This document summarizes a presentation on plant biochemistry focusing on seed dormancy. It defines seed dormancy as when seeds are prevented from germinating under normal conditions. It discusses the different types of seed dormancy including seed-coat induced, embryo-induced, and secondary dormancy. The causes of seed dormancy include hard seed coats, underdeveloped or dormant embryos, and the presence of germination inhibitors. Methods for breaking dormancy include scarification, stratification, and the use of alternating temperatures, light, and growth regulators. Seed dormancy provides advantages like helping plants survive cold temperatures and ensuring survival in tropical regions. Factors that affect germination include water, temperature, atmospheric conditions, soil properties, and seed

1. PRESENTED BY
ANKIT
SUBJECT :- PLANT BIOCHEMISTRY
M.SC SEM. 1ST
DEPARTMENT OF BIO-CHEMISTRY
DR.B.R.A. UNIVERSITY

2. CONTENT
. INTRODUCTION
• TYPES OF SEED DORMANCY
• CAUSES OF THE SEED DORMANCY
• METHODS OF BREAKING SEED DORMANCY
• ADVANTAGES OF SEED DORMANCY
• GERMINATION
• CHANGES IN FOOD RESERVES ETC
• FACTORS AFFECTING GERMINATION
CHOTELAL

3. INTRODUCTION
Seed dormancy is defined as a state in which
seeds are prevented from germinating even under
environmental conditions normally favorable
for germination.

4. TYPES OF SEED DORMANCY
CROCKER (1916) divided seed-dormancy into
seed-coat induced dormancy embryo-induced
dormancy.
• Seed-coat induced dormancy: The dormancy
of seeds due to extreme hardness of seed- coat is
called seed-coat dormancy.
• Embryo induced dormancy : The dormancy
of seeds due to rudimentary or complete
dormant embryo is called embryo induced
dormancy.

5. Other types of dormancy may be.
• Secondary dormancy :
when the seeds become dormant
again after
breaking the dormancy, it is called
secondary dormancy.
• Special type of dormancy : The failure
of seedling development is not always
traceable due to dormancy of seed itself.
In many of the spring wild plants the
germination of seed takes place but the
growth is restricted due to establishment
of young roots. This dormancy often broken
by exposure to low temperature.

6. CAUSES OF THE SEED DORMANCY
The dormancy of seed may be either due to single or a many
different factors. As stated earlier, it may be seed coat-induced
dormancy or embryo induced dormancy.
Seed Coat Induced Dormancy: The seed coat of most of
the seeds is formed by the integumentary layers of ovules.
Chemically it is composed of a complex mixture of
polysaccharides, hemicelluloses, fats, wax and proteins.
The seed coat induced dormancy may be due to following : water
impermeability, Gas impermeability, Mechanical resistance of
seed coat to the growth of embryo.

7. Embryo-induced Dormancy : Embryo-induced
dormancy may be two kinds.
1. Rudimentary and poorly
developed embryo .
1. Embryo fully developed but
unable to resume growth.
• Dormancy due to Specific Light Requirement
In imbibed Lactuca sativa seeds the germination is stimulated by
red light of 660nm wavelength, while it is inhibited by far-red light
of 730nm wavelength.
• Dormancy due to Germination Inhibitors
In many seeds the dormancy occurs due to presence of germination
inhibitors in seed coats, endosperm, embryos or structures
surrounding them. And A number of chemical substances such as
organic acids, phenolics, tannins, alkaloids, indoles and gibberellins
etc.

8. METHODS OF BREAKING
SEED DORMANCY
Scarification
This method is used for breaking dormancy of seeds caused
by hard seed coats which become impermeable to water and
gases etc. By mechanical scarification, chemical
scarification,
stratification
This method is used to break the dormancy of seeds caused
due to condition of embryo.
Others are : Alternating
temperature, light, pressure,
growth regulators

9. ADVANTAGES OF SEED DORMANCY
• The dormancy of seeds help the plants of temperate zones to
tide over the severe colds.
• The dormancy of seeds due to impermeable seed coats
ensures good chances of survival to the plants of tropical
regions.
• The dormancy of seeds in cereals is most important to
mankind. If these seeds germinate Immediately after harvest,
they will be quite useless for mankind.
• Dormant seeds and organs in perennial plants resist
unfavorable condition for their Development.
• The seeds form a measure of the quantity and duration of
rainfall, both of which determine the amount of soil-moisture
available for plant growth.

10. GERMINATION
Changes during seed germination: Seed germination
starts with the imbibitions of water which Increases the
respiration rate rapidly.
Light dependent germination : in many seeds, the seed
germination depends upon light. The seeds contain a
photoreceptor pigment.

11. CHANGES IN FOOD RESERVES
ETCCarbohydrates : The cereal endosperms usually starch as
carbohydrate reserve which during germination is hydrolyzed into
maltose by two enzymes.
Lipids : The seeds with high lipid reserves triglyceride content show
loss during Germination.
At first the lipids are hydrolyzed by lipases at neutral pH.
Protiens : storage proteins in seeds are hydrolyzed during germination
into their constituent amino acids and amides through proteolytic
enzymes especially peptidases.
Nucleic acids : In storage tissues of seeds, the nucleic acid content
usually does not change during germination. However, the increase
in DNA and RNA content of embryonic axis has been recorded in
germination.

12. FACTORS AFFECTING GERMINATION
Water : The water is an important factor which controls and activates
Various enzymatic activities. It help the seeds in imbibitions causing
increase in osmotic effects.
Atmospheric composition : it also affects seed germination. The
atmosphere consists of several gases like oxygen, Co2, etc. Oxygen
increases respiration.
Temperature: The optimum temperature for seed germination varies
according to species.
Soil condition : The soil condition which induce germination include
water holding capacity, aeration of soil , mineral composition,
soil texture, pH of soil and organic matter etc.
Seed structure : sometimes the seeds contain such structures
which inhibit germination. Hard coat may be impermeable to water
and gases.

13. Thank
you