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Germination is the process by which an
organism An organism is any life, living thing that functions as an individual. Such a definition raises more problems than it solves, not least because the concept of an individual is also difficult. Many criteria, few of them widely accepted, have be ...
grows from a seed or
spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
. The term is applied to the
sprouting Sprouting is the natural process by which seeds or spores germination, germinate and put out Shoot (botany), shoots, and already established plants produce new leaves or buds, or other Plant development#Adventitious structures, structures expe ...
of a
seedling A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embry ...
from a
seed In botany, a seed is a plant structure containing an embryo and stored nutrients in a protective coat called a ''testa''. More generally, the term "seed" means anything that can be Sowing, sown, which may include seed and husk or tuber. Seeds ...
of an
angiosperm Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed within a fruit ...
or
gymnosperm The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...
, the growth of a
sporeling A sporeling is a young plant or fungus produced by a germinated spore, similar to a seedling derived from a germinated seed. They occur in algae, fungi, lichens, bryophytes and seedless vascular plants. Sporeling development Most spores germin ...
from a
spore In biology, a spore is a unit of sexual reproduction, sexual (in fungi) or asexual reproduction that may be adapted for biological dispersal, dispersal and for survival, often for extended periods of time, in unfavourable conditions. Spores fo ...
, such as the spores of
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
, ferns,
bacteria Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one Cell (biology), biological cell. They constitute a large domain (biology), domain of Prokaryote, prokaryotic microorganisms. Typically a few micr ...
, and the growth of the
pollen tube A pollen tube is a tubular structure produced by the male gametophyte of seed plants when it germinates. Pollen tube elongation is an integral stage in the plant life cycle. The pollen tube acts as a conduit to transport the male gamete cells fr ...
from the
pollen grain Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains h ...
of a
seed plant A seed plant or spermatophyte (; New Latin ''spermat-'' and Greek ' (phytón), plant), also known as a phanerogam (taxon Phanerogamae) or a phaenogam (taxon Phaenogamae), is any plant that produces seeds. It is a category of embryophyte (i.e. la ...
.


Seed plants

Germination is usually the growth of a plant contained within a seed resulting in the formation of the seedling. It is also the process of reactivation of metabolic machinery of the seed resulting in the emergence of
radicle In botany, the radicle is the first part of a seedling (a growing plant embryo) to emerge from the seed during the process of germination. The radicle is the embryonic root of the plant, and grows downward in the soil (the shoot emerges from t ...
and
plumule A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embry ...
. The seed of a
vascular plant Vascular plants (), also called tracheophytes (, ) or collectively tracheophyta (; ), are plants that have lignin, lignified tissues (the xylem) for conducting water and minerals throughout the plant. They also have a specialized non-lignified Ti ...
is a small package produced in a
fruit In botany, a fruit is the seed-bearing structure in flowering plants (angiosperms) that is formed from the ovary after flowering. Fruits are the means by which angiosperms disseminate their seeds. Edible fruits in particular have long propaga ...
or
cone In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the '' apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines ...
after the union of male and female
reproductive cells A gamete ( ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. The name gamete was introduced by the Ger ...
. All fully developed seeds contain an
embryo An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...
and, in most plant species some store of food reserves, wrapped in a seed coat. Dormant seeds are viable seeds that do not germinate because they require specific internal or environmental stimuli to resume growth. Under proper conditions, the seed begins to germinate and the embryo resumes growth, developing into a seedling. Disturbance of soil can result in vigorous plant growth by exposing seeds already in the soil to changes in environmental factors where germination may have previously been inhibited by depth of the seeds or soil that was too compact. This is often observed at gravesites after a burial. Seed germination depends on both internal and external conditions. The most important external factors include right
temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...
,
water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
,
oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...
or
air An atmosphere () is a layer of gases that envelop an astronomical object, held in place by the gravity of the object. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosph ...
and sometimes
light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
or
darkness Darkness is the condition resulting from a lack of illumination, or an absence of visible light. Human vision is unable to distinguish colors in conditions of very low luminance because the hue-sensitive photoreceptor cells on the retina a ...
. Various plants require different variables for successful seed germination. Often this depends on the individual seed variety and is closely linked to the ecological conditions of a plant's
natural habitat In ecology, habitat refers to the array of resources, biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species' habitat can be seen as the physical manifestation of its ...
. For some seeds, their future germination response is affected by environmental conditions during seed formation; most often these responses are types of
seed dormancy Seed dormancy is an evolutionary adaptation that prevents seeds from germinating during unsuitable ecological conditions that would typically lead to a low probability of seedling survival. Dormant seeds do not germinate in a specified period of ...
. * Water is required for germination. Mature seeds are often extremely dry and need to take in significant amounts of water, relative to the dry weight of the seed, before cellular
metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
and growth can resume. Most seeds need enough water to moisten the seeds but not enough to soak them. The uptake of water by seeds is called
imbibition Imbibition is a special type of diffusion that takes place when liquid is absorbed by solids-Colloid, colloids causing an increase in volume. Water surface potential movement takes place along a concentration gradient; some dry materials absorb ...
, which leads to the swelling and the breaking of the seed coat. When seeds are formed, most plants store a food reserve with the seed, such as
starch Starch or amylum is a polymeric carbohydrate consisting of numerous glucose units joined by glycosidic bonds. This polysaccharide is produced by most green plants for energy storage. Worldwide, it is the most common carbohydrate in human diet ...
,
protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...
s, or
oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...
s. This food reserve provides nourishment to the growing embryo. When the seed imbibes water,
hydrolytic enzyme In biochemistry, hydrolases constitute a class of enzymes that commonly function as biochemical catalysts that use water to break a chemical bond: :\ce \quad \xrightarrowtext\quad \ce This typically results in dividing a larger molecule into sm ...
s are activated which break down these stored food resources into metabolically useful
chemical A chemical substance is a unique form of matter with constant chemical composition and characteristic properties. Chemical substances may take the form of a single element or chemical compounds. If two or more chemical substances can be combin ...
s. After the seedling emerges from the seed coat and starts growing roots and leaves, the seedling's food reserves are typically exhausted; at this point
photosynthesis Photosynthesis ( ) is a system of biological processes by which photosynthetic organisms, such as most plants, algae, and cyanobacteria, convert light energy, typically from sunlight, into the chemical energy necessary to fuel their metabo ...
provides the energy needed for continued growth and the seedling now requires a continuous supply of water, nutrients, and light. * Oxygen is required by the germinating seed for
metabolism Metabolism (, from ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cellular processes; the co ...
. Oxygen is used in
aerobic respiration Cellular respiration is the process of oxidizing biological fuels using an inorganic electron acceptor, such as oxygen, to drive production of adenosine triphosphate (ATP), which stores chemical energy in a biologically accessible form. Cellu ...
, the main source of the seedling's energy until it grows leaves. Oxygen is an
atmospheric gas The atmosphere of Earth is composed of a layer of gas mixture that surrounds the Earth's planetary surface (both lands and oceans), known collectively as air, with variable quantities of suspended aerosols and particulates (which create weather ...
that is found in
soil Soil, also commonly referred to as earth, is a mixture of organic matter, minerals, gases, water, and organisms that together support the life of plants and soil organisms. Some scientific definitions distinguish dirt from ''soil'' by re ...
pore spaces; if a seed is buried too deeply within the soil or the soil is waterlogged, the seed can be oxygen starved. Some seeds have impermeable seed coats that prevent oxygen from entering the seed, causing a type of physical dormancy which is broken when the seed coat is worn away enough to allow gas exchange and water uptake from the environment. ** In a small number of plants, such as
rice Rice is a cereal grain and in its Domestication, domesticated form is the staple food of over half of the world's population, particularly in Asia and Africa. Rice is the seed of the grass species ''Oryza sativa'' (Asian rice)—or, much l ...
, anaerobic germination can occur in waterlogged conditions. The seed produces a hollow
coleoptile Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses in which few leaf primordia and shoot apex of monocot embryo remain enclosed. The coleoptile protects the first leaf as well as the growing ...
that acts like a 'snorkel', providing the seed with access to oxygen. * Temperature affects cellular metabolism and growth rates. Seeds from different species and even seeds from the same plant germinate over a wide range of temperatures. Seeds often have a temperature range within which they will germinate, and they will not do so above or below this range. Many seeds germinate at temperatures slightly above 60–75 F (16–24 C) oom-temperature in centrally heated houses while others germinate just above freezing and others germinate only in response to alternations in temperature between warm and cool. Some seeds germinate when the soil is cool 28–40 F (-2 – 4 C), and some when the soil is warm 76–90 F (24–32 C). Some seeds require exposure to cold temperatures (
vernalization Vernalization () is the induction of a plant's flowering process by exposure to the prolonged cold of winter, or by an artificial equivalent. After vernalization, plants have acquired the ability to flower, but they may require additional season ...
) to break dormancy. Some seeds in a dormant state will not germinate even if conditions are favorable. Seeds that are dependent on temperature to end dormancy have a type of physiological dormancy. For example, seeds requiring the cold of winter are inhibited from germinating until they take in water in the fall and experience cooler temperatures. Cold stratification is a process that induces the dormancy breaking prior to light emission that promotes germination . Four degrees Celsius is cool enough to end dormancy for most cool dormant seeds, but some groups, especially within the family
Ranunculaceae Ranunculaceae (, buttercup or crowfoot family; Latin "little frog", from "frog") is a family (biology), family of over 2,000 known species of flowering plants in 43 genera, distributed worldwide. The largest genera are ''Ranunculus'' (600 spec ...
and others, need conditions cooler than -5 C. Some seeds will only germinate after hot temperatures during a
forest fire A wildfire, forest fire, or a bushfire is an unplanned and uncontrolled fire in an area of combustible vegetation. Depending on the type of vegetation present, a wildfire may be more specifically identified as a bushfire ( in Australia), dese ...
which cracks their seed coats; this is a type of physical dormancy. Most common annual
vegetable Vegetables are edible parts of plants that are consumed by humans or other animals as food. This original meaning is still commonly used, and is applied to plants collectively to refer to all edible plant matter, including edible flower, flo ...
s have optimal germination temperatures between 75–90 F (24–32 C), though many species (e.g.
radish The radish (''Raphanus sativus'') is a flowering plant in the mustard family, Brassicaceae. Its large taproot is commonly used as a root vegetable, although the entire plant is edible and its leaves are sometimes used as a leaf vegetable. Origina ...
es or
spinach Spinach (''Spinacia oleracea'') is a leafy green flowering plant native to Central Asia, Central and Western Asia. It is of the order Caryophyllales, family Amaranthaceae, subfamily Chenopodioideae. Its leaves are a common vegetable consumed eit ...
) can germinate at significantly lower temperatures, as low as 40 F (4 C), thus allowing them to be grown from seeds in cooler climates. Suboptimal temperatures lead to lower success rates and longer germination periods. * Light or darkness can be an environmental trigger for germination and is a type of physiological dormancy. Most seeds are not affected by light or darkness, but many photoblastic seeds, including species found in forest settings, will not germinate until an opening in the canopy allows sufficient light for the growth of the seedling. *
Scarification Scarification involves scratching, etching, burning/ branding, or superficially cutting designs, pictures, or words into the skin as a permanent body modification or body art. The body modification can take roughly 6–12 months to heal. In t ...
mimics natural processes that weaken the seed coat before germination. In nature, some seeds require particular conditions to germinate, such as the heat of a fire (e.g., many Australian native plants), or soaking in a body of water for a long period of time. Others need to be passed through an animal's
digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...
to weaken the seed coat enough to allow the seedling to emerge.


Dormancy

Some live seeds are dormant and need more time, and/or need to be subjected to specific environmental conditions before they will germinate.
Seed dormancy Seed dormancy is an evolutionary adaptation that prevents seeds from germinating during unsuitable ecological conditions that would typically lead to a low probability of seedling survival. Dormant seeds do not germinate in a specified period of ...
can originate in different parts of the seed, for example, within the embryo; in other cases the seed coat is involved. Dormancy breaking often involves changes in membranes, initiated by dormancy-breaking signals. This generally occurs only within hydrated seeds. Factors affecting seed dormancy include the presence of certain plant hormones, notably
abscisic acid Abscisic acid (ABA or abscisin II) is a plant hormone. ABA functions in many plant developmental processes, including seed and bud dormancy, the control of organ size and stomatal closure. It is especially important for plants in the response to ...
, which inhibits germination, and
gibberellin Gibberellins (GAs) are plant hormones that regulate various Biological process, developmental processes, including Plant stem, stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence. They are one of th ...
, which ends seed dormancy. In
brewing Brewing is the production of beer by steeping a starch source (commonly cereal grains, the most popular of which is barley) in water and #Fermenting, fermenting the resulting sweet liquid with Yeast#Beer, yeast. It may be done in a brewery ...
, barley seeds are treated with gibberellin to ensure uniform seed germination for the production of barley
malt Malt is any cereal grain that has been made to germinate by soaking in water and then stopped from germinating further by drying with hot air, a process known as "malting". Malted grain is used to make beer, whisky, malted milk, malt vinegar, ...
.


Seedling establishment

In some definitions, the appearance of the
radicle In botany, the radicle is the first part of a seedling (a growing plant embryo) to emerge from the seed during the process of germination. The radicle is the embryonic root of the plant, and grows downward in the soil (the shoot emerges from t ...
marks the end of germination and the beginning of "establishment", a period that utilizes the food reserves stored in the seed. Germination and establishment as an independent organism are critical phases in the life of a plant when they are the most vulnerable to injury, disease, and water stress. The germination index can be used as an indicator of
phytotoxicity Phytotoxicity describes any adverse effects on plant growth, physiology, or metabolism caused by a chemical substance, such as high levels of fertilizers, herbicides, heavy metals, or nanoparticles. General phytotoxic effects include altered plan ...
in soils. The mortality between dispersal of seeds and completion of the establishment can be so high that many species have adapted to produce large numbers of seeds.


Germination rate and germination capacity

In
agriculture Agriculture encompasses crop and livestock production, aquaculture, and forestry for food and non-food products. Agriculture was a key factor in the rise of sedentary human civilization, whereby farming of domesticated species created ...
and
gardening Gardening is the process of growing plants for their vegetables, fruits, flowers, herbs, and appearances within a designated space. Gardens fulfill a wide assortment of purposes, notably the production of Aesthetics, aesthetically pleasing area ...
, the germination rate describes how many seeds of a particular
plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...
, variety or seedlot are likely to germinate over a given period. It is a measure of germination time course and is usually expressed as a percentage, e.g., an 85% germination rate indicates that about 85 out of 100 seeds will probably germinate under proper conditions over the germination period given. Seed germination rate is determined by the seed genetic composition, morphological features and environmental factors. The germination rate is useful for calculating the number of seeds needed for a given area or desired number of plants. For seed physiologists and seed scientists "germination rate" is the reciprocal of time taken for the process of germination to complete starting from time of
sowing Sowing is the process of planting seeds. An area that has had seeds planted in it will be described as a sowed or sown area. Plants which are usually sown Among the major field crops, oats, wheat, and rye are sown, grasses and legumes are ...
. On the other hand, the number of seed able to complete germination in a population (i.e. seed lot) is referred to as germination capacity. Soil salinity is one of the stress factors that can limit the germination rate. Environmental stress activates some stress-related activities uZn-superoxide dismutase (SOD), Mn-SOD, L-ascorbate oxidase">superoxide_dismutase.html" ;"title="uZn-superoxide dismutase">uZn-superoxide dismutase (SOD), Mn-SOD, L-ascorbate oxidase (AO), DNA polymerase Delta 1 (POLD)-1, Chaperon (CHAPE) and heat shock protein (HSP)-21], genetic template stability and photosynthetic pigment activation. Application of exogenic glutamine limiting this process. Research carried out on
onion An onion (''Allium cepa'' , from Latin ), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus '' Allium''. The shallot is a botanical variety of the onion which was classifie ...
seeds shows a reduction in the mean germination time, an increase in the coefficient of germination velocity, the germination index and germination percentage after administration of exogenous glutamine to plants.


Repair of DNA damage

Seed quality deteriorates with age, and this is associated with accumulation of genome damage. During germination,
repair The technical meaning of maintenance involves functional checks, servicing, repairing or replacing of necessary devices, equipment, machinery, building infrastructure and supporting utilities in industrial, business, and residential installat ...
processes are activated to deal with accumulated
DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. A weakened capacity for DNA repair is a risk factor for the development of cancer. DNA is constantly modified ...
. In particular, single- and double-strand breaks in DNA can be repaired. The DNA damage checkpoint kinase ATM has a major role in integrating progression through germination with repair responses to the DNA damages accumulated by the aged seed.


Dicot germination

The part of the plant that first emerges from the seed is the embryonic root, termed the
radicle In botany, the radicle is the first part of a seedling (a growing plant embryo) to emerge from the seed during the process of germination. The radicle is the embryonic root of the plant, and grows downward in the soil (the shoot emerges from t ...
or primary root. It allows the seedling to become anchored in the ground and start absorbing water. After the root absorbs water, an embryonic
shoot Shoot most commonly refers to: * Shoot (botany), an immature plant or portion of a plant * Shooting, the firing of projectile weapons * Photo shoot, a photography session; an event wherein a photographer takes photographs Shoot may also refer t ...
, termed the plumule emerges from the seed. This shoot comprises three main parts: the
cotyledon A cotyledon ( ; ; "a cavity, small cup, any cup-shaped hollow", gen. (), ) is a "seed leaf" – a significant part of the embryo within the seed of a plant – and is formally defined as "the embryonic leaf in seed-bearing plants, one or mor ...
s (seed leaves), the section of shoot below the cotyledons (
hypocotyl The hypocotyl (short for "hypocotyledonous stem", meaning "below seed leaf") is the stem of a germinating seedling, found below the cotyledons (seed leaves) and above the radicle (root). Eudicots As the plant embryo grows at germination, it send ...
), and the section of shoot above the cotyledons (
epicotyl An epicotyl is important for the beginning stages of a plant's life. It is the region of a seedling stem above the stalks of the seed leaves of an embryo plant. It grows rapidly, showing hypogeal germination, and extends the stem above the soil su ...
). The way the shoot emerges differs among plant groups.


Epigeal

Epigeal germination Epigeal germination (Ancient Greek [] 'above ground', from [] 'on' and [] 'earth, ground') is a Glossary of botanical terms, botanical term indicating that the germination of a plant takes place above the ground. An example of a plant with epig ...
(or epigeous germination) is a botanical term indicating that the germination takes place above the ground. In epigeal germination, the ''hypocotyl'' elongates and forms a hook, pulling rather than pushing the
cotyledon A cotyledon ( ; ; "a cavity, small cup, any cup-shaped hollow", gen. (), ) is a "seed leaf" – a significant part of the embryo within the seed of a plant – and is formally defined as "the embryonic leaf in seed-bearing plants, one or mor ...
s and
apical meristem In cell biology, the meristem is a structure composed of specialized tissue found in plants, consisting of stem cells, known as meristematic cells, which are undifferentiated cells capable of continuous cellular division. These meristematic ce ...
through the soil. Once it reaches the surface, it straightens and pulls the cotyledons and shoot tip of the growing seedlings into the air.
Bean A bean is the seed of some plants in the legume family (Fabaceae) used as a vegetable for human consumption or animal feed. The seeds are often preserved through drying (a ''pulse''), but fresh beans are also sold. Dried beans are traditi ...
s, tamarind, and papaya are examples of plants that germinate this way.


Hypogeal

Germination can also be done by hypogeal germination (or hypogeous germination), where the epicotyl elongates and forms the hook. In this type of germination, the cotyledons stay underground where they eventually decompose. For example: peas,
chickpea The chickpea or chick pea (''Cicer arietinum'') is an annual plant, annual legume of the family (biology), family Fabaceae, subfamily Faboideae, cultivated for its edible seeds. Its different types are variously known as gram," Bengal gram, ga ...
s and mango germinate this way.


Monocot germination

In
monocot Monocotyledons (), commonly referred to as monocots, (Lilianae ''sensu'' Chase & Reveal) are flowering plants whose seeds contain only one Embryo#Plant embryos, embryonic leaf, or cotyledon. A monocot taxon has been in use for several decades, but ...
seeds, the embryo's radicle and cotyledon are covered by a coleorhiza and
coleoptile Coleoptile is the pointed protective sheath covering the emerging shoot in monocotyledons such as grasses in which few leaf primordia and shoot apex of monocot embryo remain enclosed. The coleoptile protects the first leaf as well as the growing ...
, respectively. The coleorhiza is the first part to grow out of the seed, followed by the radicle. The coleoptile is then pushed up through the ground until it reaches the surface. There, it stops elongating and the first leaves emerge.


Precocious germination

When a seed germinates without undergoing all four stages of seed development, i.e., globular, heart shape, torpedo shape, and cotyledonary stage, it is known as precocious germination.


Pollen germination

Another germination event during the life cycle of
gymnosperm The gymnosperms ( ; ) are a group of woody, perennial Seed plant, seed-producing plants, typically lacking the protective outer covering which surrounds the seeds in flowering plants, that include Pinophyta, conifers, cycads, Ginkgo, and gnetoph ...
s and
flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
s is the germination of a pollen grain after
pollination Pollination is the transfer of pollen from an anther of a plant to the stigma (botany), stigma of a plant, later enabling fertilisation and the production of seeds. Pollinating agents can be animals such as insects, for example bees, beetles or bu ...
. Like seeds,
pollen Pollen is a powdery substance produced by most types of flowers of seed plants for the purpose of sexual reproduction. It consists of pollen grains (highly reduced Gametophyte#Heterospory, microgametophytes), which produce male gametes (sperm ...
grains are severely dehydrated before being released to facilitate their dispersal from one plant to another. They consist of a protective coat containing several cells (up to 8 in gymnosperms, 2–3 in flowering plants). One of these cells is a tube cell. Once the pollen grain lands on the stigma of a receptive
flower Flowers, also known as blooms and blossoms, are the reproductive structures of flowering plants ( angiosperms). Typically, they are structured in four circular levels, called whorls, around the end of a stalk. These whorls include: calyx, m ...
(or a female
cone In geometry, a cone is a three-dimensional figure that tapers smoothly from a flat base (typically a circle) to a point not contained in the base, called the '' apex'' or '' vertex''. A cone is formed by a set of line segments, half-lines ...
in gymnosperms), it takes up water and germinates. Pollen germination is facilitated by
hydration Hydration may refer to: * Hydrate, a substance that contains water * Hydration enthalpy, energy released through hydrating a substance * Hydration reaction, a chemical addition reaction where a hydroxyl group and proton are added to a compound * H ...
on the stigma, as well as by the structure and
physiology Physiology (; ) is the science, scientific study of function (biology), functions and mechanism (biology), mechanisms in a life, living system. As a branches of science, subdiscipline of biology, physiology focuses on how organisms, organ syst ...
of the stigma and style. Pollen can also be induced to germinate ''in vitro'' (in a
petri dish A Petri dish (alternatively known as a Petri plate or cell-culture dish) is a shallow transparent lidded dish that biologists use to hold growth medium in which cells can be cultured,R. C. Dubey (2014): ''A Textbook Of Biotechnology For Class- ...
or test tube). During germination, the tube cell elongates into a
pollen tube A pollen tube is a tubular structure produced by the male gametophyte of seed plants when it germinates. Pollen tube elongation is an integral stage in the plant life cycle. The pollen tube acts as a conduit to transport the male gamete cells fr ...
. In the flower, the pollen tube then grows towards the
ovule In seed plants, the ovule is the structure that gives rise to and contains the female reproductive cells. It consists of three parts: the ''integument'', forming its outer layer, the ''nucellus'' (or remnant of the sporangium, megasporangium), ...
where it discharges the
sperm Sperm (: sperm or sperms) is the male reproductive Cell (biology), cell, or gamete, in anisogamous forms of sexual reproduction (forms in which there is a larger, female reproductive cell and a smaller, male one). Animals produce motile sperm ...
produced in the pollen grain for fertilization. The germinated pollen grain with its two sperm cells is the mature male microgametophyte of these plants.


Self-incompatibility

Since most plants carry both male and female reproductive organs in their flowers, there is a high risk of self-pollination and thus
inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely genetic distance, related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genet ...
. Some plants use the control of pollen germination as a way to prevent this self-pollination. Germination and growth of the pollen tube involve molecular signaling between stigma and pollen. In
self-incompatibility in plants Self-incompatibility (SI) is a general name for several genetic mechanisms that prevent self-fertilization in sexually reproducing organisms, and thus encourage outcrossing and allogamy. It is contrasted with separation of sexes among individual ...
, the stigma of certain plants can molecularly recognize pollen from the same plant and prevent it from germinating.


Spore germination

Germination can also refer to the emergence of cells from
resting spore A resting spore is a resistant cell, adapted to survive adverse environmental conditions. Resting spore is a term commonly applied to both diatoms and fungi. In fungi and oomycetes A resting spore can be a spore created by fungi which is thickly ...
s and the growth of
sporeling A sporeling is a young plant or fungus produced by a germinated spore, similar to a seedling derived from a germinated seed. They occur in algae, fungi, lichens, bryophytes and seedless vascular plants. Sporeling development Most spores germin ...
hypha A hypha (; ) is a long, branching, filamentous structure of a fungus, oomycete, or actinobacterium. In most fungi, hyphae are the main mode of vegetative growth, and are collectively called a mycelium. Structure A hypha consists of one o ...
e or
thalli Thallus (: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. A thallus usually names the entir ...
from spores in
fungi A fungus (: fungi , , , or ; or funguses) is any member of the group of eukaryotic organisms that includes microorganisms such as yeasts and mold (fungus), molds, as well as the more familiar mushrooms. These organisms are classified as one ...
,
alga Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...
e and some plants.
Conidia A conidium ( ; : conidia), sometimes termed an asexual chlamydospore or chlamydoconidium (: chlamydoconidia), is an asexual, non- motile spore of a fungus. The word ''conidium'' comes from the Ancient Greek word for dust, ('). They are also ...
are asexual reproductive (reproduction without the fusing of gametes) spores of fungi which germinate under specific conditions. A variety of cells can be formed from the germinating conidia. The most common are germ tubes which grow and develop into hyphae. The initial formation and subsequent elongation of the germ tube in the fungus ''Aspergillus niger'' has been captured in 3D using
holotomography Holotomography (HT) is a laser technique to measure the three-dimensional refractive index (RI) tomogram of a microscopic sample such as biological cells and tissues. Because the RI can serve as an intrinsic imaging contrast for transparent or pha ...
microscopy. Another type of cell is a conidial anastomosis tube (CAT); these differ from germ tubes in that they are thinner, shorter, lack branches, exhibit determinate growth and home toward each other. Each cell is of a tubular shape, but the conidial anastomosis tube forms a bridge that allows fusion between conidia.


Resting spores

In
resting spore A resting spore is a resistant cell, adapted to survive adverse environmental conditions. Resting spore is a term commonly applied to both diatoms and fungi. In fungi and oomycetes A resting spore can be a spore created by fungi which is thickly ...
s, germination involves cracking the thick cell wall of the dormant spore. For example, in
zygomycete Zygomycota, or zygote fungi, is a former division or phylum of the kingdom Fungi. The members are now part of two phyla: the Mucoromycota and Zoopagomycota. Approximately 1060 species are known. They are mostly terrestrial in habitat, living i ...
s the thick-walled zygosporangium cracks open and the
zygospore A zygospore is a diploid reproductive stage in the life cycle of many fungi and protists. Zygospores are created by the nuclear fusion of haploid cells. In fungi, zygospores are formed in zygosporangia after the fusion of specialized budding stru ...
inside gives rise to the emerging sporangiophore. In
slime molds Slime mold or slime mould is an informal name given to a polyphyly, polyphyletic assemblage of unrelated eukaryotic organisms in the Stramenopiles, Rhizaria, Discoba, Amoebozoa and Holomycota clades. Most are near-microscopic; those in the Myx ...
, germination refers to the emergence of
amoeboid An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and r ...
cells from the hardened spore. After cracking the spore coat, further development involves cell division, but not necessarily the development of a multicellular organism (for example in the free-living amoebas of slime molds).


Ferns and mosses

In
plant Plants are the eukaryotes that form the Kingdom (biology), kingdom Plantae; they are predominantly Photosynthesis, photosynthetic. This means that they obtain their energy from sunlight, using chloroplasts derived from endosymbiosis with c ...
s such as
bryophyte Bryophytes () are a group of embryophyte, land plants (embryophytes), sometimes treated as a taxonomic Division (taxonomy), division referred to as Bryophyta ''Sensu#Common qualifiers, sensu lato'', that contains three groups of non-vascular pla ...
s,
fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...
s, and a few others, spores germinate into independent
gametophyte A gametophyte () is one of the two alternating multicellular phases in the life cycles of plants and algae. It is a haploid multicellular organism that develops from a haploid spore that has one set of chromosomes. The gametophyte is the se ...
s. In the bryophytes (e.g.,
moss Mosses are small, non-vascular plant, non-vascular flowerless plants in the taxonomic phylum, division Bryophyta (, ) ''sensu stricto''. Bryophyta (''sensu lato'', Wilhelm Philippe Schimper, Schimp. 1879) may also refer to the parent group bryo ...
es and
liverworts Liverworts are a group of non-vascular plant, non-vascular embryophyte, land plants forming the division Marchantiophyta (). They may also be referred to as hepatics. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in wh ...
), spores germinate into
protonema A protonema (plural: protonemata) is a thread-like chain of cells that forms the earliest stage of development of the gametophyte (the haploid phase) in the life cycle of mosses. When a moss first grows from a spore, it starts as a ''germ tube'', ...
ta, similar to fungal hyphae, from which the gametophyte grows. In
fern The ferns (Polypodiopsida or Polypodiophyta) are a group of vascular plants (plants with xylem and phloem) that reproduce via spores and have neither seeds nor flowers. They differ from mosses by being vascular, i.e., having specialized tissue ...
s, the gametophytes are small, heart-shaped
prothalli A prothallus, or prothallium, (from Latin ''pro'' = forwards and Greek ''θαλλος'' (''thallos'') = twig) is usually the gametophyte stage in the life of a fern or other pteridophyte. Occasionally the term is also used to describe the young ...
that can often be found underneath a spore-shedding adult plant.


Bacteria

Bacterial spores can be exospores or
endospore An endospore is a dormant, tough, and non-reproductive structure produced by some bacteria in the phylum Bacillota. The name "endospore" is suggestive of a spore or seed-like form (''endo'' means 'within'), but it is not a true spore (i.e., not ...
s which are dormant structures produced by a number of different bacteria. They have no or very low metabolic activity and are formed in response to adverse environmental conditions. They allow survival and are not a form of reproduction. Under suitable conditions the spore germinates to produce a viable bacterium. Endospores are formed inside the mother cell, whereas exospores are formed at the end of the mother cell as a bud.


Light-stimulated germination

As mentioned earlier,
light Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
can be an environmental factor that stimulates the germination process. The seed needs to be able to determine when is the perfect time to germinate and they do that by sensing environmental cues. Once germination starts, the stored nutrients that have accumulated during maturation start to be digested which then supports cell expansion and overall growth. Within light-stimulated germination,
phytochrome Phytochromes are a class of photoreceptor proteins found in plants, bacteria and fungi. They respond to light in the red and far-red regions of the visible spectrum and can be classed as either Type I, which are activated by far-red light, or ...
B ( PHYB) is the photoreceptor that is responsible for the beginning stages of germination. When red light is present, PHYB is converted to its active form and moves from the cytoplasm to the nucleus where it upregulates the degradation of PIF1. PIF1, phytochrome-interaction-factor-1, negatively regulates germination by increasing the expression of proteins that repress the synthesis of
gibberellin Gibberellins (GAs) are plant hormones that regulate various Biological process, developmental processes, including Plant stem, stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence. They are one of th ...
(GA), a major hormone in the germination process. Another factor that promotes germination is HFR1 which accumulates in light in some way and forms inactive heterodimers with PIF1. Although the exact mechanism is not known,
nitric oxide Nitric oxide (nitrogen oxide, nitrogen monooxide, or nitrogen monoxide) is a colorless gas with the formula . It is one of the principal oxides of nitrogen. Nitric oxide is a free radical: it has an unpaired electron, which is sometimes den ...
(NO) plays a role in this pathway as well. NO is thought to repress PIF1 gene expression and stabilises HFR1 in some way to support the start of germination. Bethke et al. (2006) exposed dormant ''Arabidopsis'' seeds to NO gas and within the next 4 days, 90% of the seeds broke dormancy and germinated. The authors also looked at how NO and GA effects the vacuolation process of aleurone cells that allow the movement of nutrients to be digested. A NO mutant resulted in inhibition of vacuolation but when GA was later added the process was active again leading to the belief that NO is prior to GA in the pathway. NO may also lead to the decrease in sensitivity of
abscisic acid Abscisic acid (ABA or abscisin II) is a plant hormone. ABA functions in many plant developmental processes, including seed and bud dormancy, the control of organ size and stomatal closure. It is especially important for plants in the response to ...
(ABA), a plant hormone largely responsible for seed dormancy. The balance between GA and ABA is important. When ABA levels are higher than GA then that leads to dormant seeds and when GA levels are higher, seeds germinate. The switch between seed dormancy and germination needs to occur at a time when the seed has the best chances of surviving and an important cue that begins the process of seed germination and overall plant growth is light.


See also

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Lily seed germination types Lilies seed germination is classified as either epigeal or hypogeal. These classifications may be further refined as immediate or delayed. Whether a lily is epigeal or hypogeal may be related to survival strategies developed according to the cl ...
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Oldest viable seed There have been several seeds known at different times as the oldest viable seed. Dormancy allows seeds to survive for extended periods, which can aid in seed dispersal and spread out the growth and establishment of seedlings, increasing the ...
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Pot farm Container gardening or pot gardening/farming is the practice of growing plants, including edible plants, exclusively in containers instead of planting them in the ground. A container in gardening is a small, enclosed and usually portable object ...
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Pyrophyte Pyrophytes are plants which have adapted to tolerate fire. Fire acts favourably for some species. "Passive pyrophytes" resist the effects of fire, particularly when it passes over quickly, and hence can out-compete less resistant plants, which are ...
, for germination after fire *
Seed tray A tray is a shallow platform designed for the carrying of items. It can be fashioned from numerous materials, including silver, brass, sheet iron, paperboard, wood, melamine, and molded pulp. Trays range in cost from inexpensive molded pulp tray ...
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Seedling A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embry ...
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Sprouting Sprouting is the natural process by which seeds or spores germination, germinate and put out Shoot (botany), shoots, and already established plants produce new leaves or buds, or other Plant development#Adventitious structures, structures expe ...
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Urban horticulture Urban horticulture is the science and study of the growing plants in an urban environment. It focuses on the functional use of horticulture so as to maintain and improve the surrounding urban area. Urban horticulture has seen an increase in atten ...
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Vivipary In plants, vivipary occurs when seeds or embryos begin to develop before they detach from the parent. Plants such as some Iridaceae and Agavoideae grow cormlets in the axils of their inflorescences. These fall and in favourable circumstances t ...
, when seeds or embryos begin to develop inside or before they detach from the parent


References


Further reading

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External links


Sowing Seeds
a survey of seed sowing techniques
Germination time-lapse
≈1 minute HD video of mung bean seeds germinating over 10 days, on
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{{Authority control Seeds Plant physiology Articles containing video clips