germination cycle 3

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Growth Development and Reproduction Booklet

Germination is the stage in the plant life cycle when growth of a new plant begins from a seed Germination begins when the seed takes up water (imbibition) and the seed coat cracks A seed is a dry inactive embryonic plant complete with a reserve of stored energy to keep it alive and sustain germination

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How does germination start?
Germination begins with activation by water uptake. We call this imbibition, and sometimes the seed or fruit requires special treatment for water to get into the seed and start this process. We often use the emergence of the (the embryonic root) from the seed coat as a measure of successful germination.
What is the difference between Phase 1 and Phase 3 germination?
Initially, there is a rapid imbibition of water by a dry seed (phase I) until the seed tissues are fully hydrated. This is followed by a limited water uptake during phase II, whereas in phase III, there is an increase of water uptake that is related to the completion of germination.
What happens during germination in a quiescent seed?
The cell cycle, which is arrested in a quiescent seed, is reversed during germination. The replication of DNA is a relatively late event in seedling formation, and it occurs after a seed imbibes water at the end of phase II.
How is the cell cycle monitored during seed germination?
Flow cytometry was also performed to monitor the progression of the cell cycle during seed germination. Embryos were analysed from 4 to 24 HAI. Based on the histograms, the percentage of cell nuclei in specific phases (G1, S, G2) was determined using the Cell Cycle Analysis function in FlowMax software, which is summarised in Table 1.

Overview

germination, the sprouting of a seed, spore, or other reproductive body, usually after a period of dormancy. The absorption of water, the passage of time, chilling, warming, oxygen availability, and light exposure may all operate in initiating the process. In the process of seed germination, water is absorbed by the embryo, which results in the rehydration and expansion of the cells. Shortly after the beginning of water uptake, or imbibition, the rate of respiration increases, and various metabolic processes, suspended or much reduced during dormancy, resume. These events are associated with structural changes in the organelles (membranous bodies concerned with metabolism), in the cells of the embryo. britannica.com

Seed dormancy

Dormancy is brief for some seeds—for example, those of certain short-lived annual plants. After dispersal and under appropriate environmental conditions, such as suitable temperature and access to water and oxygen, the seed germinates, and the embryo resumes growth. The seeds of many species do not germinate immediately after exposure to conditions generally favourable for plant growth but require a “breaking” of dormancy, which may be associated with change in the seed coats or with the state of the embryo itself. Commonly, the embryo has no innate dormancy and will develop after the seed coat is removed or sufficiently damaged to allow water to enter. Germination in such cases depends upon rotting or abrasion of the seed coat in the gut of an animal or in the soil. Inhibitors of germination must be either leached away by water or the tissues containing them destroyed before germination can occur. Mechanical restriction of the growth of the embryo is common only in species that have thick, tough seed coats. Germination then depends upon weakening of the coat by abrasion or decomposition. In many seeds the embryo cannot germinate even under suitable conditions until a certain period of time has lapsed. The time may be required for continued embryonic development in the seed or for some necessary finishing process—known as afterripening—the nature of which remains obscure. Are you a student? Get Britannica Premium for only $24.95 - a 67% discount Subscribe Now The seeds of many plants that endure cold winters will not germinate unless they experience a period of low temperature, usually somewhat above freezing. Otherwise, germination fails or is much delayed, with the early growth of the seedling often abnormal. (This response of seeds to chilling has a parallel in the temperature control of dormancy in buds.) In some species, germination is promoted by exposure to light of appropriate wavelengths. In others, light inhibits germination. For the seeds of certain plants, germination is promoted by red light and inhibited by light of longer wavelength, in the “far red” range of the spectrum. The precise significance of this response is as yet unknown, but it may be a means of adjusting germination time to the season of the year or of detecting the depth of the seed in the soil. Light sensitivity and temperature requirements often interact, the light requirement being entirely lost at certain temperatures. britannica.com

Seedling emergence

Active growth in the embryo, other than swelling resulting from imbibition, usually begins with the emergence of the primary root, known as the radicle, from the seed, although in some species (e.g., the coconut) the shoot, or plumule, emerges first. Early growth is dependent mainly upon cell expansion, but within a short time cell division begins in the radicle and young shoot, and thereafter growth and further organ formation (organogenesis) are based upon the usual combination of increase in cell number and enlargement of individual cells. Until it becomes nutritionally self-supporting, the seedling depends upon reserves provided by the parent sporophyte. In angiosperms these reserves are found in the endosperm, in residual tissues of the ovule, or in the body of the embryo, usually in the cotyledons. In gymnosperms food materials are contained mainly in the female gametophyte. Since reserve materials are partly in insoluble form—as starch grains, protein granules, lipid droplets, and the like—much of the early metabolism of the seedling is concerned with mobilizing these materials and delivering, or translocating, the products to active areas. Reserves outside the embryo are digested by enzymes secreted by the embryo and, in some instances, also by special cells of the endosperm. In some seeds (e.g., castor beans) absorption of nutrients from reserves is through the cotyledons, which later expand in the light to become the first organs active in photosynthesis. When the reserves are stored in the cotyledons themselves, these organs may shrink after germination and die or develop chlorophyll and become photosynthetic. Environmental factors play an important part not only in determining the orientation of the seedling during its establishment as a rooted plant but also in controlling some aspects of its development. The response of the seedling to gravity is important. The radicle, which normally grows downward into the soil, is said to be positively geotropic. The young shoot, or plumule, is said to be negatively geotropic because it moves away from the soil; it rises by the extension of either the hypocotyl, the region between the radicle and the cotyledons, or the epicotyl, the segment above the level of the cotyledons. If the hypocotyl is extended, the cotyledons are carried out of the soil. If the epicotyl elongates, the cotyledons remain in the soil. britannica.com

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Qu'est-ce que la germination PDF ?
La germination
La germination correspond à l'étape par laquelle une semence en vie ralentie "se réveille" et donne naissance à une plantule, ce passage met en jeu des mécanismes physiologiques complexes qui vont du début de l'hydratation de la semence à la croissance de la radicule.
Quelles sont les étapes de germination ?
La germination se réalise en trois phases :
la phase d'imbibition, c'est-à-dire la phase d'absorption de l'eau par la graine ;la phase de forte activité métabolique, où les réserves de la graine sont transformées afin de pouvoir être utilisées par la plantule ;l'émergence de la radicule.
Comment germent et poussent les plantes cycle 3 ?
Pour germer, les graines ont besoin d'eau et d'une température favorable. Pour bien se développer, les plantes ont besoin de lumière, d'eau, d'une température favorable et d'un support tel que le terreau.
1. Début du développement d'un nouvel individu végétal, à partir d'une graine placée dans les conditions favorables. 2. Passage à l'état de vie active d'un organe clos dont la vie a été jusque-là très ralentie (spore, œuf, tubercule).

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Quelles sont les différentes étapes de la germination ?

Que se passe-t-il ? Il faut planter une graine dans la terre puis l'arroser.
. La graine s'ouvre pour laisser sortir la plante (étape de germination) ; elle sort de la terre, accrochée à la tige, et se casse en deux (étape de levée) puis elle tombe et la plante continue à grandir (étape de croissance).

Comment expliquer la germination ?

Ouvrir des graines en deux après les avoir laissées tremper dans l'eau quelques heures et les faire observer à l'enfant.
. Dans les plus grosses, comme par exemple les graines de haricots, on voit très distinctement le germe de la future plantule.
. Si vous disposez d'une loupe, faites-lui observer.

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