haustoria is less common.

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2. Cellular Endosperm
 This type of endosperm development is more common in dicotyledons.
 In this type of endosperm, the PEN is subject to several normal mitotic divisions,
wherein both the karyokinesis and cytokinesis will occur successively.
 It is categorised by the absence of free nuclear stage
 Presence of haustoria is the common feature of cellular endosperm.
Ex: Grewelia robusta. Cucumis sativa and Crotolaria juncea.
 The haustoria may be more varied structures than in the nuclear endosperm. They
maybe micropylar (Hydrosera triflora) or chalazal (Cucumis) ends, Occasionally
both the types of haustoria are present in the same plant (Melampyrum lineare).

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3. Helobial Endosperm
 It mainly occurs in the monocots (14 families in order to Helobiales) hence called
Helobial endosperm.
 It is an intermediate type between the cellular and nuclear types of endosperm.
 It share the feature of the both types.
 During its development, the PEN moves towards the chalazal end of the embryo
sac, where it divides forming a large micropylar chamber and a small chalazal
chamber
 As a rule, the micropylar chamber nucleus will undergo initially free nuclear
divisions followed by the wall formation at later stage.
 While, the nucleus of the chalazal chamber either remains undivided or divides
only a few times. If it divides, it may be free nuclear or sometimes become
cellular (Phylidrum lanuginasum)

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4. Ruminate Endosperm:
 The mature endosperm with any degree of irregularly and unevenness on its
surface contour is called ruminate endosperm.
 It starts at a later stage of endosperm development.
 It may belongs to the cellular or helobial endosperm.
 It is reported in 32 families including Annonaceae and Aristalochiaceae.
 It is the resultant of due to the activity of seed coat (Annona) or the endosperm
itself (Myristica)
Figure 1 Annona seed with Ruminate Endosperm Figure 2 the variants of Ruminate Endosperm
5. Composite Endosperm
 It is reported in a parasitic dicotyledonous family Loranthaceae
 In this family, ovules are absent in the ovary, However, several long tubular embryo
sacs are developed at the basal portion of the ovary.
 After fertilization, all the embryo sacs produce the cellular endosperm, which fuses
together, and form a composite tissue, hence called composite endosperm.
Figure: showing the fused embryo sacs with composite endosperm

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6. Mosaic Endosperm
 The differential colour of endosperm like mosaic appearance is called Mosaic
Endosperm.
 It is first reported in maize (Webber, 1990), where does it has the alternate
patches of the red and white coloured endosperm.
 It Indicates the differential distribution of starch and sugars
 It is also reported in Petunia and Lycopersicon (Tomato)
Functions of Endosperm:
1. It provide nutrients for the developing embryo (i.e. from zygote to proembryo)
2. Also provides nutrients to the young seedlings (Albuminous seeds).
3. Produces endospermic embryos rarely (Brachiaria setigera).
4. Sometimes behaves as a cambium (in grasses).
Additional Information;
Perisperm: The nucellus present in the seed is called Perisperm. It may also serve as the nutritive
tissue for the developing Embryo especially in the absence of Endosperm
Xenia: The effect of pollen on the endoperm is called Xenia. The mosic endosperm is the
outcome of Xenia in Maize.
Metaxenia: The effect of pollen both on the seed and fruit features is called Metaxenia
Albuminous Seed: These are Endospermic seeds like cereals, millets and oil seeds
Ex-albuminous seed: These are the seeds with non-endospermic or the endosperm
completely used up for the ebryo development
Note: This document is prepared by Dr PB Mallikharjuna, Associate Professor & Head , Govt. First Grade College,
Yelahanka , Bangalore as a part of online class on 27-04-2020
References : 1. Bhojwani & Bhatnagar : Embryology of Angiosperms
2. Dwivedi JN : Embryology of Angiosperms
3. Maheshwari P : Embryology of Angiosperms
4. www.slideshare.com & www.google com /images