The transfer of pollen from the anther to the stigma of the pistil is called pollination. There are two types of pollination: cross-pollination and self-pollination.
At self-pollination the stigma receives pollen from the same flower or another, but the same individual. Pollination is possible in closed, unblown flowers (peas). At cross Pollination transfers pollen from different individuals. This is the main type of pollination of flowering plants (apple, willow, cucumber, etc.).
cross pollination
Cross-pollination is carried out by natural (insects, birds, bats, wind, water) and artificial (man-produced) ways.
The adaptability of plants to wind pollination is manifested in the presence of bare flowers, or inconspicuous, poorly developed perianths. They are devoid of nectaries and smell, they form a lot of pollen, it is light, dry, small, the stigmas are long, with a large surface for trapping pollen (rye, corn).
The adaptability of plants to pollination by insects is characterized by the bright color of the corolla, the presence of nectaries, and the smell (dandelion, strawberry). Food for insects is nectar and pollen. The color and smell serve to attract pollinators. Sometimes the flowers have an odor characteristic of female insects of the same species. This attracts males to them, who carry out pollination. The evolution of flowering plants and their pollinators proceeded in parallel. This is the so-called coupled evolution.
Cross-pollination provides gene exchange, maintains high heterozygosity of populations, provides material for natural selection and preserves the most hardy offspring - carriers of the most favorable combination of genes.
artificial pollination
Artificial pollination is carried out by man to increase the yield or obtain new varieties of plants. At the same time, different methods are used to apply pollen to the stigma of the pistil. So, in corn that has same-sex flowers, pollen is collected by shaking the apical panicles of male flowers into paper funnels. Then the collected pollen is sprinkled with long stigmas of female flowers protruding at the top of the cob.
In artificial pollination of sunflowers, the stems of two neighboring plants are tilted so that the flowering surface of one basket can be pressed against the other. You can transfer pollen by alternately pressing your hand in a soft cloth mitten to the flowering baskets of different plants.
To obtain new varieties of plants with bisexual flowers, preparation for artificial pollination is necessary. First of all, anthers are removed from the flowers of the plant chosen as the mother, while still in bud, and these flowers are protected with gauze or paper bags from pollen. After 2-3 days, when the buds open, the harvested pollen of another variety is applied to the stigmas of the pistils with a clean, dry watercolor brush, soft foam rubber or a piece of rubber attached to the wire.
Double fertilization in flowering plants
After pollination, the process of fertilization takes place, but this requires a number of conditions: the pollen must not only stay on the stigma, but also grow through the style, reach the ovule and ensure the fusion of male cells with female ones.
Double fertilization is typical for flowering plants.
Usually, a lot of pollen grains fall on the stigma. They tend to have a rough surface and are held by the sticky skin of the stigma. In addition, when compatible pollen enters, stigma cells secrete substances that stimulate its germination.
Germination of pollen grains begins with swelling. Then, through special pores (channels) in the outer shell of the pollen grain, the inner one protrudes into a thin pollen tube, where the vegetative nucleus and spermine pass. The pollen tubes of all compatible grains held on the stigma of the pistil grow in a column, heading towards the ovule. One of them outstrips the others in growth and, having reached the pollen inlet, penetrates through it to the embryo sac and here pours its contents into it.
One of the sperm fuses with the egg, and the other with the secondary nucleus of the central diploid cell. The vegetative nucleus is destroyed even before the penetration of the pollen tube into the embryo sac.
Double fertilization in flowering plants was discovered by Russian cytologist and plant embryologist S.G. Navashin in 1898.
In the presence of ovules in the ovary, the above-described process of double fertilization occurs in each of them. It is called double because two male cells merge with two cells of the female gametophyte. Later, after fertilization, the development of the seed and fruit begins in the flower.
seed formation
After fertilization, a rapid mitotic division of the triploid secondary nucleus begins inside the embryo sac, which does not have a dormant period. A large number of nuclei are formed, then partitions appear between them.
These newly formed cells continue to divide, filling the entire cavity of the embryo sac with nutrient tissue - endosperm, which in some plants is completely consumed during the development of the embryo (legumes, pumpkins), while in others it is stored in mature seeds (cereals). At the same time, the embryo sac and the ovule grow.
The formation of the embryo begins with the division of the zygote. After a dormant period, the zygote divides mitotically into two cells. The upper cell, adjacent to the pollen passage, forms a pendant that pushes the lower cell deeper into the endosperm. The suspension in some plant species remains unicellular, in others it is divided by transverse partitions and becomes multicellular. The lower cell grows into a pre-embryo of a spherical seed. The pre-embryo is divided into 4 cells by two perpendicular partitions, then each of these cells is divided into two more.
At first, the cells are more or less homogeneous. With further division, the cells differentiate into a rudimentary root, a rudimentary stem, rudimentary leaflets (cotyledons) and a rudimentary bud surrounded by cotyledons. By this time, the ovule turns into a seed, its integument and the remnants of the endosperm form the seed skin.
Thus, a seed embryo is formed from a fertilized diploid egg, and a nutritional tissue - endosperm - from a secondary triploid cell, the integuments of the ovule turn into integuments of the seed, and the wall of the ovary, growing, forms the pericarp.
double fertilization the sexual process in angiosperms, in which both the egg and the central cell of the embryo sac are fertilized (See Embryo sac). Before. discovered by the Russian scientist S. G. Navashin in 1898 on 2 plant species - lilies (Lilium martagon) and hazel grouse (Fritillaria orientalis). In D. about. both sperm are involved, brought into the embryo sac by the pollen tube; the nucleus of one sperm (See sperm) merges with the nucleus of the egg, the nucleus of the second - with the polar nuclei or with the secondary nucleus of the embryo sac. A fertilized egg develops into an embryo ,
from the central cell - Endosperm. In embryo sacs with a three-celled egg apparatus, the contents of the pollen tube usually pour into one of the synergids (See Synergids) ,
which is destroyed in this case (there are visible remains of the nucleus of the synergy and the vegetative nucleus of the pollen tube); the second synergid subsequently dies off. Further, both spermatozoa, together with the altered cytoplasm of the pollen tube, move into the slit-like gap between the egg and the central cell. Then the sperm dissociate: one of them penetrates the egg and comes into contact with its nucleus, the other penetrates into the central cell, where it contacts the secondary nucleus or one, and sometimes both, polar nuclei. Sperm lose their cytoplasm while still in the pollen tube or when they penetrate the embryo sac; sometimes sperm in the form of unchanged cells are also observed in the embryo sac. At D. about. nuclei of the embryo sac are in interphase (See Interphase) and are usually much larger than sperm nuclei, the shape and condition of which can vary. In skerda and some other Compositae, the sperm nuclei have the form of a double twisted or twisted chromatin filament; in many plants they are elongated, sometimes twisted, more or less chromatized, and do not have nucleoli; usually spermatozoa are rounded interphase nuclei with nucleoli, sometimes not differing in structure from female nuclei. According to the nature of the association of male and female nuclei, it was proposed (E. N. Gerasimova-Navashina) to distinguish two types of D. o .: premitotic - the sperm nucleus is immersed in the female nucleus, its chromosomes are despiralized; the unification of the chromosome sets of both nuclei occurs in the interphase (in the zygote); postmitotic - male and female nuclei, retaining their shells, enter prophase (See Prophase) ,
at the end of which their unification begins; interphase nuclei containing chromosome sets of both nuclei are formed only after the first mitotic division of the zygote. At D. about. 2 haploid nuclei fuse in the egg, so the nucleus of the zygote is diploid. The number of chromosomes in the nuclei of the endosperm depends on the number of polar nuclei in the central cell and on their ploidy (See Ploidy) ;
Most angiosperms have 2 haploid polar nuclei and their endosperm is triploid. Consequence D. o. - Xenia -
manifestation of dominant traits of the endosperm of the paternal plant in the endosperm of hybrid seeds. If several pollen tubes penetrate the embryo sac, the sperm of the first of them participate in D. o., the sperm of the rest degenerate. Cases of dyspermia, i.e. fertilization of the egg by two sperm, are very rare. Lit.: Navashin S. G., Izbr. works, vol. 1, M.-L., 1951; Mageshwar and P., Angiosperm Embryology, trans. from English, M., 1954; Poddubnaya Arnoldi V. A., General embryology of angiosperms, M., 1964; Steffen, K., Fertilisation, in: Maheshwari P. (ed.). Recent advances in the embryology of angiosperms, Delhi, 1963. I. D. Romanov.
Great Soviet Encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what "Double fertilization" is in other dictionaries:
Only characteristic of flowering plants. In double fertilization, one of the sperm fuses with the egg, and the second with the central cell of the embryo sac. An embryo develops from a fertilized egg, a secondary one develops from a central cell ... ... Big Encyclopedic Dictionary
A type of sexual process peculiar only to flowering plants. Discovered in 1898 by S. G. Navashin in lilies. Before. lies in the fact that during the formation of the seed, not only the egg is fertilized, but also the center, the nucleus of the embryonic sac. From the zygote ... ...
double fertilization- The type of sexual process characteristic of flowering plants: one of the sperm fertilizes the egg, and the other (from the same pollen tube) fertilizes the central nucleus of the embryo sac, as a result of the first process, a diploid is formed ... ... Technical Translator's Handbook
Only characteristic of flowering plants. In double fertilization, one of the sperm fuses with the egg, and the second with the central cell of the embryo sac. An embryo develops from a fertilized ovum, a secondary one develops from a central cell ... ... encyclopedic Dictionary
Double fertilization The type of sexual process characteristic of flowering plants: one of the sperm fertilizes the egg, and the other (from the same pollen tube
It is peculiar only to flowering rows. At D. about. one of the sperm merges with the egg, and the second with the center. embryo sac cell. From a fertilized egg, an embryo develops from the center. cells are the secondary endosperm of the seed, containing ... ... Natural science. encyclopedic Dictionary
double fertilization- the process of fertilization that occurs in angiosperms, in which both sperm are formed. One of them merges with the egg, the second - with the central diploid cell of the embryo sac. Opened by S. G. Navashin in ... ... Plant anatomy and morphology
DOUBLE FERTILIZATION- the sexual process in angiosperms, which consists in the fusion of one male gamete of the pollen tube (sperm) with the egg of the embryo sac, and the second male gamete with the secondary nucleus of the embryo sac ... Glossary of botanical terms
double fertilization by navashin- PLANT EMBRYOLOGY DOUBLE FERTILIZATION ACCORDING TO NAVASHIN - the fusion of the egg and sperm to form a zygote (2p) and the simultaneous fusion of another sperm and a double nucleus to form the primary endosperm nucleus (3p). A common feature of all… General Embryology: Terminological Dictionary
Syngamy, the fusion of a male reproductive cell (sperm, sperm) with a female (egg, egg), leading to the formation of a zygote, the edge gives rise to a new organism. Animal O. is preceded by insemination. In the process of O., eggs are activated, ... ... Biological encyclopedic dictionary
The time interval between pollination and fertilization is usually very short in most angiosperms.
The pollen grain transferred on the stigma of the pistil in one way or another, germinating, forms a pollen tube that grows inside the style. Having reached the ovule, it penetrates the embryo sac through the pollen inlet.
The growing pollen tube from the pollen grain includes the nucleus of the siphonogenic cell and the spermatic cell. The sperm cell divides to form two sperm cells. Having penetrated into the embryo sac, the pollen tube pours out its contents near the egg apparatus, most often into the synergide, which is destroyed in the process. Another synergy persists for some time. One of the sperm combines with the egg, forming a zygote, the second goes to the secondary nucleus of the embryo sac and merges with it, forming a triploid nucleus.
Features of the behavior of sperm cells inside the embryo sac were first described by S.G. Navashin in 1898. He called this process double fertilization.
The division of the diploid nucleus of the zygote and the triploid nucleus of the central cell begin either a few hours after fertilization, or several days, weeks, or even months later. After fertilization, the embryo sac expands. This is facilitated by the influx of nutrients from the nucellus and integuments. Along with this, the size of the ovule also increases. A plant embryo develops from a fertilized egg, and a triploid nucleus gives rise to endosperm - reserve tissue.
However, in some plants, the nucellus is preserved in the mature seed, turning into a storage tissue - the perisperm, which lies under the seed coat.
5. The structure of the seed and fruit is also more developed.
The mature seed consists of:
1. germ,
2. storage tissues (endosperm and perisperm),
3. seed coat.
The differentiated embryo has the rudiments of all the vegetative organs of the future plant: the germinal root, the hypocotyl of the cotyledon.
Dicotyledonous plants usually have two cotyledons. Monocots have one cotyledon. In dicots, the cone of growth of the shoot is located between two cotyledons, in monocots it is shifted to the side.
Morphological types of seeds.
Types of seeds depending on the development of storage tissues:
1. Seeds with endosperm (wheat, corn).
2. Seeds without endosperm (peas, beans, pumpkin, sunflower). Nutrient reserves are concentrated in the cotyledons of the embryos.
3. Seeds with endosperm and perisperm (water lily, pod, black pepper).
4. Seeds with perisperm (cloves, quinoa, spinach).
Thus, reserve nutrients in seeds can be either outside the embryo, in special storage tissues (endosperm and perisperm), or in the embryo itself (in its cotyledons). The vast majority of flowering plants have endosperm in the mature seed.
Favorable conditions are necessary for seeds to germinate. humidity, aeration and temperature. The temperature at which seed germination occurs is lower in northern plants than in southern ones, especially tropical species. Wheat seeds, for example, can germinate at 0 ... + 1 0 C, meanwhile, for the germination of corn seeds, a temperature of at least + 12 ° C is required. The minimum temperature required for the germination of melon seeds and especially the seeds of many tropical plants, such as palm trees, is +20 and even + 25 ° С.
Seed germination is preceded by its swelling - a process associated with the absorption of a large amount of water and watering of the seed tissues.
As a result of enhanced nutrition, all organs of the embryo begin to grow. The germinal root usually breaks through the skin and protrudes out of the micropylar opening, giving rise to the main root. Following him, the apical bud starts to grow, forming the main shoot of the plant. Thus, the embryo turns into a seedling, the development of which lasts until the appearance of the first middle leaf.
The structure of the fetus.
The fruit is the reproductive organ of angiosperms that provides seed reproduction. The fruit develops from the flower (from the ovary of the pistil), after fertilization. From the wall of the ovary of the pistil, a pericarp is formed - the pericarp, which consists of three layers. exocarp, mesocarp, endocarp.
If only the ovary of the pistil took part in the formation of the fetus, then it is called real fruit. So, for example, in cherries, plums, tomatoes, the fruits will be real, because they are formed only from the ovary of the pestle.
In some plants, in addition to the pistil, the receptacle (cucumber, pumpkin) or the receptacle and flower tube (apple, pear) take part in the formation of the fruit. Such fruits are called false fruits. Thus, false called fruits, in the formation of which not only the ovary of the pistil takes part, but also other parts of the flower (receptacle, flower tube, calyx).
In some plants, the fruit develops not from one flower, but from several flowers, one way or another fused together. Fruits formed from the pistils of several flowers, and sometimes the whole inflorescence, are called infructescence. Fruiting is formed in mulberry, fig, pineapple, beet. Consider the structure of these infructescences. Beet seedlings are called glomeruli. The hard part of the glomerulus is the overgrown lignified pericarp of several flowers, seeds are placed inside them.
The structure of the fetus is closely related to the structure of the gynoecium. From the gynoecium, characterized by one pistil in the flower, a simple fruit. Simple fruits include drupe (cherry), bean (pea), caryopsis (wheat), etc.
From a gynoecium characterized by several non-fused pistils in a flower, a difficult or prefabricated fruit. Complex fruits include a combined achene or polyseed (cinquefoil, buttercup), a combined nut or a multi-nut (adonis, strawberry), a combined leaflet (catchment, peony), a combined drupe (raspberry, blackberry).
According to the structure of the pericarp, all fruits are divided into juicy and dry. The mesocarp is well developed in the succulents. In dry fruits, the mesocarp is not developed. They are single-seeded (contain one seed) and multi-seeded (contain many seeds).
Fruit classification
There are several classifications of fruits based on morphogenetic and evolutionary traits. In general, they are quite complex and difficult to apply. Therefore, let us consider an artificial classification of fruits, based mainly on the signs of external morphology.
I. Simple, dry, one-seeded, nut-like fruits.
All of these fruits are indehiscent.
Zernovka- this is a fruit in which the leathery pericarp fuses with the seed peel (rye, wheat, corn).
Achene- this is a fruit that has a leathery pericarp that does not grow together with the seed peel (sunflower, cornflower, aster).
Lionfish- a fruit with a leathery pericarp growing into winged appendages (elm, birch).
Nut- a fruit with a hard woody pericarp (hazel).
Acorn- this is a fruit with a less rigid pericarp than that of a nut and has a lignified cup-shaped plush (oak, beech).
Draw these fruits in your notebook, write down their definitions and give examples of plants in which they are formed.
II. Simple, dry, many-seeded, box-shaped fruits.
These are fruits that open when ripe.
Leaflet- a single-celled fruit, formed from one carpel, is opened along one seam (field larkspur).
Bean- a single-celled fruit, formed from one carpel, is opened along two seams (peas, beans, soybeans).
Pod- a bilocular fruit, formed from two carpels. Seeds are not attached to the valves (as in a bean), but to a membranous partition. It opens with two seams. The length of the pod is more than 4 times the width (cabbage, mustard).
Pod- a fruit that differs from the pod in that its length is equal to the width or exceeds it by no more than three times (yarutka, shepherd's purse).
box- This is a single-celled or multi-celled fruit, formed by several carpels. We open it in a variety of ways: with a lid - for henbane, with cloves - for cloves, cracking along the wings - for cotton, dope.
In some plant species, multi-seeded dry fruits can break up into separate single-seeded segments. Such fruits are called fractional. An example is a fractional nut or a four-nutlet - in plants of the labial family, borage, a fractional lionfish in a maple, a fractional pod in a radish, a fractional bean in a kopeck.
III. Simple, juicy fruits.
drupes- a single-shift fruit, in which the exocarp is thin, the mesocarp is composed, and the endocarp is hard, woody. The drupe fruit is formed in cherries, plums, apricots, peaches, cherries.
Berry- a multi-seeded fruit, in which the mesocarp and endocarp are juicy, and the exocarp is leathery (grapes, currants, tomatoes, potatoes, nightshade).
pumpkin- a false fruit formed from the lower ovary of the pistil. Mesocarp and endocarp are succulent. Exocarp hard, sometimes woody (pumpkin, cucumber, melon).
Apple- a false fruit formed from the lower ovary of the pistil. The pulp of the fruit consists of an overgrown receptacle and exocarp and mesocarp, cartilaginous, parchment or woody endocarp (apple, pear, quince, mountain ash, hawthorn).
Pomeranian or hesperidium- a fruit whose exocarp is thick, rich in essential oils, brightly colored. The mesocarp is a loose, white, tasteless tissue. The endocarp is juicy and consists of hairs rich in cell sap (tangerine, orange, grapefruit, lemon, etc.).
Similar information.
Fertilization- this is the process of fusion of male and female germ cells with the formation of a zygote. In plants, it can occur in water (in higher spore plants) and without water (in higher seed plants). In flowering plants, two sperm are involved in this process, so fertilization will be double. double fertilization- this is the process of fusion of two sperm with two different cells: one sperm merges with the egg, and the second with the central cell. This type of fertilization is characteristic only of flowering plants. The Ukrainian scientist S. G. Navashin discovered double fertilization in 1898.
In the ovary of the pistil, on the seed stalk, there is a seed germ, in which the integument and the central part, the nucelus, are isolated. At the apex there is a narrow channel - the pollen entrance, which leads to the embryo sac. And it is through this hole in most flowering plants that the pollen tube grows into the seed germ. Upon reaching the egg, the tip of the pollen tube breaks, two spermatozoa emerge from it, and the vegetative cell is destroyed. One of the sperm fuses with the egg to form a zygote, and the second with the central cell, from which the endosperm with a supply of nutrients will be formed. Thus, two spermatozoa fuse with two cells of the embryo sac, which is why fertilization in flowering plants is called "double fertilization". From the moment a speck of dust on the stigma of the pistil enters the process of double fertilization in different plants, it takes from 20-30 minutes to several days. So, in the seed germ, as a result of double fertilization in flowering plants, a zygote and a fertilized central cell are formed.
Pollination, double fertilization, seed formation and seedling formation in a flowering plant: A - flower. B - PILYAK with pollen grains. IN - pollen grain: 1 - vegetative cell; 2 - spermatozoa. G - pollen tube. D - pistil. E - seed germ. G - embryo sac 4 - egg; 5 - central cell. C - seed: 6 - seed coat; 7 - endosperm; 8 - embryo. And a sprout.
After fertilization, the fertilized central cell is the first to divide, which gives rise to a special tissue of the future seed - endosperm . The cells of this tissue fill the embryo sac and accumulate nutrients that are useful for the development of the seed embryo (in cereals). In other plants (in beans, pumpkins), nutrients can be deposited in the cells of the first leaflets of the embryo, which are called cotyledons. After the accumulation of a certain part of the nutrients in the endosperm, a fertilized egg begins its development - the zygote. This cell divides many times and gradually forms a multicellular seed germ , which gives rise to a new plant. The formed embryo contains an embryonic bud, germinal leaves - cotyledons, a rudimentary stem and a rudimentary root. From the integument of the seed germ is formed testa , which protects the fetus. So, after fertilization, a seed is formed from the seed germ, which consists of the seed coat, the seed embryo and the supply of nutrients.
In wheat blueberry more than a hundred ducks, -
in wheat blueberry hidden spikelet.
Babaeva Ksenia
DOUBLE FERTILIZATION IN FLOWERING PLANTS
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DOUBLE FERTILIZATION IN FLOWERING PLANTS
(1 slide) This process is characteristic of all angiosperms. The significance of double fertilization lies in the fact that the active development of nutritional tissue is ensured after fertilization. Therefore, the ovule in angiosperms does not store nutrients for the future and, consequently, develops much faster than in many other plants, such as gymnosperms.
The phenomenon was discovered by the Russian scientist S. G. Navashin in 1898 on 2 plant species - lilies (Lilium martagon) and hazel grouse (Fritillaria orientalis)
(2 slide) Gametes of flowering plants are formed in the main parts of the flower - stamens and pistils.
Slides captions:
Double fertilization - Characteristic for all angiosperms. It consists in the fact that the active development of nutrient tissue is ensured after fertilization.
Main parts of a flower:
Pollen is formed in the anthers Pollen forms the male sex cells
The female sex cells (ovules) are produced in the ovules in the ovary of the pistil.
The biological meaning of double fertilization is very large: Unlike gymnosperms, triploid endosperm is formed only in case of fertilization Considering the gigantic number of generations, this achieves significant energy savings.