Seed dormancy - class-VII

The fertilized ovule is got dormant so that the adequate amount of endosperm is formed as for division and for further survival, it is very necessary that ample amount of food is present in the seed.

Dormancy of seeds could be broken by the activation of digestive enzymes like alpha amylases. It is being done by phytohormones like gibberellic acid. It also helps in cell elongation, division of lateral meristem and many more.

Only hormone which  induce and maintain seed dormancy is ABA (abscisic acid).

Gibberellin are involved in seed germination in certain plants. They break seed dormancy by promoting mobilisation of reserve food material. In a classic experiment involving barley seed germination, researchers showed that the release of gibberellin from the embryo triggers the synthesis of $\alpha$-amylase, an enzyme that digests starch in the endosperm. As a result, glucose becomes available for absorption by the embryo. Although enzymes mobilize starch reserves in many types of seeds, gibberellin control of seed enzymes appears restricted to cereals and other grasses. 

Seed dormancy is an adaptation to ensure its germination during favourable period. One important function of most seeds is delayed germination, which allows time for dispersal and prevents germination of all the seeds at the same time. The staggering of germination safeguards some seeds and seedlings from suffering damage or death from short periods of bad weather or from transient herbivores; it also allows some seeds to germinate when competition from other plants for light and water might be less intense. Seed dormancy can be caused by all the factors mentioned. A dormant seed is one that is unable to germinate in a specified period of time under a combination of environmental factors that are normally suitable for the germination of the non-dormant seed. Dormancy is a mechanism to prevent germination during unsuitable ecological conditions, when the probability of seedling survival is low. 
Thus, the correct answer is option B.

Stratification involves the treatment of seeds at low temperature (5-10 degree C) under sufficiently moist conditions to break its dormancy and to induce germination.

Dormancy is defined as the condition of seed when it fails to germinate even though the envoirnment condtions, usually considered favourable for active growth, are present.

A. Ethylene serves as a hormone in plants. It acts at trace levels throughout the life of the plant by stimulating or regulating the ripening of fruit, the opening of flowers, and the abscission (or shedding) of leaves.

B. Cytokinins are plant hormones that cause increased celldivision by stimulating the process of mitosis. 

C. Abscisic acid owes its names to its role in the abscission of plant leaves. In preparation for winter, ABA is produced in terminal buds. This slows plant growth and directs leaf primordia to develop scales to protect the dormant buds during the cold season.

So, the correct answer is 'Abscisic acid'.

Germination Inhibitors: They occur in the seed coats and cotyledons of the embryos. The important germination inhibitors causing seed dormancy are abscisic acid, phenolic acid, ferulic acid, coumarin, short fatty acids and cyanogenic chemicals, e.g., Apple, Peach, Ash, Cucurbita, Iris, Xanthium. Counteracting Inhibitors: Inhibitors are destroyed by dipping seeds in KNO$ _3$, thiourea, ethylene chlorohydrin and gibberellin. IBA, GA, ethylene are counteracting inhibitors of seed dormancy while ferulic acid is a germination inhibitor. So, the correct answer is 'Ferulic acid'.

Gibberellins (GA) are well-known plant hormones that promote seed germination and are effective in breaking seed dormancy.

A. Scarification: Hard, impermeable seed coat is weakened or ruptured by filing, chip­ping, hot water 

B. Vernalisation- The cooling of seed during germination in order to accelerate flowering when it is planted.

C Impaction- It means to strike something with force. This method implies to the vigorous shaking of the seeds

D. Stratification: Seeds are moistened and exposed to oxygen for variable period at very low (chilling) or high temperature.

So, the correct answer is 'Stratification'.

Thiourea acts as a chemical agent that helps break seed dormancy by counteracting the effects of germination inhibitors present in the seed.

Quiescence is a condition in which seeds do not germinate due to unfavourable environmental conditions. When favrouable conditions return, the seed will germinate. Seeds of some plants do not germinate even under favourable conditions. This is called as dormancy. It is under endogenous control.

Abscisic acid (ABA) is the primary plant hormone responsible for inducing and maintaining seed dormancy to prevent premature germination.

Reasons of seed dormancy:

1.

<span>Immaturity

of embryo: Embryo is immature at the time of seed shedding. The seed
will remain dormant till the embryo becomes mature, e.g.,
Anemone nemorosa, Ranunculus ficaria.

2. After-Ripening: The seeds require a period of dry storage for developing the ability to germinate, e.g., Wheat, Oat, Barley.

3.

<span>Impermeable seed coat:&nbsp;The seed coat is impermeable to water and gases,

e.g., Apple, Chenopodium.

4.

<span>Hard

seed coat: The seed coat is mechanically resistant and does not
allow the embryo to grow, e.g., Amaranthus,
Lepidium.

5. Germination Inhibitors: They occur in the seed coats and cotyledons of the embryos. The important germination inhibitors causing seed dormancy are abscisic acid, phenolic acid, ferulic acid, coumarin, short fatty acids and cyanogenic chemicals, e.g., Apple, Peach, Ash, Cucurbita, Iris, Xanthium.

So, the correct answer is ‘Hard impermeable seed coat’.

Lettuce seeds are photoblastic and require exposure to red light to trigger the phytochrome system, which breaks dormancy and initiates germination.

Seed dormancy is an adaptive mechanism that prevents germination during unfavorable environmental conditions, ensuring the plant germinates only when conditions are suitable for survival.

A. Stratification: Seeds are moistened and exposed to
oxygen for variable period at low or high temperature.

B. Scarification: Hard, impermeable seed coat is weakened or ruptured
by filing, chip­ping, abosrbing hot water.

C. Vernalisation- The cooling of seed during
germination in order to accelerate flowering when it is planted.

Rhizophora is a mangrove plant that exhibits vivipary, where seeds germinate while still attached to the parent plant, thus lacking seed dormancy.

• Stratification involves the treatment of seed at low temperature(5−10 C)

Scarification in the method of weakening and opening the seed coat to initiate germination. It makes seed coat permeable. This method is employed for plant species which are impervious to water and gases.

Vernalization (often misspelled as verbalization) is the induction of a plant's flowering process by exposure to the prolonged cold of winter, typically in the range of 0 to 4 degrees Celsius.

Allelopathy involves the production of chemicals by plants that influence the growth of other plants. Statements 1, 2, and 3 correctly describe aspects of this phenomenon, including germination inhibition and spacing.

Dormancy period is an inactive state of seed. To break down this state, seed require the favourable environment in which temperature and water play a major role to increase the metabolism as enzymes work on certain temperature and water breaks the seed coat by imbibition.

As a viviparous plant, Rhizophora creates a propagule that is in reality a living tree. Though resembling an elongated seed pod, the fully-grown propagule on the mangrove is capable of rooting and producing a new tree. The trees are hermaphrodites, capable of self pollination or wind pollination. The tree undergoes no dormant stage as a seed, but rather progresses to a live plant before leaving its parent tree. A mangrove propagule may float in brackish water for over a year before rooting. So, the correct answer is 'Rhizophora'.

Escape in time refers to strategies like dormancy, diapause, or hibernation that allow organisms to survive unfavorable periods. The Arctic tern is a migratory bird, which is an example of escape in space.

Scarification involves weakening, opening or altering the coat of a seed to encourage the germination. It can be done mechanically, thermally and chemically. This will make the seed coat permeable for water and air, which will help in germination of seeds.

Seed dormancy allows seeds to overcome periods that are unfavourable for seedling established and is therefore important for plant ecology and agriculture. Several processes are known to be involved in the induction of dormancy and in the switch from the dormant to the terminating state. Imbibition is a special type of diffusion when water is absorbed by solids-colloids causing an enormous increase in volume. If it were not for the pressure due to imbibition, seedlings would not have been able to emerge out of the soil into the open; they probably would not have been able to establish.

Seed dormancy is induced in plants under unfavorable condition due to growth inhibitor hormone-like abscisic acid. Gibberellin is most commonly used to breaks the seed dormancy and induce flowering under normal condition. Apart from this, other chemicals are used to break the seed dormancy. These chemicals include potassium nitrate (KNO$ _3$), thiourea and ethylene chlorhydrin.