There two type of seeds for light sensitivity:

promotes germination in lettuce seeds.

Cotton seed pericarp contains? Coriander seed pericarp contains? Paddy hull contain?

seed sensitivity to heat or cold. Some seeds germinate only at high temperature. like Amaranth.

The dormancy due to conditions within the dormant plant or organ is called

IN NATURE, CERTAIN ENVIRONMENTAL AGENTS SOFTEN SEED COATS:

prevents embryo growth and seed germination until chemical changes occur.

Altering temperature treatment

According to C. Baskin and J. Baskin (1998; 2004) have proposed a comprehensive classification system which include five classes of seed dormancy

There are main two types of overcoming of seed dormancy:

Morphological dormancy can be divided into two types

Seeds of some species like lettuce remain dormant in the dark, they germinate when they are exposed to light.

Oxygen deficiency leads to inhibition of ___________ activity which leads to dormancy.

includes treating seeds with strong acids and organic solvents. E.g. Sulphuric acid.

The dormancy of seeds due to rudimentary or complete dormant embryo is called

This minimizes metabolic activity and therefore helps an organism to conserve to energy.

have been used to induce germination in positively photoblastic seeds like lettuce and tobacco etc.

Endogenous dormancy

not active or growing but able to become active later.

Seeds of some species like Phlox, Nemophila and Silene remain dormant when exposed to light. They germinate only in the dark.

FACTORS AFFECTING THE LIFE SPAN OF SEEDS

➤Dormancy causing hormones are

Mechanism of Dormancy

➤Treatment of seed at low temperature under moist condition. ➤ During this anatomical and biochemical changes takes place in the seed. ➤Growth promoting hormones increases and Growth retarding hormones decreases.

the embryo is underdeveloped or undifferentiated.

It is the incapacity of fully developed, mature, viable seed to germinate even under favourable conditions.

reported the seed germination in certain plants like sweet clover (Melilotus alba) and alfalfa (Medicago sativa) can be greatly improved after being subjected to hydraulic pressure of about 2000 atm. at 18°C for about 5-20 minutes.

It is process of shaking of seeds to clear blockage of testa pores. E.g. Seeds of Crotolaria egyptica (legume)

Methods of Breaking the Seed Dormancy

Seed coats are impermeable in water due to macrosclereid cells, mucilaginous outer cell layer or hardened endocarp. ➤ Depth of the puncture to the seed coat increased, so did the permeability of seed coat of water. ➤ E.g., Olive, Peach, Plum, (hardened endocarp of seed).

provides a mechanism for plants to delay germination until conditions are optimal for survival of the next generation (Finkelstein et al. 2008).

During the developmental cycle of the plant, at some phase certain structures like buds, tubers, seeds, go though a period of temporary suspension of growth activity or slow down for a period of time or deep sleep, such a state is called ?

Low temp. treatment/ stratification

light sensitivity affects germination of some seeds. These photoblastic seeds need a period of darkness or light to germinate.

In order to remove the plugs the seeds are shaken vigoursly and this treatment is known as?

Mechanical dormancy occurs when seed coats or other coverings are too hard to allow the embryo to expand during germination.

Classification of seed dormancy

defined dormancy as any phase in the life cycle of a plant in which active growth is temporarily suspended.

is defined as a state in which seeds are unable to germinate even under environmental conditions normally favorable for germination.

This method is used to break the dormancy of seeds caused due to condition of embryo.

TYPES OF DORMANCY According to wareing (1969) the dormancy may be two types

Studies with ABA and GA biosynthesis and signaling pathway demonstrated that these two hormones have important and antagonistic roles in germination and dormancy respectively.

This class of seed dormancy refers to seed with under development and differentiated embryos, this includes embryos in which the cotyledons and hypocotyls, radical axis are differentiated, but small in size.

TYPES OF SEED DORMANCY Crocker (1916) divided seed dormancy into two types:

Presence of inhibitors within the seed (seed coat) can cause dormancy. E.g.: Cotton seed pericarp contains Abscisic acid Coriander seed pericarp contains Coumarin Paddy hull contain Abscisic acid

Exogenous dormancy

Due to internal causes even if all external environmental conditions are duly present.

The dormancy of seeds due to extreme hardness of seed coat is called

The method is used for breaking dormancy of seeds caused by hard seed coats which become impermeable to water and gases etc. The method employed in softening or weakening the seed coat is called?

Dormancy in seed is controlled by metabolic energy produced in seeds.

When dormancy caused due to external factors like absence of sunlight, CO2, very high or low temperature.

In this class, seeds have embryos that are underdeveloped (in size), but differentiated (e.g., into cotyledons and hypocotyls radical) as well as a physiological component to their dormancy.

only germinate if there is presence of smoke.

When mechanical breaking of seed coat is done at one or more places, it is called ?

includes treating seeds with strong acids and organic solvents. E.g. Sulphuric acid.

High temperature treatment

Stratification: ➤ This method is used to break the dormancy of seeds caused due to condition of embryo. ➤ In this process the seeds are exposed to well aerated, moist conditions under low temperature ______________. This treatment is called Stratification or after-ripening.

The breaking of dormancy

It is a condition in which germination or growth fails to occur even though the external environmental conditions are favourable.

The seed is called ________ and the phenomenon is termed ________.

Dormancy that is caused by an impermeable seed coat. ➤ It is the result of impermeable layer that develops during maturation and drying of the seed or fruit. ➤ It prevents the seed from taking up water or gases. ➤ As a result, the seed is prevented from germinating until dormancy is broken. ➤Generally, physical dormancy is the result of one or more palisade layers in the fruit or seed coat.

induces and maintains seed dormancy during embryo maturation. The key to ABA metabolism are some specific genes encoding key enzymes are of NCED family

These seeds have both morphological and physiological dormancy.

The dormancy due to unfavourable environmental conditions is called

Physiological dormancy prevents embryo growth and seed germination until chemical changes occur.

In such cases, the completely dry ripe seed is physiologically inactive and is said to be in a ?

is done by shaking the seeds with sand or by scratching o nicking the seed coat with knife.

The treatment of seed coat with strong mineral acids or other chemicals is called ?

Factors causing dormancy of seeds

positively regulates ABA synthesis.

ARTIFICIAL OVERCOMING OF SEED DORMANCY

Nature of dormancy stops when the embryo gets appropriate environment such as adaptive moisture and temperature.