Double fertilization, a sexual process in angiosperms in which both the egg and the central cell of the embryo sac are fertilized. Double fertilization was discovered by the Russian scientist S. G. Navashin in 1898 on 2 types of plants - lilies ( Lilium martagon) and hazel grouse ( Fritillaria orientalis). Double fertilization involves both sperm, brought into the embryo sac by the pollen tube; the nucleus of one sperm fuses with the nucleus of the egg, the nucleus of the second fuses with the polar nuclei or with the secondary nucleus of the embryo sac. The embryo develops from the fertilized egg, and the endosperm develops from the central cell. In embryo sacs with a three-celled egg apparatus, the contents of the pollen tube are usually poured into one of the synergids, which is destroyed (the remains of the synergid nucleus and the vegetative nucleus of the pollen tube are visible in it); the second synergid subsequently dies off. Next, both sperm, together with the modified cytoplasm of the pollen tube, move into the slit-like gap between the egg and the central cell. Then the sperm separate: one of them penetrates the egg and comes into contact with its nucleus, the other penetrates 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 upon penetration into the embryo sac; sometimes sperm in the form of unchanged cells are observed in the embryo sac.
During double fertilization, the nuclei of the embryo sac are in interphase and are usually much larger than the nuclei of sperm, the shape and condition of which can vary. In skerda and some other Asteraceae, the sperm nuclei have the appearance of a double twisted or crimped chromatin thread; in many plants they are elongated, sometimes crimped, more or less chromatized, and do not have nucleoli; usually sperm are round interphase nuclei with nucleoli, sometimes not different in structure from female nuclei.
Based on the nature of the union of male and female nuclei, it was proposed (E. N. Gerasimova-Navashina) to distinguish between two types of double fertilization: premitotic - the sperm nucleus is immersed in the female nucleus, its chromosomes are despiralized; the union of the chromosome sets of both nuclei occurs in interphase (in the zygote); postmitotic - the male and female nuclei, retaining their shells, enter 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. During double fertilization, 2 haploid nuclei fuse in the egg, so the zygote nucleus is diploid. The number of chromosomes in the endosperm nuclei depends on the number of polar nuclei in the central cell and on their ploidy; Most angiosperms have 2 haploid polar nuclei and their endosperm is triploid. The consequence of double fertilization - xenia - is the manifestation of dominant characteristics 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 one participates in double fertilization, while the sperm of the others degenerate. Cases of dispermia, i.e. fertilization of an egg by two sperm, are very rare.
Fertilization in angiosperms is preceded by micro- and megasporogenesis, and pollination.
Microsporogenesis occurs in the anthers of the stamens. In this case, the diploid cells of the educational tissue of the anther as a result of meiosis turn into 4 haploid microspores. Over time microspore begins mitotic division and transforms into male gametophyte – pollen grain.
Pollen grain the outside is covered with two shells: exine and intina. Exine– the upper shell is thicker and saturated with sporolennin, a fat-like substance. This allows the pollen to withstand significant temperature and chemical influences. The exine contains germinal pores, which are closed by “plugs” until pollination. Intina contains cellulose and is elastic. There are two cells in a pollen grain: vegetative and generative.
Megasporogenesis carried out in ovule. From the mother nucellus cells As a result of meiosis, 4 megaspores are formed, of which only one remains. This megaspore grows strongly and pushes the nucellus tissues towards the integuments, forming embryo sac. The nucleus of the embryo sac divides 3 times by mitosis. After the first division, the two daughter nuclei move to different poles: chalazal and micropylar, and there they are divided twice. Thus, there are four nuclei at each pole. Three nuclei at each pole are isolated into separate cells, and the remaining two move to the center and merge, forming a secondary diploid nucleus. On micropylar pole there are two synergids and one larger cell - egg. At the chalazal pole there are antipodes. Thus, a mature embryo sac contains 7 cells.
Pollination involves the transfer of pollen from the stamens to the stigma.
Fertilization. Pollen grains that somehow land on the stigma germinate. Pollen germination begins with the swelling of the grain and the formation of a pollen tube from the vegetative cell. The pollen tube breaks through the shell in its thinner place - the so-called aperture. The tip of the pollen tube secretes special substances that soften the tissues of the stigma and style. As the pollen tube grows, the nucleus of the vegetative cell and the generative cell pass into it, which divides and forms two sperm. Through the micropyle of the ovule, the pollen tube penetrates into the embryo sac, where it ruptures and its contents are poured inside. One of the sperm fuses with the egg to form a zygote, which then gives rise to the embryo of the seed. The second sperm fuses with the central nucleus, resulting in the formation of a triploid nucleus, which then develops into a triploid endosperm. Thus, endosperm in angiosperms triploid and secondary, because formed after fertilization.
This whole process is called double fertilization. It was first described by the Russian scientist S.G. Navashin. (1898).
Antipodes and synergids dissolve after fertilization, and integuments are converted into the seed coat.
Apomixis– development of an embryo from an unfertilized cell. The forms of apomixis depend on which parts of the ovule the embryo develops from. At parthenogenesis(parthenos-virgin) embryo arises from an unfertilized egg. If the embryo develops from any other cell of the gametophyte (antipodes, synergids), then this process is called apogamy. In the case of the formation of an embryo from nucellus cells, integuments not included in the gametophyte, we speak of aposporia. Apomixis is common among evolutionarily developed groups of plants. Due to apomixis, plants do not depend on pollinating agents.
/>DOUBLE FERTILIZATION sexual process in angiosperms, during which both the egg and the center are fertilized. cell embryo sac. Before. opened by Russian scientist S.G. Navashin in 1898 on 2 plant species - lily (Lilium martagon) and hazel grouse (Fritillaria orientalis ) . In D. o. both sperm are involved, brought into the embryo sac by the pollen tube; core of one sperm fuses with the nucleus of the egg , the nucleus of the second - with polar nuclei or with the secondary nucleus of the embryo sac. Develops from a fertilized egg embryo, from the center cells - endosperm. In embryo sacs with a three-cell facial apparatus, the contents of the pollen tube are usually poured into one of the synergide, which is destroyed (the remains of the synergida nucleus and the vegetative nucleus of the pollen tube are visible in it ) ; the second synergid subsequently dies off. Next, both sperm, together with the modified cytoplasm of the pollen tube, move into the slit-like gap between the egg and the center. cell. Then the sperm are separated: 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. Spermine lose their cytoplasm even in the pollen tube or upon penetration into the embryo sac; sometimes sperm in the form of unchanged cells are observed in
/>
embryo sac.
Double fertilization; 1 - in hazel grouse: one of the sperm (a) is in contact with the nucleus of the egg, the second (b) - with one of the polar nuclei (the second polar nucleus is not shown); 2 - y sunflower; A - pollen tube; 6 - synergids (one of them is damaged by the pollen tube); c - egg; d - sperm in contact with the nucleus of the egg; d - central cell; e- the second sperm is in contact with the secondary nucleus of the embryo sac.
With D. o. the nuclei of the embryo sac are located in interphase and usually much larger than sperm nuclei, the shape and condition of which can vary. In Skerda and some other Asteraceae, the sperm nuclei have the appearance of a double twisted or crimped chromatin thread; in many others. plants they are elongated, sometimes convoluted, b. or m. chromatized, without nucleoli; usually sperm are round interphase nuclei with nucleoli, sometimes not different in structure from female nuclei.
Based on the nature of the unification of male and female nuclei, it was proposed (E. N. Gerasimova-Navashina) to distinguish between two types of D. o.: premitotic - the sperm nucleus is immersed in the female nucleus, its chromosomes are despiralized; the union of the chromosome sets of both nuclei occurs in interphase (in the zygote ) ; postmitotic - male and female nuclei, retaining their shells, enter into prophase, at the end of the cut their unification begins; interphase nuclei, containing chromosome sets of both nuclei, are formed only after the first mitotic division of the zygote. With D. o. In the egg, 2 haploid nuclei fuse, so the zygote nucleus is diploid. The number of chromosomes in the endosperm nuclei depends on the number of polar nuclei in the center. cage and from them ploidy; Most angiosperms have 2 haploid polar nuclei and their endosperm is triploid. Consequence D. o. - Ksenia - manifestation of dominant traits of the endosperm of the paternal plant in the endosperm of hybrid seeds. If several penetrates into the embryo sac. pollen tubes, the sperm of the first of them participate in D. o., the sperm of the others degenerate. Cases of dispermia, i.e. fertilization of an egg by two sperm, are very rare.
Through a series of precise embryological studies on various representatives of angiosperms (lily, ranunculaceae, asteraceae), S. G. Navashin convincingly showed that the endosperm, like the embryo, is a product of the sexual process. He called this unusual phenomenon, characteristic only of angiosperms, double fertilization. He reported his discovery in August 1898 at the X Congress of Russian Naturalists and Doctors held in Kyiv, and in November of the same year he published a short article on this topic in the Izvestia of the St. Petersburg Academy of Sciences.
The idea of the existence of double fertilization arose from S. G. Navashin back in 1895 while working on the study of chalazogamy in the walnut. This idea received final confirmation and formalization into a coherent theory during the study of fertilization in lilies.
Later, S.G. Navashin described double fertilization in other flowering plants that were systematically far apart from each other - in representatives of the Ranunculaceae, Asteraceae, and Nutaceae, thereby proving the generality of this phenomenon for all angiosperms.
Double fertilization - hallmark, separating angiosperms from gymnosperms.
S. G. Navashin’s discovery of double fertilization in angiosperms played a role important role in science.
The phenomenon of double fertilization clarified not only the question of the origin of endosperm, but also clarified the mystery of such a phenomenon as xenia in corn. Navashin's work on the fertilization of angiosperms was greeted with great interest by botanists around the world.
Discussions about the essence of double fertilization continued at the beginning of the twentieth century. During these discussions, and most importantly, thanks to new research, Navashin’s conclusions were fully confirmed and further developed.
a sexual process in angiosperms in which both the egg and the central cell of the embryo sac are fertilized. Before. discovered by the Russian scientist S.
G. Navashin in 1898 on 2 plant species - lily (Lilium martagon) and hazel grouse (Fritillaria orientalis). In D. o. both sperm are involved, brought into the embryo sac by the pollen tube; the nucleus of one sperm fuses with the nucleus of the egg, the nucleus of the second fuses with the polar nuclei or with the secondary nucleus of the embryo sac. The embryo develops from the fertilized egg, and the endosperm develops from the central cell. In embryo sacs with a three-celled egg apparatus, the contents of the pollen tube are usually poured into one of the synergids, which is destroyed (the remains of the synergid nucleus and the vegetative nucleus of the pollen tube are visible in it); the second synergid subsequently dies off. Next, both sperm, together with the modified cytoplasm of the pollen tube, move into the slit-like gap between the egg and the central cell. Then the sperm separate: one of them penetrates the egg and comes into contact with its nucleus, the other penetrates 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 upon penetration into the embryo sac; sometimes sperm in the form of unchanged cells are observed in the embryo sac.
With D. o. The nuclei of the embryo sac are in interphase and are usually much larger than the nuclei of sperm cells, the shape and condition of which can vary. In skerda and some other Asteraceae, the sperm nuclei have the appearance of a double twisted or crimped chromatin thread; in many plants they are elongated, sometimes crimped, more or less chromatized, and do not have nucleoli; usually sperm are round interphase nuclei with nucleoli, sometimes not different in structure from female nuclei.
Based on the nature of the unification of male and female nuclei, it was proposed (E. N. Gerasimova-Navashina) to distinguish between two types of D. o.: premitotic - the sperm nucleus is immersed in the female nucleus, its chromosomes are despiralized; the union of the chromosome sets of both nuclei occurs in interphase (in the zygote); postmitotic ≈ male and female nuclei, retaining their shells, enter 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. With D. o. In the egg, 2 haploid nuclei fuse, so the zygote nucleus is diploid. The number of chromosomes in the endosperm nuclei depends on the number of polar nuclei in the central cell and on their 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 into the embryo sac, the sperm of the first one participates in pollen formation, while the sperm of the others degenerate. Cases of dispermia, i.e. fertilization of an egg by two sperm, are very rare.
Lit.: Navashin S. G., Izbr. works, vol. 1, M.≈L., 1951; Mageshwar and P., Embryology of Angiosperms, 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.
Double fertilization
Lecture Pollination
Pollination and fertilization must occur for an embryo to form.
Pollination- the process of transferring pollen from the stamen to the stigma. Pollination first appears in gymnosperms, but reaches its greatest perfection in angiosperms.
There are two types of pollination: self-pollination and cross-pollination. At self-pollination pollen from the same plant falls on the pistil of a flower; if pollen transfer occurs between flowers of different individuals, then cross pollination.
It is believed that it is characteristic of 90% of plants. Cross pollination causes high level heterozygosity of populations. This creates great opportunities for natural selection. Strict self-pollination is relatively rare (for example, in peas) and can lead to the splitting of the species into a number of pure lines, i.e. makes populations homozygous.
For the evolutionary process, a combination of self-pollination and cross-pollination is considered optimal, which often occurs in nature. One of the forms limiting self-pollination is dioecy, i.e. On some plants, only male (staminate) flowers develop, while on others, female (pistillate) flowers develop, having only gynoecium. Monoecious plants have flowers containing both androecium and gynoecium. Another form limiting self-pollination is complete physiological incompatibility. It is expressed in the suppression of pollen germination on the stigma of the same individual during self-pollination.
There are two types of cross-pollination: biotic and abiotic. Biotic Pollination is carried out by animals. Entomophily- pollination by insects; ornithophily- pollination by birds (hummingbirds). Abiotic pollination occurs with the help of non-living factors external environment: by the wind - anemophilia; water from aquatic plants — hydrophilia.
Double fertilization
The pollen, once on the stigma of the pistil, begins to germinate. A pollen tube is formed from the vegetative cell, and two sperm are formed from the generative cell. The pollen tube penetrates the embryo sac and, upon reaching the egg, bursts, which allows sperm to penetrate into it. One sperm copulates with the egg, forming zygote giving rise to the embryo. The second sperm fuses with the secondary diploid nucleus located in the center of the embryo sac, resulting in the formation of a triploid nucleus. As a result, a triploid cell is formed, developing into a special nutritious tissue - endosperm(e) (from Greek. endon- inside, sperma- seed). Thus it happens double fertilization, characteristic only of angiosperms. It was first described in 1898 by the outstanding Russian cytologist embryologist S.G. Navashin. Other cells of the embryo sac - antipodes and synergids - are destroyed.
The biological meaning of double fertilization is that triploid endosperm develops only in the case of fertilization, which achieves significant savings in energy and plastic resources, in contrast to gymnosperms, in which the formation of endosperm is not associated with fertilization.
In angiosperms, the endosperm is called secondary, or protein. Only in angiosperms the embryo (sporophase) begins its development independently due to the triploid phase. In all previous groups (gymnosperms, etc.), the embryo develops through gametophase.
Thus, from the constituent parts of the flower the following are formed:
From a fertilized egg - embryo(2n);
Diploid nucleus - endosperm(3p);
Integuments of the ovule - seed coat(2n);
Nucellus - perisperm of seed(2p);
The wall of the ovary and often with the participation of other elements of the flower (calyx, receptacle) - the wall of the fruit (pericarp).
The pericarp consists of three layers: outer - exocarp, average - mesocarp and internal - endocarp.
In many flowering plants (about 10% of species) in the process of evolution sexual reproduction replaced various forms asexual. Of these, the most famous apomixis, in which seeds in apomictic plants are formed without fertilization. In this case, there is no exchange of genetic information, therefore all apomictic individuals have the same genetic and somatic constitution. A good example of a plant with apomictic seed formation according to the type of parthenogenesis is dandelion, which is distinguished by its high viability. Often, especially in perennial rhizomatous plants, vegetative propagation predominates, and seed propagation is suppressed.
INFLORATIONS
Inflorescence called a shoot or a system of specialized shoots that bear flowers. Inflorescences are characteristic of most flowering plants. They have a main axis (inflorescence axis) and lateral axes. The lateral axes may be branched or unbranched and bear flowers. On the axes of the inflorescences there are nodes and internodes. At the nodes of the first order axes there are bracts, and at the nodes of the second order axes there are bracts.
The biological meaning of the appearance of an inflorescence lies in the increasing probability of pollination of flowers in both entomophilous and anemophilous plants. Undoubtedly, inflorescences are more noticeable among the green leaves than single flowers, and an insect will visit many more flowers per unit of time if they are collected in inflorescences. Usually the inflorescences are grouped near the top of the plant, at the ends of the branches, but sometimes, especially in tropical trees, they appear on trunks and thick branches. This phenomenon is known as caulifloria(from Greek caulis- stem and lat. flos- flower). An example is the chocolate tree. (Theobroma cacao). It is believed that in tropical forest conditions, cauliflory makes flowers more accessible to pollinating insects. The presence of inflorescences protects the plant from infertility in the event of the death of a single flower.
Depending on the degree of branching of the axes, simple and complex inflorescences are distinguished. U simple inflorescences on main axis single flowers are located (bird cherry, plantain, sunflower); at complex inflorescences- not single flowers, but lateral axes (clover officinalis, lilac, wheat, bluegrass). In some plants, the apical meristems are spent on the formation of the apical flower, and in this case the inflorescences are classified as closed (sympodial), or uncertain. In closed inflorescences, the apical flowers usually open earlier than the underlying lateral ones, and therefore they are called Verchaceae. In other plants, the apical meristems remain in a vegetative state, and such inflorescences are called open (monopodial), or uncertain. In open inflorescences, the flowers bloom sequentially from bottom to top, which is why they are called side-flowering.
The classification of inflorescences is quite complex, but reference books and guides take into account two characteristics: the nature of branching and the method of growth.
SEE MORE:
Flowering (angiosperms) plants belong to seed plants (along with gymnosperms) and, therefore, sexual reproduction in them is carried out with the help of seeds. Moreover, only in flowering plants during sexual reproduction is the phenomenon of double fertilization observed. It was discovered in 1898 by scientist S. Navashin.
The essence of double fertilization is that in flowering plants two sperm are involved in fertilization. One of them fertilizes the egg, resulting in the formation of a zygote. The second sperm fertilizes the so-called central cell, from which storage tissue (endosperm) develops. In this case, a double set of chromosomes is restored in the zygote, and a triple set in the future endosperm (which is unique). Below, the process of double fertilization in flowering plants is described in more detail.
In the stamens, in their pollen sacs, pollen grains mature. Each pollen grain contains two cells: vegetative and generative.
An ovule develops in the ovary of the pistil (one, several or many depending on the type of plant). Inside the ovule, as a result of division, eight cells are formed containing a single set of chromosomes (gametophyte). Two of these cells fuse to form the central cell. Another one of these cells becomes an egg.
When a pollen grain lands on the stigma, the vegetative cell of the grain forms a pollen tube, which grows through the tissues of the pistil and penetrates the ovule.
For this purpose, there is a special hole in the ovule - the pollen duct.
The generative cell of a pollen grain divides and forms two sperm cells. They penetrate the pollen tube into the ovule. One sperm fertilizes the egg, forming a zygote containing a double set of chromosomes. The second sperm fuses with the central cell, resulting in a cell with a triple set of chromosomes.
As a result of numerous divisions, the zygote develops into the embryo of a new plant. As a result of the division of the central cell, endosperm (nutritive tissue for the embryo) is formed. The walls of the ovule become the seed coat. Thus, the ovule becomes a seed.
The ovary of the pistil transforms into a fruit. Sometimes not only the ovary, but also other parts of the flower are involved in the formation of the fruit. The fruit is a peculiar adaptation of flowering plants to the dissemination of seeds. The variety of possible methods of distribution (with the help of animals, wind, water, self-dispersal) has given rise to a huge variety of angiosperm fruits.
"Leather Lessons" - Academic subject: biology Project participants: 8th grade students. Mechanism and methods of hardening. Learn to use different sources of information. The project is designed for 8th grade students and is implemented in the subject areas of biology and life sciences. Creative project name: Clothes for every day. Is what is fashionable always useful?
“Garden Dormouse” - Pointed muzzle. The ears are relatively large, without tufts. Eats small rodents, chicks and bird eggs. The nest is spherical, located in hollows or tree branches. Found in deciduous forests and old gardens throughout much of Europe. Active at dusk and at night, feeding in trees, less often on the ground. The garden dormouse is a species of rodent of the Dormouse family.
“Primates” - Suborders and families of the Wet-nosed (Strepsirrhini). The classification of primates has undergone significant changes. The earliest primates most likely spread from Asia. Classification. Origin and immediate family. Suborders and families Dry-nosed. Practical significance. General characteristics.
“Theories of the origin of living things” - Additional question. History of performances. The work of judges. Lesson structure. Transition diagram chemical evolution. Matter. Debate. History of ideas about the origin of life. Lesson stage. Hypotheses about the origin of life. Game regulations. Modern hypotheses. Rules of judicial ethics. Nebula. Theories of origin.
“Escape biology” - Interclass. Sedentary Durable Zool... mushrooms Anat... bact - procar. Crown formation. The science. Water. Cells. Ust. Chlorophyll. LEIKO plastids...Young green. Image. Core. Sheet. I. Reproductive organ. A flower is a modified shoot. Rast Bot... alive eukar. Bud - zach leaf. honor Straight. Prob. Cover. Perist. CONDITION water min. salts protein fat carbohydrates whoa.
“Basic concepts of genetics” - What are the genotypes of all individuals? Formulate conclusions by completing the sentences: Genetics: history of the development of science. Consolidation. Locus is the location of a gene on chromosomes. Genesis - origin) is the science of heredity and variability of organisms. By studying genetics, I want to _____________. Introduce the logic of scientific discovery.
Double fertilization 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 - lily (Lilium martagon) and hazel grouse (Fritillaria orientalis). In D. o. both sperm are involved, brought into the embryo sac by the pollen tube; nucleus of one sperm (See. Sperm) fuses with the nucleus of the egg, the nucleus of the second - with the polar nuclei or with the secondary nucleus of the embryo sac. Develops from a fertilized egg Germ ,
from the central cell - Endosperm. In embryo sacs with a three-celled egg apparatus, the contents of the pollen tube are usually poured into one of the synergids (See. Synergids),
which is destroyed (the remains of the synergid nucleus and the vegetative nucleus of the pollen tube are visible in it); the second synergid subsequently dies off. Next, both sperm, together with the modified cytoplasm of the pollen tube, move into the slit-like gap between the egg and the central cell. Then the sperm separate: one of them penetrates the egg and comes into contact with its nucleus, the other penetrates 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 upon penetration into the embryo sac; sometimes sperm in the form of unchanged cells are observed in the embryo sac. With D. o. The 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 Asteraceae, the sperm nuclei have the appearance of a double twisted or crimped chromatin thread; in many plants they are elongated, sometimes crimped, more or less chromatized, and do not have nucleoli; usually sperm are round interphase nuclei with nucleoli, sometimes not different in structure from female nuclei. Based on the nature of the unification of male and female nuclei, it was proposed (E. N. Gerasimova-Navashina) to distinguish between two types of D. o.: premitotic - the sperm nucleus is immersed in the female nucleus, its chromosomes are despiralized; the union of the chromosome sets of both nuclei occurs in 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. With D. o. In the egg, 2 haploid nuclei fuse, so the zygote nucleus is diploid. The number of chromosomes in the endosperm nuclei 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. - Ksenia -
manifestation of dominant traits of the endosperm of the paternal plant in the endosperm of hybrid seeds. If several pollen tubes penetrate into the embryo sac, the sperm of the first one participates in pollen formation, while the sperm of the others degenerate. Cases of dispermia, i.e. fertilization of an egg by two sperm, are very rare. Lit.: Navashin S. G., Izbr. works, vol. 1, M.-L., 1951; Mageshwar and P., Embryology of Angiosperms, 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.
Big Soviet encyclopedia. - M.: Soviet Encyclopedia. 1969-1978 .
See what “Double fertilization” is in other dictionaries:
Characteristic only of flowering plants. During 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 embryo develops from the central cell... ... Big Encyclopedic Dictionary
A type of sexual process characteristic only of flowering plants. Discovered in 1898 by S. G. Navashin in Liliaceae. Before. lies in the fact that when a seed is formed, not only the egg is fertilized, but also the center, the nucleus of the embryo sac. From a zygote... ...
double fertilization- A 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 Guide
Characteristic only of flowering plants. During 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 embryo develops from the central cell... ... encyclopedic Dictionary
Double fertilization double fertilization. A type of sexual process characteristic of flowering plants: one of the sperm fertilizes the egg, and the other (from the same pollen tube
Characteristic only of flowering zones. With D. o. one of the sperm fuses with the egg, and the second with the center. embryo sac cell. An embryo develops from a fertilized egg, 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 spermatozoa are formed. One of them fuses with the egg, the second - with the central diploid cell of the embryo sac. Discovered by S. G. Navashin in... ... Anatomy and morphology of plants
DOUBLE FERTILIZATION- a sexual process in angiosperms, consisting 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... Dictionary of botanical terms
double fertilization according to nawashin- PLANT EMBRYOLOGY DOUBLE FERTILIZATION ACCORDING TO NAVASHINA - the fusion of an egg and a sperm to form a zygote (2p) and the simultaneous fusion of another sperm and a double nucleus to form the primary endosperm nucleus (3p). Feature everyone... General embryology: Terminological dictionary
Syngamy, the fusion of a male reproductive cell (sperm, sperm) with a female (egg, ovum), leading to the formation of a zygote, gives rise to a new organism. In animals O. is preceded by insemination. In the process of O., the egg is activated,... ... Biological encyclopedic dictionary
James Dewey Watson - American molecular biologist, geneticist and zoologist; He is best known for his participation in the discovery of the structure of DNA in 1953. Winner of the Nobel Prize in Physiology or Medicine.
After successfully graduating from the University of Chicago and Indiana University, Watson spent some time doing chemistry research with biochemist Herman Kalckar in Copenhagen. He later moved to the Cavendish Laboratory at the University of Cambridge, where he first met his future colleague and comrade Francis Crick.
Watson and Crick came up with the idea of a DNA double helix in mid-March 1953, while studying experimental data collected by Rosalind Franklin and Maurice Wilkins. The discovery was announced by Sir Lawrence Bragg, director of the Cavendish Laboratory; this happened in belgian scientific conference April 8, 1953. The important statement, however, was not actually noticed by the press. On April 25, 1953, an article about the discovery was published in the scientific journal Nature. Other biological scientists and a number of Nobel laureates quickly appreciated the monumentality of the discovery; some even called it the greatest scientific discovery 20th century.
In 1962, Watson, Crick and Wilkins received the Nobel Prize in Physiology or Medicine for their discovery. The fourth participant in the project, Rosalind Franklin, died in 1958 and, as a result, could no longer qualify for the prize. Watson was also awarded a monument at the American Museum of Natural History in New York for his discovery; since such monuments are erected only in honor of American scientists, Crick and Wilkins were left without monuments.
Watson is still considered one of the greatest scientists in history; however, many people openly disliked him as a person. James Watson has been involved in quite high-profile scandals several times; one of them was directly related to his work - the fact is that while working on the DNA model, Watson and Crick used data obtained by Rosalind Franklin without her permission. The scientists worked quite actively with Franklin's partner, Wilkins; Rosalind herself, quite possibly, might not have known until the end of her life how important the role her experiments played in understanding the structure of DNA.
From 1956 to 1976, Watson worked at Harvard's biology department; During this period he was interested mainly in molecular biology.
In 1968, Watson received a position as director of the Cold Spring Harbor Laboratory in Long Island, New York; Thanks to his efforts, the quality level in the laboratory has significantly increased research work, and financing has improved markedly. Watson himself was primarily involved in cancer research during this period; Along the way, he made the laboratory under his control one of the best centers of molecular biology in the world.
Watson became president in 1994 research center, in 2004 – rector; in 2007, he left his position after making rather unpopular statements about the existence of a connection between intelligence level and origin.
Best of the day
| The terrible story of the SKA hockey player Visited:768 |
Love and illness Visited:210 |
