Steps in seed germination

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BIOCHEMISTRY OF SEED GERMINATION
Prepared by
Dr. K. Vanangamudi
Formerly Dean (Agriculture), AC & RI, Coimbatore,
Dean, Adhiparashakthi Agricultural College, Kalavai,
Professor and Head - Seed Science and Technology,
Tamil Nadu Agricultural University, Coimbatore.

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BIOCHEMISTRY OF
GERMINATION

3. GERMINATION EVENTS
Stages EVENTS
Pre-
germination
(a) Rehydration – imbibition of water.
(b) RNA & protein synthesis stimulated.
(c) Increased metabolism – increased respiration.
(d) Hydrolysis (digestion) of food reserves by
enzymes.
(e) Changes in cell ultrastructure.
Germination (a) Rupture of seed coat.
(b) Emergence of seedling, usually radicle first.
Post -
germination
(a) Induction of cell division & cell growth.
(b) Controlled growth of root and shoot axis.
(c) Controlled transport of materials from food
stores to growing axis.
(d) Senescence (aging) of food storage tissues.
1/12/2023 3

4. WATER UPTAKE BY A SEED
Triphasic
Phase I : A rapid initial uptake (imbibition)
Phase II : A plateau phase (metabolic preparation
for germination)
Phase III : Further increase in water uptake
which occurs directly after germination is
completed.
Phase III water uptake causes hydraulic growth
of the embryo and the emerged seedling.
ABA inhibits phase III water uptake

5. Seed germination

6. 2 The aleurone responds
by synthesizing and
secreting
digestive enzymes that
hydrolyze stored nutrients
in the endosperm. One
example
is -amylase, which
hydrolyzes
starch.
Aleurone
Endosperm
Water
Scutellum
(cotyledon)
GA
GA
-amylase
Radicle
Sugar
1 After a seed
imbibes water, the
embryo releases
gibberellin (GA)
as a signal to the
aleurone, the thin
outer layer of the
endosperm.
3 Sugars and other
nutrients absorbed
from the endosperm
by the scutellum
(cotyledon) are
consumed during
growth of the embryo
into a seedling.

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8. ENZYME ACTIVATION- Stages leading to cell division
Mitchondria
reconstituted Soluble sugars
Respiration
Initially anaerobic
Later aerobic
ATP
RNA activated
Polysomes
Protein synthesis (0.5h)
Enzymes (proteins)
Mitosis (70h)
DNA synthesis (45h)

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