ASSIGNMENT ON : SEED DORMANCY
SUBMITTED TO- SUBMITTED BY -
Dr . DEEPIKA SAHU E Swetangini
( Dept of Plant breeding) 2nd year, 2nd sem
CONTENTS
• Introduction
• Mechanism of Dormancy
• Classification
• Factors causing Dormancy
• Methods to Overcome Dormancy
• Biological Importance of Seed Dormancy
Seed Dormancy is
a condition in
which a viable seed
fails to germinate
even when
environmental
conditions (water,
temperature,
oxygen, light) are
favorable.
INTRODUCTION
During the developmental cycle of the plant, at some certain
structures like buds, tubers, seeds, go through a period of
temporary suspension of growth activity, such astate is
called dormancy.
In plant physiology, dormancy is a period of arres
plant growth.
It is an survival strategy exhibited by many plants under
unfavorable conditions.
To overcome unfavorable conditions, lower plants
produces Endospores, Zygospores, Auxospores,..ete
HORMONAL
MECHANISM:
Studies with ABA and GA biosynthesis and
signaling pathway demonstrated that these two
hormones have important and antagonistic roles in
germination and dormancy respectively.
ABA induces and maintains seed dormancy during
embryo maturation. The key to ABA metabolism
are some specific genes encoding key enzymes are
of NCED family (NCED6 and NCED9).
(Nine-cis-epoxy carotenoid dioxygenase.)
Embryonic identity protein (FUS3), which
positively regulates ABA synthesis.
Factors causing Dormancy
1. Hard or Impermeable Seed Coat – prevents water and oxygen from entering
(e.g., legumes).
2. Immature Embryo – embryo not fully developed at seed maturity
(e.g., orchids, ginkgo).
3. Presence of Chemical Inhibitors – like abscisic acid (ABA), phenolics,
coumarins, etc.
4. Mechanical Resistance of Seed Coat – thick/tough coat restricts embryo
expansion (e.g., walnut).
5. Light Sensitivity – some seeds require light (positive photoblastic) or
darkness (negative photoblastic) to germinate (e.g., lettuce, tobacco).
6. Temperature Requirements – some seeds need chilling (cold stratification) or
heat for dormancy break (e.g., apple, wheat).
7. Oxygen Availability – low oxygen concentration around seeds can induce
dormancy.
8. Moisture/Desiccation Conditions – very dry or overly moist conditions at
dispersal can induce dormancy.
Methods to Overcome Dormancy
1. Scarification – Breaking or weakening hard seed coats by mechanical
(rubbing, filing), thermal (hot water), or chemical (acid) treatment.
2. Stratification – Exposing seeds to alternating periods of cold and warm, moist
conditions to simulate natural seasons (e.g., apple, peach).
3. Chemical Treatments – Using chemicals like Gibberellic Acid (GA₃), KNO₃,
thiourea, ethanol to overcome physiological dormancy.
4. Leaching – Washing seeds in running water to remove chemical inhibitors
present in seed coats (e.g., citrus).
5. Light Treatment – Exposing seeds that are light-sensitive (positive
photoblastic) to light (e.g., lettuce, tobacco).
6. Temperature Shock – Exposing seeds to sudden high or low temperatures to
break dormancy (e.g., cereals).
7. Embryo Culture / Seed Coat Removal – Excising the embryo and growing it in
nutrient medium, or manually removing the tough seed coat.
Biological Importance of Seed
Dormancy
• Ensures Survival – Prevents germination during unfavorable conditions (drought, frost,
extreme heat).
• Synchronizes Germination – Seeds germinate only when environmental conditions are
optimal, ensuring better establishment.
• Aids in Seed Dispersal – Provides time for seeds to spread to new habitats before
germination.
• Maintains Seed Bank in Soil – Dormant seeds accumulate in soil, acting as a reserve for
future generations.
• Promotes Genetic Diversity – Different seeds of the same species germinate at different
times, reducing competition.
• Controls Weed Population – In weeds, dormancy ensures persistence in fields, making
them difficult to eradicate.
• Supports Plant Evolution – By delaying germination, species adapt to changing climates
and habitats over time.
