Schizogenesis, also known as schizogenesis, is a common asexual reproductive mode, that is, the reproductive mode in which the mother splits into two (binary fission) or more (dichotomous) new individuals with the same size and shape. This way of reproduction is common in single-celled organisms, but for different single-celled organisms, the way of nuclear division is different in the process of reproduction, which can be summarized as follows:
1 asexual reproduction by amitosis.
Amitosis, also called direct division, is the simplest cell division. During the whole division process, the ratio of spindle filament to chromosome remains unchanged, which is the most common in the division and reproduction of prokaryotes such as bacteria and cyanobacteria.
The division of prokaryotic cells includes two aspects: (1) the distribution of cell DNA, so that the divided daughter cells can get a whole set of genetic material of the mother cell; (2) Cytokinesis basically divides cells into two equal parts.
The two copied DNA molecules are connected to the plasma membrane. As the cell grows, two DNA molecules are pulled apart. When cells divide, the cell wall and plasma membrane fold, and finally the mother cell divides into two roughly equal daughter cells.
Vegetative division and reproduction by mitosis.
The process of mitosis is much more complicated than amitosis, and it is the main way of cell division in multicellular organisms. However, some single cells, such as dinoflagellate, euglena and amoeba, also divide and reproduce through mitosis.
(1) The chromosome structure and unique mitosis of dinoflagellate cells have the dual characteristics of eukaryotic cells and prokaryotic cells. When the cell begins to divide, the nuclear membrane does not disappear, and the chromosomes in the nucleus overlap with the nuclear membrane. During cell division, the middle of the nuclear membrane contracts inward to form a groove, and the cytoplasm in the groove has a spindle-like structure with microtubules arranged in the same direction, which regulates the nuclear membrane and chromosomes and divides into daughter cells, and finally divides into two daughter cells (dinoflagellate).
(2) During the division and reproduction of euglena, the nucleus undergoes mitosis, and the nuclear membrane does not disappear during the division. With the contraction of the middle part of the nucleus, it divides into two subnuclei, and then the cell divides into two longitudinally from front to back (longitudinal binary division), one of which has protoflagella and the other grows new flagella, thus forming two euglena.
(3) When the amoeba grows to a certain size, it divides and reproduces, which is a typical mitosis and the nuclear membrane disappears. With the contraction of the middle part of the nucleus, chromosomes are distributed to the daughter nucleus, and then the cytoplasm is divided into two, which divides the cell into two offspring individuals.
Asexual division and reproduction through amitosis and mitosis.
The most typical representative of this method is paramecium, which belongs to protozoan ciliates. There are two types of nuclei in the cell, namely, large nucleus and small nucleus. Small nucleus is reproductive nucleus and large nucleus is vegetative nucleus. When paramecium reproduces asexually, the small nucleus undergoes mitosis, the large nucleus undergoes amitosis, and then the worm divides into two new individuals from the middle.
Bud propagation, also called bud propagation, is one of the ways of asexual propagation.
The "bud" in "bud grafting propagation" refers to the bud body growing on the mother body, not the structure of the real bud on higher plants.
Parents produce offspring through cell division, and a bud similar to the mother grows in a certain part, that is, the bud base. Bud base does not leave the mother immediately, but is connected with the mother and continues to receive nutrition from the mother until the individual can live independently. It is a special way of asexual reproduction, such as coelenterates and sponges.
Some creatures will form spherical buds from the side of their bodies under appropriate circumstances. The nutrition of this bud is provided by the mother. When they mature, they will form a new body wall at the junction of the mother, and then leave the mother and become independent new individuals. This phenomenon is called budding reproduction.
Spores and cysts of ferns. In lobular pteridophytes, sporangium is solitary in leaf axils or leaf bases near spore leaves. Usually, many spore leaves gather tightly or loosely at the top of branches to form spherical or spikes, which are called cones or spore discs, such as Lycopodium and Equisetum. Ferns with large leaves do not form spikes of spore leaves, and sporangia are not only born in the axils of leaves, but gather into sporangia groups or cysts of different shapes, which are born on the back or edge of spore leaves. The cell wall of sporangium is composed of single-layer (Pteris gracilis) or multi-layer (Pteris gracilis) cells, and the cell wall is unevenly thickened to form a ring. The position of the ring has many forms, such as end ring, transverse central ring, oblique ring, vertical ring and so on. These annuals play an important role in spore transmission. The sporangium wall consists of multiple layers of cells (thick-stalked hyphae) or one layer of cells (thin-stalked hyphae). Some cells in the sporangium wall often thicken unevenly and are arranged in bands, which are called bands. The girdle is terminal, transverse to the middle, oblique and vertical. Most ferns produce spores with the same shape and size, which are called isospores. A few ferns, such as Selaginella Selaginella and Pteridium aquaticum, have different spore sizes, that is, there are megaspores and microspores, which are called heterospores. The saccular structure that produces megaspore is called megaspore, and microspore is called microspore. The megaspore germinates to form female gametophyte, and the microspore germinates to form male gametophyte.
Sporangia often aggregate to form sporangia groups (piles). There are many ways to attach sporangium. The prototype is born on the specialized spore leaves at the top of the branch and becomes a spike or cone-shaped sporangium spike. Evolutionary types include: marginal sporangium, which means that sporangium is attached to the edge of feather, and the terminal sporangium is born at the top of feather; Vein-end sporangium group, born at the top of veinlets, dorsal sporangium group, born in the middle of veinlets, cave sporangium group, born in concave spots formed by pinna, and also covered by leaves. Sporangium is covered and uncovered. Sporangium has many shapes, such as round, kidney and strip.
Spores are usually double-sided, four-sided or spherical, with smooth outer walls or ridges, spines or elastic filaments. Most species of spores are one type, and a few species are heteromorphic (such as Selaginella), that is, there are large and small spores. There are about 12000 species of pteridophytes, about 2600 species in China, and many medicinal plants.
fungal spore
1) zoospores: formed in zoosporangium. The swimming sporangium is formed by the expansion of mycelium or the top of sporangium. Zoospores have no cell wall and have 1-2 flagella, which can swim in water after release.
(2) sporangium spores: formed in sporangium. Sporangium is formed by the swelling of the top of sporangium. Ascomycetes have cell walls and no flagella, and can fly with the wind after being released.
(3) Conidia are produced on the conidiophore formed by the differentiation of hyphae, and grow terminal, laterally or crosswise, with different shapes and sizes. They are single-celled or multi-celled, colorless or colored, and fall off from the robe handle when they mature. Conidia and conidiophore of some fungi are still embedded in conidia. There are two main types of fruit, that is, nearly spherical meristem and cup-shaped or disk-shaped apetalous meristem
2. Sexual reproduction fungi grow and develop to a certain period (usually to the later stage) for sexual reproduction. Sexual reproduction is a way of reproduction in which two sexual cells combine and the nucleus undergoes meiosis to produce robes. Most fungi differentiate from hyphae to produce gametophytes, which are sex organs and form sexual vesicles through the combination of male and female gametophytes. The whole process can be divided into three stages: mass matching, nuclear matching and meiosis. The first stage is mass matching, that is, after the fusion of two sex cells, the cytoplasm and nucleus (N) of the two cells are fused in the same cell to form a binuclear phase (N+N). The second stage is nuclear matching, that is, two haploid nuclei are combined into a diploid nucleus (2N) in the fusion cell. The third stage is meiosis, in which diploid nuclei undergo two successive divisions to form four haploid nuclei (N), thus returning to the initial haploid stage. Fungi can produce four types of sexual spores after sexual reproduction.
Oospore: the sexual spore of oomycete. After the two heterozygotes-male organ and egg storage-contact, the cytoplasm and nucleus of male organ enter the egg storage through the insemination tube, which matches with the nucleus of the egg ball, and finally the fertilized egg ball develops into a thick-walled diploid oospore.
(2) Conjunctive spores: the sexual spores of zygobacteria. It is a thick-walled spore formed by the fusion of two gametophytes into 1 cell in the way of gametophyte combination, and the mass matching and nuclear matching in this cell.
(3) Ascomycetes: the sexual spores of Ascomycetes. Usually, it is a haploid spore formed by the combination of two heterogametes, male organs and ascomycetes through mass matching, nuclear matching and meiosis. Ascomycetes are attached to colorless, transparent, rod-shaped or oval cystic structures, which are called ascomycetes. Usually, 8 ascospores are formed in each ascocyst. Ascomycetes are usually produced in the covered fruit. Ascomycetes are generally divided into four types, namely, spherical closed capsules without holes, bottle-shaped or spherical capsules with true shell walls and fixed holes, sub-chambers without true shell walls and fixed holes due to seat disintegration, and disk-shaped or cup-shaped pistils.
(4) Basidiospores: sexual spores of basidiomycetes. Usually, "+"and "-"hyphae directly combine to form binuclear hyphae, and then the cells at the top of binuclear hyphae expand into rod-shaped burdens. After nuclear pairing and meiosis, four exogenous haploid basidiospores are produced on the basidium.
In addition, some lower fungi, such as Rhizopus, produce sexual spores. And hypha species. It is a thick-walled resting spore, which is formed by the combination of swimming gametes and then developed from fertilized eggs.
Fungal spores can reproduce without water.
Spores produced by plants through asexual reproduction are called "asexual spores", such as conidia, sporangium spores and zoospores. Spores produced by sexual reproduction are called "sexual spores", such as zygospores, oospores, ascospores and basidiospores. Spores that can directly resist adverse environmental conditions by thickening the cell wall and storing nutrients by vegetative cells. ...
Vegetative reproduction is a part of the vegetative organs of higher plants-roots, stems and leaves, which develop into a new individual after falling off from the mother.
For example, the creeping branches of strawberries, the roots of thistles and the leaves of begonia can sprout from buds and form new individuals.
Vegetative propagation is a way of propagation in which vegetative organs such as roots, stems and leaves of higher plants develop into new individuals. Such as tuber propagation of sweet potato, creeping propagation of strawberry, rhizome propagation of bamboo, reed, white spear and lotus, tuber propagation of potato, bulb propagation of lily and onion, bulb propagation of narcissus and taro, and leaf bud propagation of begonia are all natural nutrition propagation. In agriculture, forestry and horticulture, rooting, cutting, layering, grafting and other methods are often used to separate a part of plant vegetative organs from the mother body and make them develop into new individuals, which belongs to artificial nutritional reproduction. Tissue culture is also a method of artificial nutrition reproduction. Asexual reproduction can enable offspring to maintain the excellent characteristics of their parents. Therefore, flowers, fruit trees, tea, sugarcane, bamboo and other artificially cultivated plants all adopt this propagation method.
Brief history of plant tissue culture development Plant tissue culture is a biotechnology developed in the early 1930s. It is a method of cultivating plant organs, tissues, cells, protoplasts and other substances in a sterile state on an artificially prepared culture medium.
Totipotency of plant cells is the theoretical basis of plant tissue culture. At the beginning of the 20th century, people asked whether the parenchyma cells of plants could be cultured into complete plants. The researchers took a piece of tissue from the phloem of carrot root, cultured it in liquid medium, differentiated it into callus, and obtained embryoids from the callus. After the embryoids were transferred to solid medium for further culture, complete carrot test-tube plants were obtained. After cultivation, this plant can grow normally, blossom and bear fruit, and the offspring produced by its seeds are no different from those produced by the seeds of normal plants. According to this experiment, we can draw the following conclusions: the parenchyma cells of plants can be cultured into complete plants like the mother without sexual reproduction. Because every nucleated cell of a plant carries all the genes of its mother, it can develop into a complete plant under certain conditions, which is called plant cell totipotency.
Scientists' achievements in organ formation induced by plant hormones and improvement of medium formula have greatly promoted the development of tissue culture technology, which can be applied to rapid propagation and variety improvement. In the early 1950s, French scientists successfully removed the virus carried by infected Dahlia plants by tissue culture technology, thus providing a feasible way to produce virus-free seedlings. Nowadays, using tissue culture technology to remove plant viruses has been widely used in production. In the mid-1950s, due to the discovery of cytokinin, the morphogenesis of explant buds in tissue culture became a man-made controllable factor, thus making plant regeneration in tissue culture a reality. Since 1960s, tissue culture technology has made continuous progress in basic theory and practical operation, and has made gratifying achievements in plant somatic hybridization, haploid breeding, germplasm preservation, rapid seedling raising, artificial seed production, secondary metabolites production and so on. Nowadays, tissue culture technology has become a solid foundation, easy to master and widely used technical means.
Corpus callosum and corpus callosum originally refer to the new tissue on the wound surface after the local plant is stimulated by trauma. It is composed of living parenchyma cells and can be derived from living cells of various tissues in any organ of plants. In the injured part of the plant, callus can help the wound heal; In grafting, it can promote the healing of rootstock and scion, and make rootstock and scion communicate with each other through new vascular tissue; In cutting, wound callus can differentiate into adventitious roots or buds, and then form a complete plant. When plant organs, tissues and cells are cultured in vitro, callus can also grow under suitable conditions. The process of its occurrence is to induce the living cells in the explants to restore their potential totipotency and transform them into meristem cells, and then the derived cells differentiate into parenchyma to form callus. Callus produced by in vitro culture of plant organs, tissues and cells can further induce organ regeneration or embryoid formation into plants under certain conditions. In haploid breeding, callus or embryoid produced by pollen can also differentiate into haploid plants. Protoplast culture can even induce plant or organ regeneration. Therefore, the concept of callus is not limited to the new tissue in the injured part of plants.
In plant tissue culture, the formation of typical callus from explants usually goes through three stages: initiation, division and formation. Start-up refers to the period when cells are ready to divide. Exogenous plant growth hormone has a good effect on inducing cell division. Commonly used are naphthylacetic acid, indoleacetic acid and cytokinin. Generally, the ratio of cytokinin to auxin is 1∶ 1 to induce callus formation of plant materials. For example, is MS+6-BA6-BA a synthetic cytokinin 6? Short for base adenine. 0.5 mg/L+IBAIBA is the abbreviation of indolebutyric acid, which is a synthetic auxin. 0.5 mg/L. Mitosis refers to the dedifferentiation process of explant cells after the induction, continuous division and proliferation of daughter cells. Mitotic callus is characterized by rapid cell division, loose structure and light and transparent color. Differentiation refers to a series of morphological and physiological changes of cells at the end of division, thus producing cells with different shapes and functions in callus. These cell types include parenchyma cells, meristem cells, pigment cells, fibroblasts and so on. After a series of changes, such as start-up, division and differentiation, explant cells form callus with disordered structure. If we continue to cultivate callus on the original medium, it will stop growing, even aging, blackening and death because of insufficient nutrition or the accumulation of toxic metabolites in the medium. If the callus continues to grow and proliferate, it must be divided into small pieces regularly (2 ~ 4 weeks) and inoculated on fresh culture medium to keep the callus growing vigorously for a long time.
The morphogenesis of callus is the callus produced through the stages of start-up, division and differentiation, in which although cell differentiation has taken place, there is no organogenesis. Only when certain conditions are met can the cells of callus differentiate again, produce buds and roots, and then develop into complete plants. In tissue culture, higher cytokinin and lower auxin ratio are generally used to induce bud formation, such as MS+6-BA 1 mg/L+IAA(IAA is short for auxin 3- indoleacetic acid). ) 0. 1 mg/l and 1/2MS+IAA0. 1 mg/L can induce rooting. Of course, different plant species, different growth states, and the proportion of hormones will change greatly, so we need to explore and accumulate experience in practice.
definition
Parents do not produce reproductive patterns of offspring individuals through the combination of bisexual cells. More common in invertebrates. Also known as apogamy. Refers to the general term for reproduction modes unrelated to gametes. This is a copy of sexual reproduction. Including fission propagation, budding propagation, spore propagation, vegetative propagation, tissue culture and so on. The advantage of asexual reproduction is that it can keep the characteristics of the female parent. In essence, somatic reproduction is asexual reproduction.
Reproduction is the phenomenon that parents produce offspring. Is one of the basic characteristics of living things. Any living thing has the ability to breed offspring and race. Biological reproduction includes asexual reproduction and sexual reproduction.
kind
There are several ways of asexual reproduction:
1, fission reproduction, also known as fission, is a reproductive mode in which an organism splits from its mother to produce new offspring. The new individuals produced by division and reproduction are roughly the same in size and shape. In single-celled organisms, this mode of reproduction is more common. For example, paramecium, amoeba and bacteria all divide and reproduce.
The division and reproduction of amoeba is shown in the upper right picture.
2. Bud reproduction Bud reproduction is also called bud reproduction, which is a reproductive mode in which the mother gives birth to buds in a certain part. The bud gradually grows up, forms the same individual as the mother, falls off from the mother and becomes a complete new individual. Yeast and hydra (when the environment is bad, hydra also has sexual reproduction. ) often bud and reproduce.
3. Spore reproduction Some organisms can produce a kind of cell when they grow up, which can directly form a new individual without pairing. This cell is called spore, and this reproduction is called spore reproduction. For example, Rhizopus forms sporangia at the top of its upright mycelium, producing spores. Spores can develop into new rhizopus when they fall in a humid and warm environment rich in organic matter. Generally speaking, lower plants and fungi reproduce in this way. Such as Adiantum, Penicillium and Aspergillus.
4, vegetative reproduction by the vegetative organs of plants (roots, leaves, stems) to produce a new way of individual reproduction, called vegetative reproduction. For example, the tubers of potatoes, the roots of thistles, the creeping branches of strawberries and the leaves of begonia can all germinate, and these buds can form new individuals.
Nutritional reproduction can make offspring keep their parents' traits, so people often use artificial methods such as rooting, cutting and grafting to propagate flowers and trees.
The vegetative propagation in the natural state is called natural vegetative propagation. Such as strawberry creeping branches, begonia leaves and potato tubers; Artificial assisted vegetative propagation is called artificial vegetative propagation. Such as cutting and grafting
Cutting: Cut branches into small pieces, insert them into the soil, and take root and sprout into new plants.
Grafting: Grafting the branches (or buds) of one plant to the branches of another plant, so that the cambium of the two plants is aligned, so that they can heal each other and grow into a plant.
Scion: a grafted bud or branch.
Rootstock: a grafted plant
Survival principle: use the regenerative ability of cambium.
The key to survival: pay attention to make the cambium of scion and rootstock close together. In this way, the cells split from the cambium combine the scion with the rootstock.
The conditions for asexual propagation of plants such as cuttings are as follows: 1. Stem segments (keep two segments), the upper incision is horizontal and the lower incision is inclined, except for environmental conditions such as light, moisture, temperature and humidity; 2. Blade: the last section is removed, and the next section is completely removed.
5. Tissue culture
Plant cells are omnipotent. According to this theory, plant propagation can be completed by using plant tissue culture technology. The general process of plant tissue culture is as follows: under aseptic conditions, plant organs or tissues are cut off and cultured on suitable human culture medium, and these organs or tissues will undergo cell division and form new tissues. However, there is no cell differentiation in this tissue. Under the conditions of proper illumination, temperature and certain nutrients and hormones, these cells begin to differentiate, produce tissues and organs, and then develop into complete plants.
Plant tissue culture not only has less materials, short culture period and high reproduction rate, but also is convenient for automatic management. This technology has been widely used in the rapid propagation of fruit trees and flowers and the cultivation of virus-free plants. For example, the shoot tips of orchids and chrysanthemums can produce 400,000 orchid seedlings a year. For another example, plants that reproduce asexually for a long time often accumulate a large number of viruses in their bodies, thus affecting the yield and ornamental value of plants. It has been found that only the shoot tip and root tip are virus-free. Therefore, many virus-free strains of plants, such as potato, Gramineae and chrysanthemum, have been obtained by tissue culture from shoot tips, and considerable economic benefits have been achieved.
6. Cloning
explain
1, single-celled organisms can only divide and reproduce.
2. The "bud" in "bud grafting propagation" refers to the bud growing on the mother, not the structure of the real bud on higher plants. For example, potatoes are propagated by buds or tubers, which are vegetative rather than budding. In essence, the "bud" is the same as the mother, but the bud is smaller.
3. Spores in asexual reproduction "spores" in asexual reproduction are asexual spores with the same number of chromosomes or DNA as somatic cells. Therefore, asexual spores can only be produced by mitosis or amitosis, but not by meiosis.
4. Vegetative reproduction is reproduction by using vegetative organs of plants. Only higher plants can differentiate roots and leaves. Therefore, it is an asexual reproduction mode of higher plants, and it is impossible for lower plant cells to carry out vegetative reproduction.