BYMEDIDA SUNIL KUMAR

PH. D FIRST YEAR

DEPT. OF AGORONOMY

Embryo and Endosperm development

LEC: 3

Female gametophyte development

Male gametophyte development

Angiosperm Double Fertilization

Abbreviations: T, Terminal cell; B, Basal cell; EP, Embryo Proper; S, Suspensor; Bc,

Suspensor Basal Cell; Pd, Protoderm; u, Upper Tier; I, Lower Tier; Hs, Hypophysis; Pc,

Procambium; Gm, Ground Meristem; C, Cotyledon; A, Axis; MPE, Micropylar end; CE,

Chalazal End; SC, Seed Coat; En, Endosperm; SM, Shoot Meristem; & RM, Root Meristem.

Overview of plant embryogenesis

Types of embryogeny

Based on the type of divisions pro-embryos are classified as

• Crucifer

• Asterad

• Solanad

• Caryophyllad

• Chenopodiad

• Piperad

PolyembryonyPolyembryony is the phenomenon of two or more embryos developing from a

single fertilized egg

Types of Polyembryony:

1. Simple Polyembryony:

More than one egg cells get fertilized. Eg: Brassica

2. Mixed Polyembryony:

When more than one pollen tube enters into an embryo sac and extra-

male gametes fuse with synnergids or antipodal cells. Eg: Allium

3. Adventives Polyembryony:

Sometimes, the diploid nucellar or integumentary cells may develop

additional embryos. Eg: Citrus

4. Cleavage Polyembryony:

Occurs due to cleavage of the embryos as in the case of the Orchids

Endosperm development• Endosperm is the nutritive tissue formed as a result of triple fusion

in the angiosperms.

• Endosperm formation starts prior to embryo formation.

• Reaches its maximum morphological development at

physiological maturity

Based on the mode of development of endosperms:

Nuclear

Cellular

Helobial

Nuclear endosperm

Primary endosperm nucleus divides repeatedly to form a large number of free nuclei.

No cell plate formation takes place at this stage and a central vacuole appears later.

It is followed by cell plate formation which is centripetal.

It is the most common type of endosperm e.g., Cotton, Maize, Capsella, Coconut

(milk), wheat, etc .

Cellular endosperm

Cell wall formation occurs immediately after division

Subsequent divisions also accompanied by cell plate formation.

As a result, the endosperm becomes cellular from the beginning.

Eg: - Balsam, Petunia, barley, grasses, Petunia, Utricularia, Coconut (copra).

Helobial endosperm

Intermediate above two type e.g., members of order helobiales (Monocot)

First division is cellular (i.e., wall formation follows the first division)

However, inside each of these newly formed cells, free nuclear divisions occur.

But finally, the endosperm becomes cellular following the pattern of

development of nuclear endosperms.

Perisperm

• The nucellus is the central portion of the ovule inside the integuments.

• After fertilization, the nucellus may develop into the perisperm that feeds

the embryo.

• An integument is a protective cell layer surrounding the ovule.

• Gymnosperms typically have one integument (unitegmic) while

angiosperms typically have two (bitegmic).

• The inner integument has been proposed to have formed from sterile

branches surrounding a terminal mega sporangium.

• The integuments develop into the seed coat when the ovule matures after

fertilization.

Seed coat• Primine Testa (external)

• Secundine Tegma (inner)

Functions of seed coat:

• Protection against action of biotic and abiotic factors

• Regulation of water and gaseous exchange

• Regulation of germination and dormancy mechanisms

• Control of seed dispersion: wings, hairs, mucilages, etc

• The integuments do not enclose the nucellus completely but leave an opening at

its apex referred to as the micropyle.

• The micropyle opening allows pollen to enter the ovule for fertilization.

• Located opposite from the micropyle is the Chalaza where the nucellus is joined

to the integuments.

• Nutrients from the plant travel through the phloem of the vascular system to the

funiculus and outer integument and from there apoplastically and symplatically

through the chalaza to the nucellus inside the ovule.

• In chalazogamous plants, the pollen tubes enter the ovule through the chalaza

instead of the micropyle opening.

Stages of seed development

• Histo differentiation: -

Cell division

• Seed expansion (maturation): -

Genes for synthesis of reserves are expressed, deposition of

reserves.

• Maturation (drying) / desiccation: -

Water loss, embryo becomes quiescent state (metabolically

inactive).

Key Processes During Seed Maturation

Accumulation of food reserves

Hardening of seed coat & accumulation of antimicrobial compounds

Mechanisms of seed dispersal – flyers

Synthesis of protective compounds that allow the seed to withstand some

degree of water loss and adverse environmental conditions.

Eg. antioxidants, antimicrobial, resistance to pathogens.

Dormancy: - can happen for many years, needs signals or conditions to

break the dormancy (eg. conifers at moist and low temperatures) or

smoke

Longitudinal sections through ripe seeds

Phases in Seed Development

• Phase I – Cell Division

• Phase II – Expansion of the cell

• Phase III – Accumulation of Dry mass

• Phase IV – Seed Moisture loss

ENVIRONMENTAL EFFECTS ON SEED DEVELOPMENT

Environmental factors effecting Seed Development

Decline in seed number

Seed weight

Physiological potentiality

Degree of damage depends on

Stage of stress occurrence

Type of stress

Intensity of stress

Duration of stress

Components of Environment

Soil Fertility

Water

Temperature

Light

Seed position on the plant