On the female seed scale. Department of gymnosperms
The first seed plants were now extinct seed ferns, they gave rise to gymnosperms. Gymnosperms are ancient seed plants on the path of biological progress. They appeared on Earth over 350 million years ago, long before the emergence of angiosperms. Scientists believe that the gymnosperms originated from ancient heterosporous seed ferns that have not survived to this day. Imprints of seed ferns are found in the deep layers of the earth's crust.
The structure of a pine branch
pine branch
The structure of a female pine cone
In spring, small reddish cones can be seen on the tops of young shoots. These are female cones. The female cone consists of an axis, or rod, on which the scales are located. On the scales of female cones, they are not protected by anything, like naked (hence the name - gymnosperms), lie ovules, in each of them an egg is formed.
Structure female cones pines
The structure of a male pine cone
On the same branches on which the females are located, there are also male cones. They are not located at the top of the young shoot, but at their base. The male cones are small, oval, yellow and in tight clusters.
The structure of a male pine cone
Each male bump consists of an axis on which scales are also located. On the underside of each scale there are two pollen sacs in which pollen ripens - a collection of dust particles in which male sex cells - sperm cells - are later formed.
The structure of a mature pine cone
Fertilization in pine occurs a year after pollen hits female cones. And the seeds spill out after another six months, at the end of winter. By this time, a mature female cone becomes brown and reaches 4-6 cm.
The structure of a mature pine cone
When the scales of a mature female cone move apart, it becomes clear that the seeds lie in pairs on the upper side of the scales, at their base. Seeds lie, open, bare. Each pine seed is equipped with a transparent membranous wing, which ensures its transfer by the wind.
The process of pollination and fertilization in pine. (development cycle)
Reproduction: sexual - by seeds.
Reproduction is carried out in two stages: the process of pollination and the process of fertilization.
pollination process
- The pollen is deposited on the ovules of the female cone.
- Pollen enters the ovule through the pollen inlet.
- The scales close and stick together with resin.
- Preparation for fertilization.
- Pollen, germinating, forms spermatozoa and a pollen tube.
fertilization process
Fertilization occurs in the ovule 12 months after pollination.
- The sperm fuses with the egg to form zygote.
- Develops from a zygote germ.
- From the whole ovule - seed.
The cone grows and gradually becomes woody, its color becomes brown. The following winter, the cones open and the seeds spill out. They can remain dormant for a long time and germinate only in favorable conditions.
Pine seedlings look very peculiar when they have just emerged from the seed. These are small plants whose stalk is shorter than a match and no thicker than an ordinary sewing needle. At the top of the stalk there is a bundle of very thin cotyledon needles radiating in all directions. Pine has not one or two of them, like flowering plants, but much more - from 4 to 7.
pine seed sprout
In this way, plants belonging to the department of gymnosperms differ from all other plants in that they produce seeds. Internal fertilization, the development of the embryo inside the ovule, and the appearance of the seed are the main biological advantages of seed plants, which made it possible for them to adapt to terrestrial conditions and achieve a higher development than seedless higher plants.
| pine seed (seed germ) ↓ | |
| Pine ( mature plant, sporophyte) | |
| male bumps ↓ | female bumps ↓ |
| sporangia ↓ | ovules (cones on scales, bear sporangia) ↓ |
| meiosis (many small spores - microspores, all develop) ↓ | meiosis (4 large spores - megaspores, only one develops) ↓ |
| male growth - gametophyte (pollen grain) ↓ | female outgrowth gametophyte (endosperm with 2 archegonia) ↓ |
| pollen is carried by the wind to the ovule, germinates, forming a pollen tube ↓ | eggs (one in each archegonium) |
| 2 sperm (delivered to the egg through the pollen tube) |   |
| zygote (one sperm (n) fertilizes one egg (n)) ↓ | |
| seed (germ) |
In spring, yellow-green leaves form at the base of young shoots. male bumps. In male cones are formed pollen grains consisting of two cells vegetative and generative. The generative cell is divided into two male gametes - sperm. female cones collected 1-3 at the ends of young shoots. Each cone is an axis from which two types of scales extend: barren and seed. On each seed scale, two ovules are formed on the inside. The endosperm, which is the female gametophyte, develops in the center of the ovule. The endosperm develops from a megaspore, two archegonia are formed in its tissue. The pollen is dispersed by the wind, gets on the female cones and penetrates to the pollen entrance of the ovule. A sticky liquid is released from the pollen inlet, when it dries, the pollen is drawn into the ovule. When the dust particles fall on the female cones, the scales close and stick together with resin: at this time, the ovules are not yet ready for fertilization. About a year passes between pollination and fertilization in pine. The vegetative cell of the pollen grain grows into a pollen tube that reaches the archegonium. At the end of the pollen tube are two sperm: one of them dies, and the other merges with the egg of one of the archegoniums. An embryo develops from the formed zygote.
The life cycle of Scotch pine is dominated by sporophyte- an adult tree, including: root, trunk, branches(elongated shoots), short shoots, leaves, male and female cones.
Rod root system pine reaches a depth of 20–30 m and can enter into symbiosis with the mycelium (body) of mushrooms, for example, butter, creating mycorrhiza(mushroom root). Hyphae (mycelial outgrowths) braid the pine roots from the tips to the suction zone and penetrate inside, connecting to the conductive bundles. By absorbing organic matter from the plant, the fungus supplies water with minerals to the plant.
Trunk - a vertical lignified stem reaches a height of 30-40 m. Branches (elongated shoots) on the trunk are whorled, covered with sessile, spirally arranged brown scaly leaves and end with ovoid, cone-shaped, brown buds. In the axils of the scale-like leaflets develop short shoots, of which two leaves grow - needles. A pair of leaves of Scotch pine, 3–8 cm long, 1.5–2 mm thick, covered with a sheath at the base, functions (lives) for 3–5 years and falls off together with a shortened shoot.
Men's cones- spore-bearing spikelets (strobili), are formed in spring at the base of young elongated shoots. They are assembled on a common axis. Each individual cone is 8–12 mm long, yellow or Pink colour, consists of a short rod ( axes), on which reduced spore-bearing leaves are spirally located - microsporophylls. On the underside of the microsporophylls, there are two microsporangia. In microsporangia - pollen chambers, as a result of meiosis division of diploid cells of sporogenous tissue, haploid cells are formed. microspores. In turn, microspores divide by mitosis and form a four-celled male gametophyte – pollen. Pollen grains include vegetative, generative(antiridial) and two protalial cells. Prothalial cells are reserve cells, therefore, lagging behind in growth after some time, they give their resource to the development of generative and vegetative cells, quickly degenerate and disappear. Pollen cells are surrounded by two shells - outer, thick - exine and inner, thin - intina. In two places, the exine does not fuse with the intine, forming swellings - air bags.
Women's cones cones, 3–7 cm long, appear on the tops of elongated shoots singly or in a group of 2–3 pieces. Consist of axes, on which are spirally located coverslips and seed scales - megasporophylls(female spore-bearing leaves). On the upper side of the seed scales, at their base, there are two seed germ covered with integumentary scales. The seed germ is a megasporogenous tissue - nucellus, surrounded by integumentary tissue - integument. At the top of the seed germ, facing the axis of the cone, a hole remains in the integument - the pollen inlet ( micropyle).
In spring (May), after the pollen has matured, the microsporangia of the male cones open and the pollen is dispersed by the wind. Pollination- this is the process of getting pollen on the micropyle of seed primordia. During pollination, the scales of the female cones are wide open. Pollen is carried by air currents (wind) between the scales, sticks to a sticky liquid that is released from the micropyle. Due to the drying of the sticky liquid, the pollen is drawn through the pollen inlet to the nucellus. After pollination, the micropyle overgrows, the scales of the female cone close, and the entire cone is sealed (poured) with resin from the outside. After hitting the nucellus vegetative cell pollen sprouts into it pollen tube. generative the cell enters the vegetative cell and moves in its apical part. For the next 13 months, the pollen tube slowly grows into the nucellus, towards the future female gametophyte.
Rice. 40. Diagram of the life cycle of Scotch pine
Rice. 41. Life cycle Scotch pine
A month after pollination, one nucellus cell - archesporial cell divides meiosis, forming four haploid megaspores. Three of them die, and the fourth megaspore, the furthest from the micropyle, begins to grow. Its development in megagametophyte(female gametophyte) begins six months after pollination and requires another six months to complete its formation. During this time, the megaspore cell by mitotic division increases the number of its nuclei to about 2000 pcs. At 13 months after pollination in the megaspore, cytokinesis- division of a multinucleated cell by cell walls, which localize the nuclei in individual cells. The resulting haploid tissue is called endosperm. At 13–15 months after pollination, closer to the micropyle, two or three reduced cells form from the endosperm cells. archegonia With eggs In the middle. Endosperm with two archegonia female gametophyte(sprout).
During the formation of the female gametophyte pollen tube(vegetative cell) grows through the nucellus and endosperm, enters one of the archegonia. To this moment generative a pollen cell inside a vegetative cell (pollen tube) divides into two daughter cells - sterile(leg cell) and spermatogenic(body cell). The spermatogenic cell then divides into two sperm. The pollen tube with two sperm in the middle is completely developed male gametophyte. Having penetrated the archegonium and reached the egg, the apical part of the cell wall of the pollen tube is destroyed, the cytoplasm flows into the archegonium cavity, and one of the sperm combines with the egg, forming zygote, the other sperm dies. The process of fertilization occurs approximately 13-15 months after pollination. Usually, fertilized eggs (zygotes) of all archegonia are fertilized and begin to develop into embryos (polyembryology), however, as a rule, only one embryo is completely formed.
The next six months (6 months) after fertilization, the formation of seed from the seed germ: the zygote develops into germ, endosperm remains as a storage tissue of the seed, the integument forms seed coat with pterygoid outgrowth, nucellus is spent on development endosperm and germ. Seeds of black Scotch pine, 4-5 mm in diameter, with a membranous pterygoid outgrowth of the seed coat 12-20 mm long, fully ripen in November-December, 18-21 months after pollination. The female cones become dull gray-light brown to grey-green when ripe; open (open their scales wide) from February to April and soon fall off.
Angiosperms or flowering plants - department of higher seed plants, a feature of which is the presence flower- the organ of sexual reproduction, in which the fruit leaves (pistil), enclose the seed rudiments. Another feature of angiosperms is the formation of a seven-celled female gametophyte in the seed germ - embryo sac and the fertilization of two cells in it (an egg and a central diploid cell) - double fertilization. The department of angiosperms has more than 250 thousand plant species.
Gymnosperms are higher seed plants that do not have flowers and do not form fruits. Their seeds are located openly on inside scaly leaves that form a cone. Gymnosperms are the first truly land plants, since water is not needed for their fertilization.
The heyday of gymnosperms belongs to the Paleozoic and Mesozoic eras. In the process of evolution, gymnosperms evolved from ferns. An extinct transitional form is seed ferns. In appearance, these plants were close to ferns, but had ovules that were located directly on the leaves, which gave rise to the name of this group Seed ferns.
The dominant stage is the sporophyte.
The stem (in most) is well developed, lignified. The stem includes bark, wood and a weakly expressed pith. The conductive tissue is represented by tracheids (an evolutionarily older structure than the trachea). In the bark and wood of conifers there are resin passages - intercellular spaces filled with essential oils and resin, which are secreted by the cells lining the canal. The resin protects the plant from the penetration of microorganisms and insects. Stem branching is monopodial, i.e. the apical shoot persists throughout life. When the apical shoot is removed, the growth of the plant in height stops.
Coniferous leaves are small, scaly or needle-shaped called needles. They usually stay on the tree for 2-3 years. The needles are covered with a cuticle. The stomata are deeply embedded in the leaf tissue, which reduces the evaporation of water.
The root system is pivotal, usually pivotal. The main root is well expressed, penetrates deep into the soil. Short lateral roots often contain mycorrhiza.
Gymnosperms are adapted to life on land in many ways better than spore plants. Their reproduction is not associated with the presence of moisture, since pollen is carried by wind from the male sporophyte to the female. Fertilization takes place with the help of a pollen tube. Thanks to the development of cambium and recycled wood, many gymnosperms reach large sizes.
Male cones are located among the needles at the base of young shoots. They are formed by microsporophylls (scales) that carry 2 microsporangia (pollen sacs) in which spores develop. Male cones are greenish-yellow.
Female cones are located on the tops of other young shoots. They are brown or red-brown in color. Female cones consist of a seed scale (megasporophylls) with 2 ovules and a covering sterile scale. Ovules (ovules) - formations from which seeds develop. Are located on the surface of the seed scales openly
2 - female cone
3 - seed scales with 2 ovules (top view)
4 - covering and seed scales (bottom view)
The life cycle of conifers (on the example of pine).
Pine is a monoecious plant. In the spring, cones are formed on some of its shoots - male and female. Microsporia of male cones are filled with microsporocytes (2n), which after meiosis form 4 haploid microspores. Microspores are covered with a spore membrane and form a pollen grain, in which a male gametophyte is formed, including 1 vegetative and 1 generative cells. The spore coat forms two air sacs, which facilitates the transport of pollen by wind over long distances.
A - male cone;
B - microsporophyll (1) with microsporangia (2);
B - pollen: 3 - vegetative cell; 4 - generative cell; 5 - two air bags
After the rupture of the microsporangium wall, pollen grains are dispersed by the wind and fall on the female cones.
Megasporangium is a part of the ovule, covered with an integument (cover) and attached to the seed scales (megasporophylls) with the help of a leg.
A - female cone
a - covering scales
b - seed scales
c - ovules on the seed scales
1 - seed coat from below
2 - seed scales from above,
3 - ovule in section (inside megasporangium, inside of which are archegonia, outside covered with integument)
Megasporangium includes only one megasporocyte (2n), which after meiosis forms 4 haploid spores, three of which are reduced. The remaining megaspore forms a female gametophyte that does not leave the megasporangium. On the gametophyte, archegonia are formed that contain eggs.
Pine pollination occurs in late May - early June. Once on the ovule, the pollen grain sticks to a sticky liquid, which, evaporating, draws it into the ovule. A pollen grain germinates: a pollen tube is formed from a vegetative cell, 2 sperm cells are formed from a generative cell (by mitosis). Sperm are passively transported to the archegonium by the pollen tube. One sperm fertilizes the egg, the other dies.
The zygote formed after the fusion of germ cells gives rise to the embryo, and the ovule gives rise to the seed. The seed is made up of:
germ (2n)
seed coat (2n) - formed from the integument
The supply of nutrients - endosperm (n) - is formed from the body of the gametophyte.
The developing embryo contains a root, a stalk, several cotyledons (embryonic leaves) and buds. Pine seeds ripen by the fall of next year. Usually lignified in winter seed scales diverge, and the seeds, which have wing-shaped appendages, are carried by the wind. Once in favorable conditions, the seeds germinate, giving rise to a sporophyte - a large leafy plant.
Pine- light-loving plant, undemanding to the soil. It grows on sands, on rocks, in swamps. Depending on the place of growth, it develops mainly either the main root or the system of lateral roots. Well rooted, which helps to fix the soil. Pine growing in the forest can reach up to 40 m in height. It has a straight trunk covered with red-brown bark. A low thin trunk is found in a pine growing in a swamp. The life span of a pine tree is 350-400 years.
Spruce unlike pine, it is a shade-tolerant plant. Spruce develops a dense pyramidal crown. Its lower branches usually do not die off, but are preserved, so the spruce forests are dark. Spruce is more demanding on environmental conditions and grows on more fertile and sufficiently moist soils. Its root system is less developed than that of a pine, and is located more superficially, so strong winds can “pull out” a tree with roots. Spruce leaves - needles - needle-shaped, located singly on the shoots and remain on the tree for 7-9 years. If pine cones are 4-5 cm long, then spruce cones are 10-15 cm long and develop within one year. Reproduction in spruce occurs in the same way as in pine. Its life span is 300-500 years.
Also applies to conifers. larch. It withstands severe frosts in Siberia and Yakutia. Its needles fall off for the winter, which is the reason for its name.
Exceptional durability sequoia, or mammoth tree. The duration of her life is 3-4 thousand years.
In pine and mixed forests, on dry hills, common juniper is found - an evergreen shrub with needle-like leaves. Its peculiar cones have indehiscent scales and resemble fleshy bluish berries.
The value of conifers .
Like all green plants, they form organic matter, absorb carbon dioxide and release oxygen. Coniferous forests delay the melting of snow and enrich the soil with moisture. Pine emits phytoncides - volatile substances that have an antibacterial effect. Preserve the structure of the soil and protect it from destruction (pine).
A person uses conifers as a valuable building and ornamental material (“ship pines”, “mahogany” - sequoia wood, decay-resistant larch wood). Spruce wood is used to make paper. Turpentine, rosin, sealing wax, varnishes, alcohol, and plastics are obtained from conifers. From the seeds of the Siberian cedar pine, edible oil. Cedar pine seeds are edible. Some inhabitants of the forest feed on the seeds of conifers. Juniper cones are used as medicinal product. Many conifers are cultivated as ornamental plants
### Homework
1. Siberian pine seeds are called pine nuts. Explain whether such a name is scientifically correct.
2. Scientists have found that coniferous trees(spruce, pine) are less resistant to air pollution from industrial gases than deciduous trees. Explain the reason for this phenomenon.
· Various harmful substances settle on the leaves.
· In deciduous plants, the leaves fall off annually, and harmful substances are removed with them, coniferous plants leaves live 3-5 or more years, so harmful substances are not removed and lead to poisoning of the body.
3. Give a detailed answer to the question. What are the characteristics of coniferous plants?
4. Why in August in a coniferous forest under the trees you can see a lot of fallen needles, but in a deciduous forest there are almost no fallen leaves from last year? How does this affect soil fertility?
· The needles contain a lot of resinous substances that hinder their decomposition by microorganisms.
· In addition, in a coniferous forest under shade conditions, the temperature is lower and the rate of decomposition is low.
· Due to the slow decomposition and leaching of organic matter, the soil in the coniferous forest contains little humus.
5. What chromosome set is typical for pine pollen grain and sperm cells? Explain what initial cells are and as a result of what division these cells are formed?
6. Why do pests live more on old, diseased pine trees?
Answer:
· A lot of resin is released on young trees,
· the resin contains turpentine, which repels pests.
· Old trees are more comfortable hiding places.
7. What are the advantages of plant propagation by seeds compared to spores?
8. What is the difference between a pine seed and a fern spore and what are their similarities?