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Seed dormancy and germination-plant physiology

Byprakash

Seed dormancy and seed germination

seed dormancy and seed germination are the crucial steps in a life cycle of a plant. 



Having detailed knowledge about seed dormancy and seed germination can helps us to know physiology of plants and helps us to increase our production.


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Seed dormancy and seed germination 



 This article is divided into 2 parts. In part-1, we will discuss about seed dormancy and in part-2, we will discuss about seed germination.


    Seed Dormancy

    We know the meaning of dormancy is rest or lacking of any metabolic activities.

    On this reference, Seed dormancy can be defined as the failure of viable seed to germinate into a seedling even under the favourable environmental condition.

    For seed dormancy, to be called such there must be viable seed and suitable condition to germinate.

    Types Of Seed Dormancy

    Seed dormancy is classified on the basis of what actually causes the dormancy.

     There are 3  types of seed dormancy which are:-

    1.Imposed dormancy:- imposed means these factors are acted upon seed. It is due to external parameters that acts on seed.

    2.Innate dormancy:- Innate means within. Some growth inhibitors within the seed arrest its growth even in favourable condition.

    3.Secondary dormancy:-Many crops capable of germinating immediately after ripening but  pass to dormant phase, this is called as secondary dormancy.

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    Causes Of Seed Dormancy

    1.Outer seed coat

    a.Impermeable seed coat:- Due to impermeable seed coat water and O2 cannot enter the  seed and fails to germinate and goes under dormant phase.

    b.Mechanical (Hard seed coat) resistance:-
    Some seeds have very hard seed coat due to which radicle and plumule cannot break seed coat and fails to germinate.

     In this, even if seed imbibes water, embryo cannot expand to fixed seed coat and all metabolic activities stops and seed automatically goes under dormant phase.

    c.Chemical growth inhibitors:-

     seed may contains growth inhibitors in seed coat or even inside seed coat. These chemical inhibitors causes dormancy of seed. Some example of chemical inhibitor are ABA(absissic acid).

    Other Causes Of Dormancy

    a.phisiologically shallow dormancy:- present in some freshly harvested seed. Disappears with dry storage over a period of days or months.

    b.Light dormancy:-Some species have exact requirements of light quality, quantity and duration to induce germination.

    c.Temperature dormancy:-Many seeds are specific in their temperature requirements. Some need alternating  temperatures.

    Others germinate over a narrow range of temperatures and go dormant above or below this range.

    d. Physiologically deep dormancy:- seeds are unable to germinate until they undergo a cool-moist period over few days or few months.

    3.Exogenous dormancy:-

    Till now, we have got knowlege about internal dormancy. Not only internal but there are some factors which act outside the embryo which caused dormancy. 
    These type of dormancy causing factors are outside embryo but inside seed coats. So lets learn its types:-

    a. Physical(Outer part) dormancy

    It is a type of dormancy in seed which occurs due to impermeable seed coat. If a seed has hard seed coat then water and O2 cannot enters into seed due to which seed cannot germinate and goes into dormant phase.

    b.Mechanical(Hardness) dormancy

    ~Mechanical dormancy is similar to physical dormancy i.e it is also due to outer hard coverings. But in this dormancy, embryo becomes unable to expand due to which seed cannot germinate and goes into dormant phase.

    c.chemical inhibitors  dormancy

    ~Different types of growth inhibitors are present within the seed and on seed coat which suppresses growth of seedling and seeds becomes dormant.

    These type of dormancy can be overcomed by leaching out those chemcals. For this we can soak seed in hot water or in solution having high concentration than cell sap which causes exo-osmosis or chemicals.

    Till now, we have discussed about different factors which causes seed dormancy. All above explained factors acts outside embryo of seed but inside and on seed coat.

    Internal Factors Causing Seed Dormancy

    a. Physiological dormancy/Dormancy due to chemical changes.

    ~In this type of dormancy, seed is unable to germinate into new seedling because there is no any physiological or chemical changes inside the seed.

    For seed to germinate there must be chemical changes. For example:-increase in GA3 causes amylase production which hydrolyses carbohydrate and provides nutrition for germination.

    So,we can say that sometime seed doesn’t germinate until chemical changes occurs within the seed.

    b.Morphological dormancy/Dormancy due to undeveloped embryo

    For seed to germinate, embryo must be mature enough. This is because, embryo undergoes division and gives rise to radical and plumule which is th intial  step of germination.

    Sometimes, embryo inside seed doesn’t mature enough due to different condition and causes seed dormancy. Some seeds embryo goes on maturing even after harvesting. So sowing seed without storage for some period can cause morphological dormancy.

    c.Combined dormancy

    Sometimes both internal and external factors acts on seed and causes dormancy which is called combined dormancy.

    Breaking Of Seed Dormancy

    Seed dormancy has much more negative effects on production of certain crops. so, seed dormancy should be break in order to get lot of production.

    Some of the methods of breaking seed dormancy are discussed below:-

    1.Seed scarification

    scarification simply means making scars on something. So, seed scarification means  scratching of hard seed coat.

     It can be done by rubbing with sandpaper or with knife. Sometimes acid and hot water can also be used to make scarification.

     Seed which are scarfied grows much faster than normal seed. Try it on bitter gourd for excellent results and comparision.

    2.Seed stratification

    Stratification means giving cold or chilling treatment to the seeds before sowing. Some seeds needs chilling treatment otherwise they do not germinate. 

    For example, apple seed should be stored in (1-5)०c for their good germination.


    3.Light exposure

    some seeds needs light to break dormancy. These type of seed which needs lights to germinate are called positively photoblastic seeds. These seeds should be shallowly swoed for their good germination rate.

    4.other method

    ~soaking seeds in hot water
    ~By vigorously shaking seeds.
    ~ pressure treatement etc…

    Importance Of Seed Dormancy

    Now that, we have learned about seed dormancy, it is necessary to know about its importance.

    Most of the importance of seed dormancy is that:- We can store the seed for longer period of time due to its nature. We can use grains for our feed. It also helps to maintain food security within the country.
    So we have learned the detailed explanation on seed dormancy.

    Hope you guys gets the answer you want. Thank you for reading this article with this much attention.

    As we have finished learning about seed dormancy, let’s move towards seed Germination.
    The second part of detailed explanation on seed dormancy and seed germination begins from here.

    We have provided detailed explanation on seed germination, steps of seed germination and types  of seed germination.

    So, read the article till end to have complete package of knowledge.

    Here, we haven’t discussed about the factors affecting the seed germination as it is whole lot of topic.

     So, we will discuss about it on next article with full detail. So, now let’s jump to grab the information on Seed Germination.

    Seed Germination

    Seed germination basically means the growth of seed. Growth into what??- Growth into seedling.If we explained it on more scientific way, the definition on seed germination is given below:-

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    Seed germination can be defined as the resumption of metabolic activities of dormant seed resulting in emergence of radical and plumule and ultimately into young seedling.
    Seed germination is crucial stage in life cycle of plant. 

    So, there should be given attention in use of fertilizers, irrigation and many other things during germination of seeds.

    If we didn’t give special attention at this phase, we might get huge loss in production of crops.

    There are certain steps in germination of seed. 
    Now, let’s learn about the steps of seed germination:-

    1.Imbibation of water

    This is the first step of seed germination. After the seed is sown to soil, it absorbs water from soil. After adsorbing water, the seed swells  up. Then O2 also enters into seed.

    2.Activation of enzymes

    As soon as the seed imbibes water, different enzymes such as amylase gets activated. These enzymes starts to act on stored food materials.

    3.Breakdown of complex food materials

    Enzymes acts upon complex food materials and converts them into simpler form such as glucose. Embryo uses these energy and start to divide and forms different many cells

    4.Formation of radicle and plumule

    After the use of energy and division of embryo, new structures of radicle and plumule forms and they moves towards seed coat.

    5.Rupture of seed coat and emergence of radicle and plumule

    Finally, outer seed coat ruptures and plumule emerges out of seed coat which later forms shoot system. Similarly, Radicle also emerges out of seed coat towards downward which later develops into root system.

    6.Emergence of seedling

    At last seedling emerges and new plant is formed.

    In this way the seeds germinate with different physiological and biochemical changes within seed.

    Types Of Seed Germination

    Germination of seed is classified into two types based on movement of cotyledon below or above the soil.

    There are 2 types of germination of seed which are discussed below:-

    1.Epigeal germination

    Epi means above, so in this type of germination  cotyledons rise above the soil surface.

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    Epigeal germination of seed
    In this type of germination hypocotyl elongates which pushes cotyledons above soil surface.
    Most of the dicots have epigeal germination(@ed)

    2Hypogeal germination

    Hypo means below, so in this type of germination cotyledons remains below soil surface.

    seed dormancy,seed germination,seed dormancy in hindi,germination of seed,seed,seed germination animation,seed dormancy definition,seed dormancy definition biology,seeds,seed dormancy in hindi (bsc ad 1st sem),dormancy,germination of seeds,seed dormancy in plants,reasons for seed dormancy,in hindi seed dormancy,seed dormancy video,types of seed dormancy,seed dormancy lecture,seed parts and functions
    Hypogeal germination of seed
    In this type of germination epicotyl elongates.
    All monocots and few dicots have hypogeal germination.
    SO, This is the detailed explanation on seed dormancy and seed germination. Hope you like this article.

    Please comment your reviews on this.

    Note:-Factors affecting Germination will be uploded with full explanation within few days in this blog.

    Thank you!😊

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