\u003e\u003e Seed and Fruit Formation
Section 46. Formation of seeds and fruits
What happens in the ovule after fertilization? The fertilized egg divides in two cells... Each of the cells that arose in this process divides again, etc. As a result of repeated cell divisions, a multicellular embryo of a new plants.
From the largest ovule cell, which fuses with the second sperm, endosperm cells develop, in which nutrient reserves are accumulated. The endosperm supplies the developing embryo with them.
The seed coat develops from the ovule cover. So, after fertilization, a seed, consisting of a peel and an embryo, develops from the ovule.
Lesson content lesson outline support frame lesson presentation accelerative methods interactive technologies Practice tasks and exercises self-test workshops, trainings, cases, quests home assignments discussion questions rhetorical questions from students Illustrations audio, video clips and multimedia photos, pictures charts, tables, schemes humor, jokes, fun, comics parables, sayings, crosswords, quotes Supplements abstracts articles chips for the curious cheat sheets textbooks basic and additional vocabulary of terms others Improving textbooks and lessons bug fixes in the tutorial updating a fragment in the textbook elements of innovation in the lesson replacing outdated knowledge with new ones For teachers only perfect lessons calendar plan for the year guidelines discussion agenda Integrated lessonsMany different concepts are studied in a botany course. One of them is endosperm. What is it, what functions does this structure perform in a plant? You will find the answer to these and other questions in this article.
Endosperm is part of the embryo
People have long been amazed at the ability of a tiny seed to give rise to an entire organism. It turns out that this is due to its unique consists of an embryonic root, stalk, bud and leaf. These embryonic structures are surrounded by nutritive connective tissue. She is the endosperm. Outside the seed has additional protection - the peel.
This term comes from two Greek words "endo" - inside, "sperm" - seed. Essentially, the substances required for the development of the tissues of the embryo.
The value of nutrients
Endosperm is tissue that forms during fertilization. By chemical composition it is a complex of starch carbohydrates, proteins and vegetable oils... Therefore, a person uses seeds as a source of energy and vitamins. But beneficial features they are kept only raw. When heat treatment the destruction of macromolecules of organic substances occurs.
Endosperm of gymnosperms
Plant nutritional tissue can be primary and secondary. In gymnosperms, endosperm is formed even before the process of gamete fusion - fertilization. It develops from a megaspore, which is a mother cell with a haploid set of chromosomes. The primary endosperm is tissue that forms in the ovule. As a result of its development, a female overgrowth, or gametophyte, is formed.
Double fertilization of plants
In the seeds, the angiosperm endosperm is formed during fertilization. During this process, two sperm are involved, which are located in the anthers of the stamen. The pistil ovary contains one female gamete and a central germ cell. Fertilization takes place here. One sperm is fused with the egg to form the seed embryo. The other connects to the germ cell. The result of the latter process is endosperm. This type of its formation is called secondary. The endosperm is located around the embryo, warming and nourishing it, creating conditions for the germination of the seed.
How is it formed?
Endosperm is formed in two ways. In the first case, the fertilized nucleus embryo sac is shared many times. The resulting structures are located along its walls. This type of endosperm formation is called nuclear. In this case, the nutrient tissue of the seeds is liquid. Take coconut milk, for example.
But in most angiosperms, after nuclear division, cellular division occurs. It changes the state of aggregation of the nutrient tissue. Moreover, cells are formed during each division. So, if you collect the fruits of corn during the period of nuclear fission, it will be juicy and sweet. This is followed by the transformation of simple carbohydrates into polysaccharides. This chemical transformation accompanies cell division.
So, the endosperm, which is the nutrient of the embryo of the seed, performs essential functions. These include providing the embryo with energy, vitamins and microelements, and transporting solutions of minerals from an adult plant. Also important is the regulation of the process of differentiation of embryonic cells into organs, which occurs due to the cytokinins of the endosperm.
Order of the Palm (Bincipes)
Palm family (Palmae, or Arecaceae)
Trees, sometimes lianas with unbranched trunks, without secondary thickening and a crown of palmate or pinnately dissected leaves. Flowers are small, bisexual, correct, in simple or complex, often very large inflorescences, sessile or, often, submerged in fleshy axes. The perianth is simple, 3-membered, in 2 circles, sometimes spiral, separately or somewhat intergrowth. 6 stamens in 2 circles, often 9 or more. Filaments are loose or fused at the base into a ring or tube. Ovary superior, 1-3-celled with 1 anatropic ovule with 2 integuments. Column. The placentation is central-angular. The fruit is a berry or drupe. The seeds are large, with endosperm, often closely intergrown with the endocarp.
235 genera and about 3400 species in the tropics and subtropics, especially Asia and America.
The concept of the tropics is rightly associated with palm trees. They often define tropical landscapes. They even talk about the "palm belt", referring to the area of \u200b\u200bcoconut cultivation, between 20 ° latitude north and south of the equator. These latitudes approximately delimit the tropics from the subtropics. Rainforests are especially rich in palm trees on the alluvial soils of such large rivers as the Amazon and Orinoco. But there are many palms in savannas and in mountainous subtropical forests, where they can reach the frost limit. The only European species hamerops low (Chamaerops humilis), which lives in the south of Spain and Italy, can even withstand temperatures of -7 ° C. The geographical distribution of the palms is generally remarkable. In America, 92 genera and 1140 species are known. In the Australian-Asian space, there are only slightly more species - 1150, but 167 genera, which is explained by the high number of genera endemic to individual islands. But Africa has only 50 species from 15 genera.
Many palms are characterized by high columnar trunks up to 20-30 m high, but they have the same thickness throughout, and sometimes the trunk in the upper part is even thicker than at the base due to the remaining petioles of leaves. The secondary thickening in palms, as in almost all monocots, is absent, but the primary thickening is very intense. Below the growth point, a large number of rapidly dividing cells and quite a lot of irregularly located vascular bundles with powerful sclerenchymal sheaths are laid. As the palm grows, the primary thickening may progress and then subside again. In some species, this leads to a swelling of the trunk in the middle part (resembling a boa constrictor that has swallowed large prey).
Palm trunks do not branch, except for the genus hifene (Hyphaene), which is supposed to have real dichotomous branching. Along with the tall-stemmed species, there are many short-stemmed and almost stemless species, in which a rosette of leaves emerges as if out of the ground. Climbing so-called "rattan" palms of the genus are very peculiar calamus (Calamus) living in the tropics of the Old World. Rattans have relatively thin flexible trunks set with strong curved spines. Cirrus leaves in a clearly regular arrangement (not typical for palms!), Have several pairs of lateral segments, as well as densely spiked rachis, which top part sheet. The length of rattan trunks reaches 100-200 m.
There are two main types of palm leaves. The original is the feathery type (Fig. 204). The cirrus-dissected leaves of palm trees reach the maximum size for leaves of 10 m or more, but the usual size is 3-5 m. A leaf of such a palm tree falling down with a noise can seriously hurt. The finger-dissected leaf is phylogenetically secondary and arose as a result of inhibition of the growth of rachis. The segments of the palmate leaf are more or less accrete at the base. The trunks of many palms (and even more often leaf stalks) are strongly thorny.
An interesting problem is the herbarization of palms. Of course, you can collect flowers for a herbarium, often fruits or parts of inflorescences. And what about the leaves, the inflorescence as a whole or with the trunk? Here the herbarium is largely replaced by a sketch, accompanied by the necessary quantitative measurements, for example, the width of the petiole, the number of segments, etc.
Inflorescences of many species often branch intensively and reach significant sizes, sometimes up to 1.5 m or more. Their axes are often thickened and brightly colored. It's amazing that always small flowers palm trees form
Figure: 204. Palms. Coconut (Cocos nucifera): 1 - general form; 2 - inflorescence with male (a) and female (b) flowers; 3 - male flower (part - sepals); 4 - sectional view of the fruit (coconut). Caliptrocalyx (Calyptrocalyx spicatus): 5 - the upper part of the plant with fruits. Sabal (Sabal mauritiiformis): 6 - general view with inflorescences. Bactris (Bactris guineensis): 7 - part of a plant with fruits. Seychelles palm (Lodoicea maldivica): 8 - part female plant with fruits; 9 - bilobed endocarp with seed. Calamus (Calamus longisetus): 10 - cross section of the ovary
sometimes such large fruits as coconut (Cocos nucifera) or seychelles palm (Lodoicea maldivica). The fruits of the latter are the largest among woody plants, and the seeds are generally the largest. So in these respects, palm trees stand as champions.
The importance of palm trees in the life of the population of tropical countries can hardly be overestimated. Finger-cut leaves of many species are common material found on the roofs of so-called palm huts. From the trunks sago palm (Metroxylon) extract the starch contained in the parenchymal cells and used to make real sago. One of the world's most important oilseeds - undoubtedly oil palm (Elaeis guineensis). Fats in an exceptionally high concentration are deposited in this palm not in the endosperm, but in the pericarp, so that they cannot be used by the seedling, but undoubtedly attract animals that distribute the fruits. This African feathery palm is cultivated in many parts of the tropics. Biologically, it is interesting in that it has dioecious inflorescences that bloom at the same time. In the male inflorescences there are up to 140,000 flowers, in the female - no more than 5,000. There are also purely dioecious varieties.
Perhaps the most famous among the palm trees belongs to the pinnate species. coconut palm, or coconutespecially abundant in coastal areas. The landscape of the coastal regions of India, South Vietnam, Cuba, Ceylon is largely determined by the coconut tree. It is assumed that the homeland of the plant is the islands of Polynesia, from where it spread not only through humans, but also by transferring fruits through water. The middle layer of the pericarp is represented by the air layer. The seeds are capable of germination after 3 or even 4 months of swimming. Coconut fruit is not entirely common. Inside the powerful, 3-layered pericarp is a 1 cm thick "shell" of endosperm, to which is adjoined by a tiny embryo. The middle of the fruit is filled with a cloudy liquid rich in proteins - "coconut milk" (its taste, however, has nothing to do with milk). When the "nuts" are fully ripe, 9-11 months after flowering, the liquid solidifies. One inflorescence yields 8-10 "nuts", and the tree yields at least 25-30 years. Coconut endosperm (the so-called copra) is a valuable product used for the manufacture of coconut oil, as well as confectionery. The processing of coconut "nuts" is difficult to mechanize and is still going on by hand, a skilled worker opens 2000 "nuts" per day.
In the huge family of palms, only a few species form edible fruits like the coconut. The latter also include dates - fruits date palm (Phoenix dactylifera). Its origin is unclear, but there is no doubt that it is one of the most ancient cultivated plants... In appearance, the date palm is a little bit like a coconut, but the latter has a smooth trunk, while the date palm is densely covered with the remains of dead leaf stalks. The coconut palm is grown in a humid seaside climate; the date palm, on the other hand, can grow in arid places, right up to desert oases. Her root system can reach deep groundwater. Date palm dioecious. Mostly female trees are planted on plantations, and inflorescences from male palms, which are a subject of trade, are tied in the crowns of female individuals. Fruits - dates - single-seeded berries with juicy sugary mesocarp.
The fruits of the palm tree are of particular use. areca (Areca catechu). They are sold in abundance in any market in South Asia and go to the preparation
narcotic chewing composition - betel nut, which also includes the leaves of one type of black pepper and lime. The alkaloids contained in areca fruits strongly stimulate the central nervous system and inhibit the activity of the heart.
We see in this way that the palms find the most various applications... Here are some more examples. From young inflorescences wine palm (Raphia vinifera) get the sweet juice used to make palm wine. By the way, the leaves of one of the species of this genus reach 15 or even 20 m in length, fiber is extracted from the leaf petioles of many palm species, which is used to make ropes, nets, etc.
Palm trees are extremely decorative. They adorn boulevards and embankments of cities, right up to the coasts of the Mediterranean and Black Seas (however, only the most cold-resistant species can grow here). Some types of palm trees can be seen on national emblems and flags. Royal palm (Roystonea regia), which adorns the central squares of Havana, is the national tree of Cuba, and the tallest palm tree is ceroxylon of Andean (Ceroxylon andicola), reaching 60 m in height, is the national emblem of Colombia.
Palms are undoubtedly an ancient family, which is also confirmed by paleobotany. Most scientists believe that palm trees have common origin with liliaceae. However, apart from some common featurescharacteristic of monocots, palms, at least with modern liliaceae, have little in common. Important features palms, like the next family, - a tendency to aggregation of flowers into complex inflorescences and complete absence boxes. In any case, the position of palms in the system is rather isolated.
The seed is a plant propagation organ that develops from the ovule after fertilization.
During the formation of a seed and a fetus, one of the sperm fuses with the egg, forming a diploid zygote (fertilized egg). Subsequently, the zygote divides many times, and as a result, a multicellular plant embryo develops. The central cell, fused with the second sperm, also divides many times, but the second embryo does not arise. A special tissue is formed - endosperm. The endosperm cells accumulate reserves of nutrients necessary for the development of the embryo. The ovule covers grow and turn into a seed coat.
Thus, as a result of double fertilization, a seed is formed, which consists of an embryo, storage tissue (endosperm) and seed coat. From the wall of the ovary, the wall of the fetus is formed, called the pericarp.
Seed types
1.with endosperm (the seed consists of three parts: seed coat, endosperm and embryo. Seed with endosperm is inherent in monocotyledons, but can also occur in dicotyledons - poppy, solanaceous, umbrella);
2. with endosperm and perisperm (usually a rare type of structure, when the seed contains the embryo, endosperm and perisperm. It is characteristic of lotus, nutmeg);
3. with perisperm (the endosperm is completely consumed for the formation of the embryo. Seeds of this type are characteristic of cloves);
- without endosperm and perisperm (the embryo occupies the entire cavity of the embryo sac, and reserve nutrients accumulate in the cotyledons of the embryo. Together, the seed consists of two parts: the seed coat and the embryo. This structure of the seed is characteristic of legumes, pumpkin seeds, rosaceae, walnut, beech, etc.)
Perisperm - The storage diploid tissue of the semen, in which nutrients are deposited. Arises from nucellus.
Endosperm - Large-cell storage tissue, the main source of nutrition for the developing embryo. First, it actively transfers substances from the mother's body to the embryo, and then serves as a reservoir for storing nutrients.
Figure: Seeds
16. Classification of fruits. Fertility .
The fruit is the reproductive organ of angiosperms, formed from one flower and serving for the formation, protection and distribution of the seeds contained in it. Many fruits are valuable food products, raw materials for obtaining medicinal, dyes, etc.
Fruit classification
In most classifications, fruits are usually divided into real(formed from an overgrown ovary) and false(other bodies also participate in their formation).
Real fruits are divided into simple (formed from one pistil) and complex (arising from the polynomial apocarpous gynoecium).
Simple ones are divided according to the consistency of the pericarp into dry and juicy.
Among the dry are distinguished single-seeded (for example, weevil, nut) and polyseeds... Multi-seeded fruits are divided into opening (bean, capsule, sac, pod, etc.) and non-opening. Non-opening dry polyspermous fruits are divided into articulated (articulated pod, articulated pod) and fractional (crocodile, two-winged fruit, etc.)
Among juicy fruits, they also distinguish polyspermous (pumpkin, apple, berry) and single-seeded (drupe).
Complex ones are called based on the names of simple fruits (polystyanka, manynuts, etc.).
Unlike the fruit (simple or complex), the seed is not formed from one flower, but from the whole inflorescence or its parts. In any case, in addition to flowers, the axes of the inflorescence take part in the formation of the seed. Infertility is a product of modification (after fertilization) not only of the flowers, but also of the axes of the inflorescence. In typical cases, the fruit mimics the fruit and corresponds to it functionally. A classic example is pineapple fruit.
17, Vegetative propagation of plants and its biological meaning Vegetative propagation of plants(from lat. vegetativas - vegetable) is the reproduction of plants using vegetative organs (root, stem, leaf) or parts thereof. Vegetative propagation of plants is based on the phenomenon of regeneration. During this method of reproduction, all properties and hereditary qualities in the daughter individuals are fully preserved.
Distinguish between natural and artificial vegetative propagation.Natural reproduction occurs constantly in nature through impossibility or difficulty seed reproduction... It is based on the separation from the mother plant of viable vegetative organs or parts that, as a result of regeneration, are able to restore the whole plant from its part. The entire set of individuals obtained in this way has the name clone. Clone(from the Greek clon - sprout, branch) - a population of cells or individuals, which is formed as a result of asexual division from one cell or individual. Vegetative propagation of plants in nature carried out by:
Separation (unicellular);
Root shoots (cherry, apple, raspberry, blackberry, rosehip);
Korenebulbs (orchid, dahlias);
Layers (currants, gooseberries);
Mustache (strawberry, creeping buttercup);
Rhizomes (wheatgrass, reed);
Tubers (potatoes);
Bulbs (tulip, onion, garlic);
Brood buds on the leaves (briofilum).
The biological significance of vegetative reproduction:a) one of the devices for the formation of descendants where there is no favorable conditions for sexual reproduction; b) the genotype of the parental form is repeated in the offspring, which is important for the preservation of the characteristics of the variety; c) one of the ways to preserve valuable varietal traits and properties; d) during vegetative propagation, the plant can be stored under conditions of impossibility of seed reproduction; e) preferred breeding method ornamental plants; f) when grafted, resistance to external conditions increases in the scion plant. It should be noted that vegetative reproduction is also disadvantageous: a) negative traits are transmitted; b) diseases of the mother's body are transmitted.
18. Unsexual reproduction, its role and forms Reproduction is a universal property of all living organisms, the ability to reproduce their own kind. With its help, species and life in general are preserved in time. The life of the cells is much shorter than the life of the organism itself, therefore its existence is supported only by the reproduction of cells. There are two ways of reproduction - asexual and sexual. During asexual reproduction, mitosis is the main cellular mechanism providing an increase in the number of cells. The parent is one individual. The offspring is an exact genetic copy of the parent material. 1) Biological role asexual reproduction Maintaining fitness enhances the importance of stabilizing natural selection; provides fast breeding rates; used in practical breeding. 2) Forms of asexual reproduction The following forms of asexual reproduction are distinguished in unicellular organisms: division, endogony, schizogony and budding, sporulation. Division is typical for amoeba, ciliates, flagellates. First, mitotic division of the nucleus occurs, then the cytoplasm is divided in half by an ever deepening constriction. In this case, daughter cells receive approximately the same amount of cytoplasm and organelles. Endogony (internal budding) is characteristic of Toxoplasma. With the formation of two daughter individuals, the mother gives only two offspring. But there may be internal multiple budding, which will lead to schizogony. Occurs in sporozoa (malarial plasmodium), etc. There is multiple division of the nucleus without cytokinesis. A lot of daughter cells are formed from one cell. Budding (in bacteria, yeasts, etc.). In this case, a small tubercle containing a daughter nucleus (nucleoid) is initially formed on the mother's cell. The bud grows, reaches the size of the mother, and then separates from her. Spore formation (in higher spore plants: mosses, ferns, moss, horsetails, algae). The daughter organism develops from specialized cells - spores containing a haploid set of chromosomes. 3) Vegetative reproduction It is characteristic of multicellular organisms. In this case, a new organism is formed from a group of cells separated from the mother's organism. Plants reproduce by tubers, rhizomes, bulbs, root tubers, root crops, root shoots, cuttings, cuttings, brood buds, leaves. In animals, vegetative reproduction occurs in the most low-organized forms. The ciliary worms are divided into two parts, and in each of them the missing organs are restored due to disordered cell division. Annelids can regenerate an entire organism from one segment. This type of division underlies regeneration - the restoration of lost tissues and body parts (in annelids, lizards, salamanders)
19 Sexual reproduction - associated with the fusion of specialized germ cells - gametes with the formation of a zygote. Gametes can be the same and different morphologically. Isogamy - the fusion of identical gametes; heterogamy - the fusion of gametes of different sizes; oogamy is the fusion of a motile sperm with a large, immobile egg.
For some groups of plants, alternation of generations is characteristic, in which the sexual generation produces germ cells (gametophyte), and the non-sexual generation produces spores (sporophyte).
Fertilization - this is the union of the nuclei of male and female germ cells - gametes, leading to the formation of a zygote and the subsequent development of a new (daughter) organism from it.
Gamete - This is a reproductive cell that has a single (or haploid) set of chromosomes, participating in sexual reproduction. That is, in other words, the egg and sperm are gametes with a set of 23 chromosomes each.
Zygote Is the result of the fusion of two gametes. That is, a zygote is formed as a result of the fusion of a female egg and a male sperm. As a consequence, it develops into an individual (in our case, into a person) with the hereditary characteristics of both parent organisms.
Isogamy
If merging gametes do not differ morphologically from each other in size, structure and chromosomal set, then they are called isogametes, or asexual gametes. Such gametes are mobile, can carry flagella or be amoeba-like. Isogamy is typical of many algae.