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SEED DEVELOPMENT

Seed Formation

Begins at fertilization

Self-pollination – pollen fertilize the ovule from the

same flower (usually flower opens after fertilization)

Cross-pollination – pollen from one flower fertilize a

different flower from the same or a different plant

Seed Formation

True Seeds – is a mature ovule containing embryo,

stored nutrients and seed coat or testa

Diaspores – units of dissemination of plants

resembling seeds (one-seeded, indehiscent fruits

such as achene of Asteraceae, caryopsis of Poaceae,

mericarp of Apiaceae, etc.)

KINGDOM PLANTAE

• Gymnosperms

Seed plants with simple leaves, ovules and seeds exposed

• Angiosperms

Flowering plants, ovules are enclosed in carpel and seeds are

within fruits

• Class Monocotyledones or Liliopsida – monocots- Seeds

with one cotyledon

• Class Dicotyledones or Magnoliopsida – dicots - Seeds

with two cotyledon

See

d

pla

nts

Seed development: embryogeny

• Angiosperms

• True endosperm cells are triploid (3n)

• Two types of endosperm: nuclear (w/ free

nuclear division) or cellular (no free

nuclear division)

Seed development: embryogeny

• Angiosperm

• Monocotyledon

• Dicotyledon

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Seed development: embryogeny

• Angiosperms

• Monocotyledonous

Mature embryo axis seems laterally

attached to scutellum by the scutellar node

Root and root cap enclosed in the

coleorhiza

Epicotyl with several foliar primordia

protected by the coleoptile

Early development of corn

• Five DAP

Embryo is club shaped; upper part becomes

the embryo and lower part to the suspensor

Endosperm has large vacuolated cells

• Ten DAP

Embryo is elongated on one side because of

scutellum growth

Opposite to scutellum is the developing

epicotyl and coleoptile

Early development of corn

• Fifteen DAP

Coleoptile develops further

Leaf primordia are initiated

Epicotyl reoriented to vertical direction

Scutellum enlarges and grows

Radicle and root cap are organized above the

suspensor

• Late embryogenesis

Embryogenesis in rice. A: a fertilized egg (zygote) at 0 DAP; a zygote after first cell division (0 DAP); C:

multicellular zygote at the proembryo stage (2 DAP); D: at the early coleoptile stage; F: at the 1st leaf stage

(5-6 DAP); G: at the 2nd leaf stage (7 DAP); H: mature embryo.

T: terminal cell; B: basal cell; CP: coleoptile; DAP: days after pollination; Sm: shoot meristem; Su: suspensor; Sc:

scutellum; 1st, 2nd, 3rd (leaf); Rd: radicle; Rm: root meristem; CR: coleorhiza; En: endosperm. From: Black, M.,

J.D. Bewley and P. Halmer. Ed. 2006. The encyclopedia of seeds. CABI, Cambridge, MA.

Seed development: embryogeny

• Angiosperms

• Dicotyledonous

Embryos of mature seeds posses two

cotyledons

Storage of reserve nutrients is stored

in the embryo, primarily the cotyledons

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Early development of pea

• Soon after fertilization

Growth of the zygote

Increase in endosperm associated with the

growth of the embryo sac

After the endosperm reaches maximum

volume, embryo grows fast

Early development of pea

• Half seed development

The embryo has the final number of cells

• Late embryogenesis

Embryo cells enlarge at the expense of the

endosperm

Embryo completely fills the embryo sac

From: Esau, K. 1977. Anatomy of seed plants, 2nd ed. John Wiley & Sons.

From: Poehlman, J.M. 1987. Breeding field crops, 3rd ed. Van Nostram Reinhold Publisher

(Scutellum)

coleorhiza

Coleoptile

Seminal root

OVARY FRUIT

OVULE SEED (SOMETIMES FUSES WITH THE FRUIT)

INTEGUMENTS (maternal tissue) TESTA OR SEED COAT

NUCELLUS PERISPERM (USUALLY ABSENT OR REDUCED)

2 POLAR NUCLEI + SPERM

NUCLEUS

ENDOSPERM (TRIPLOID = 3N)

EGG + SPERM NUCLEUS EMBRYO (DIPLOID = 2N)

MYCROPYLE MYCROPYLE

FUNICULUS HILUM (SCAR LEFT BY FUNICULUS)

Seed develops form a

fertilized ovule

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SEED STRUCTURE

Monocotsn

One cotyledon

Oats – Avena sativa

Smooth brome

Bromus inermis

Orchardgrass

Dactylis glomerata

Floret

Canada wildrye

Elymus canadiensis

Spikelet

Rice – Oryza sativa

Spikelet

Barley

Hordeum vulgaris

Big bluestem

Andropogon spp.

glumes

floret

rachilla

central

axis

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Oats – Avena sativa

Popcorn

Sweet corn

White corn

Yellow corn

Zea mays

Rye – Secale cereale

Wheat

Triticum aestivum

cotyledon

radicle

hypocotyl

testa

Onion Allium cepa

perisperm

Dicots

Two cotyledons

Three types of ovules

A. Orthotropous – in line

B. Anatropous – 180° curvature (most common)

C. Campylotropous – curved embryo sac

Bean

Phaseolus spp.

Soybeans Glycine max

Cowpea, black-eyed pea

Vigna unguiculata

subsp. unguiculata

micropile

strophiole

hilum

clef

Garden bean

Phaseolus vulgaris

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Sunflower: achene

Pericarp

Seed coat

Cotyledon

Drawing showing a mature seed of Capsicum annum (pepper) (Color image by Katrin

Hermann based on a EM image by Watkins and Cantliffe, Plant Physiol 72: 146-150, 1983).

http://www.seedbiology.de/structure.asp#pepper1

Endospermic dicots: tomato and pepper

Seeds developed from Anatropous

ovules usually have raphe

raphe

caruncle

Castor bean Ricinus communis

Outgrowth of outer integuments

Endospermic dicots: castor beans

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Structure of mature fruits and seeds of Beta vulgaris.

Hermann K et al. J. Exp. Bot. 2007;58:3047-3060

© 2007 The Author(s).

chalazal cap

or operculum

raphe

Cotton Gossipium hirsutum

Peanut Arachis hipogaea

raphe

point of

attachment

Cotyledons (8)

Female gametophyte

testa

Pine Pinus spp.

radicle wing

References:

Copeland, L. O. & M. B. McDonald. Principles of Seed

Science and Technology, 3rd ed.

Esau, K. 1977. Anatomy of Seed Plants, 2nd ed. John

Wiley & Sons.

SCST Seed Technologist Training Manual.

Some photos used in these slides were obtained from a

collection by Mississippi State University Seed Technology

Laboratory