Seed coat. The structure of the seed and the phases of its development New from users

The seed consists of three main parts: the embryo, the endosperm - a receptacle for reserve nutrients and the seed coat. If reserve substances are necessary for the nutrition of the embryo during germination and development of the seedling, and the shell performs mainly the functions of protecting the seed, then the embryo is the germ of the future plant, (Fig. 3)

The germ of the seed.

After fertilization of the egg, a zygote is formed - a cell in which the rudiments of all the signs and properties of an adult organism are concentrated. The embryo, developing, partially or completely uses the substances of the endosperm for nutrition and its formation. In monocotyledonous plants, one cotyledon is formed, and the growing point is on the side. The main part of the cereal grain consists of endosperm. Dicotyledons develop two cotyledons, where reserve nutrients are deposited, and the embryo fills the entire seed. Their growth point is between the cotyledons.

If the embryo has two cotyledons that are brought to the surface, then the seedlings are more likely to switch to additional autotrophic nutrition, are less dependent on the parent seed, and better adapt to environmental conditions.

Endosperm is the tissue that develops around the embryo after the fusion of gametes during fertilization. Endosperm is not only a nutrient tissue, it plays a more significant role in the formation of seeds and young plants.

Seed covers.

The seed coat develops from the outer integument of the ovule. In cereal seeds, the seed coat is closely fused with the walls of the ovary.

After fertilization, during the development of the seed, the walls of the ovary undergo morphological and biochemical changes, as a result of which the fruit coat appears.

The cover protects the internal parts of the seed from mechanical damage, harmful effects external environment and regulates the flow and return of water, gas exchange, etc.

The basis of the seed peel is fiber - a cellulose skeleton impregnated with lignin, which contributes to its lignification.

In fruits, the outer layer of the cover is the fruit coat, under the cover of which are the rest of the seed, including the seed coat. In this case, the fruit coat constitutes the most developed part of the integument of the seed, while the seed coat is significantly reduced, and many functions of the latter are transferred to the fruit coat (Fig. 4).

By the nature of the surface, the shell is shiny, matte, smooth, cellular, prickly, equipped with volutes or other outgrowths.

In filmy breads (oats, barley, etc.), grains after threshing remain enclosed in lemmas, which significantly reduces seed injury and improves their safety. The integrity of their covers is of great importance for maintaining the viability of seeds. Through cracks and other damage to the shells, many pests and microorganisms penetrate into the inner part of the seed, which significantly reduces the potential yield as a result of the destructive action of microorganisms.

The shell, as well as the aleurone layer, delay the entry of moisture into the seed and prevent it from moistening during light rain, and from drying out in dry weather. Damage to the membranes contributes to more rapid soaking and even leaching of substances from the contents of the seed, and in some cases cause untimely germination of the seed.

In legumes, lupine, and some other crops, the rate of moisture entry into the seeds is related to the palisade layer present in their skin. When its state changes, the flow of moisture slows down and even the so-called hard seeds are formed, the peel of which becomes waterproof. However, if the integrity of the covers is violated, water immediately begins to flow to the internal tissues of the seed. Not the entire surface of the seed is equally accessible to water. So, in grain crops, moisture penetrates faster into the germinal part of the seed, and in legumes - into the hilum zone.

Seed shells have the property of semi-permeability with respect to certain substances in solution. The semi-permeability of the seed coat is of great biological and economic importance. It significantly affects the behavior of seeds during dressing, when they come into contact with fertilizers, on the germination of seeds with an increased salt content in the soil, etc.

The ratio of different parts of the seed varies depending on the varietal characteristics, size, degree of maturation, etc. On average, it can be characterized by the following values, % of the grain mass:

Wheat Corn

Casings 8.9 7.4

Endosperm 87.9 82.5

Embryo 3.2 10.1

The share of reserve nutrients accounts for the bulk of the seed, and the larger and heavier the seeds, the more reserve nutrients they contain, and the larger their embryo. With strong covers from such seeds, a stronger and more resistant to various adverse conditions seedlings develop, providing increased plant productivity.

Periods and phases of seed development.

From the moment of fertilization to full maturity, a number of complex transformations are observed in the seed, i.e. its development takes place. In wheat, six periods of seed development are distinguished.

1. Education - from fertilization to the formation of a growth point. The seed has been formed, i.e. when separated from the plant, it is capable of producing a viable sprout. The mass of 1000 seeds is 1 g. The duration of the period is 7-9 days.

2. Formation - from formation to the establishment of the final length of the grain. The differentiation of the embryo ends, the color of the grain is green, starch grains begin to appear. The grains contain a lot of free water and little dry matter. The mass of 1000 seeds is 8-12 g. The main thing during this period is not the accumulation of reserve substances, but the formation of all parts of the grain. The duration of the period is 5-8 days.

3. Filling - from the beginning of the deposition of starch in the endosperm until it stops. During this period, the width and thickness of the grain increases to a maximum, the endosperm tissue is fully formed. Grain moisture content drops to 38-40% as dry matter accumulates. The duration of the period is on average 20-25 days.

4. Ripening - begins with the cessation of the supply of nutrients. At this time, the processes of polymerization and drying predominate. Humidity is reduced to 18-12%. The grain is ripe and suitable for technical use, but the development of the seed is not yet complete, physiological processes are taking place in it.

5. During post-harvest ripening, the synthesis of high-molecular protein compounds ends, free fatty acids are converted into fats, the activity of enzymes decreases, and the air and water resistance of the seed coats increase. The moisture content of the seeds becomes equilibrium with the relative humidity of the air. The breath is fading. At the beginning of the period, seed germination is low, and at the end it becomes normal. The duration of the period depends on the characteristics of the culture and external conditions.

6. Full ripeness - begins from the moment of full germination, the seeds are ready to start a new cycle of plant life, colloids are slowly aging, which is accompanied by weak respiration. In this state, they are until germination or until complete death due to aging during long-term storage.

The periods are divided into smaller stages of seed development - phases. The filling period is divided into four phases, and the ripening period is divided into two.

The watery phase is the beginning of the formation of endosperm cells. The grain is filled with a watery liquid, its moisture content is 80-75%, free water is 5-6 times more than bound water. Dry matter is 2-3% of the maximum. The duration of the phase is 6 days.

The pre-milk phase - the contents are watery with a milky tint, since starch is deposited in the endosperm, the shell is greenish, the humidity is 75-70%, the dry matter is 10%. The duration of the phase is 6-7 days.

Milk phase - the grain contains a milky white liquid. Its humidity is up to 50%; dry matter accumulated 50% of the mass of mature seed. The duration of the phase is from 10 to 15 days.

Pasty phase - the endosperm has the consistency of dough. Chlorophyll is destroyed and remains only in the groove. Humidity is reduced to 42%, dry matter accumulated 85-90%, the duration of the phase is 4-5 days.

The phase of wax ripeness - the endosperm is waxy, elastic, the shells are yellow, the humidity decreases to 30%, the growth of dry matter stops. The duration of the phase is 3-6 days.

The phase of hard ripeness - the endosperm is hard, powdery or glassy at the break, the shell is dense, leathery, the color is typical, humidity is 8-22%, the duration of the phase is 3-5 days. By phases, significant changes in sowing qualities and yield properties of seeds occur. Thus, milky seeds have lower germination energy, growth vigor, field germination and are inferior in productivity to seeds in waxy and hard ripeness.

Seeds often have reduced yield properties, have a long post-harvest ripening period, and are poorly stored. High temperature at normal humidity reduces filling and accelerates biochemical processes. In this case, the seeds are formed of high quality.

Spring frosts have a negative effect on grain seeds at the beginning of wax ripeness. Frost grain spoils much more during storage and produces a high percentage of abnormal, weakened sprouts.

The accumulation of dry matter in the grain ends in the middle of wax ripeness at a moisture content of 35-40%. At this time, the plants can be mowed and laid in windrows.

Oilseeds are complex multicellular formations built from several types of tissues. Tissue is a collection of cells that perform a specific function in the plant body and are similar in structure. Seed tissues are differentiated in terms of physiological and biochemical properties, the nature of metabolic processes and chemical composition. Tissues of the same name from different plants usually have great similarities and perform similar functions. As a rule, tissues are not isolated from each other and constitute interacting systems.

STORAGE FABRICS

Seeds have the most developed basic, or storage, tissues: tissues of the embryo and endosperm. In these tissues, the accumulation and storage of nutrients occurs.

Oil plants, in the seeds of which almost all reserve substances are concentrated in the embryo, more precisely in its cotyledons, include sunflower, mustard and soybeans. So, in sunflower, the endosperm is presented in the form of a thin single-row tissue fused with the seed coat.

Plants whose seeds have a well-developed endosperm include castor bean, poppy, and sesame. In the embryo of such seeds, as a rule, there are almost no reserve nutrients, and the cotyledons are poorly developed.

In some cultures, the reserve substances in the seeds are distributed relatively evenly - both in the cotyledons and in the endosperm. Both tissues are well developed. These plants include flax (table).

Place of deposition of reserve substances in oilseeds

Depending on the degree of development of the endosperm, the seeds are divided into three groups - without endosperm, with endosperm and with a uniformly developed embryo and endosperm.

Such a division of seeds is conditional, and it can be traced only in seeds in which the maturation process has completely ended.

COVERING TISSUES - FRUIT AND SEED SHELLS

Integumentary tissues protect the embryo and endosperm of seeds from adverse external influences - mechanical damage, drying out, overheating, hypothermia, radiant energy, penetration of foreign organisms, and excessive moisture. The performance of the protective function leaves a specific imprint on the structure of integumentary tissues, primarily the outer shells of seeds - fruit and seed. These shells in most plants consist of powerful and hard fibrous tissue, composed of elongated thick-walled cells, usually dead, devoid of intracellular content. Because of the characteristic arrangement of the cells and their shape, the tissue is sometimes referred to as a palisade.

Integumentary tissues ensure the germination of seeds under conditions most favorable for the development of the seedling. This function of integumentary tissues is due to the specificity chemical composition, which ensures their impermeability to water and air oxygen. The impermeability of tissues to water is explained by the fact that they contain lipids (mainly waxes and wax-like compounds). Many oil-bearing fruits and seeds are covered with a thin film (plaque) of wax-like compounds. The integumentary tissues of many fruits and seeds form hairs that enhance protective functions tissues or promote seed dispersal. In cotton seeds, for example, epidermal hairs (cotton fiber) reach 70 mm. Sometimes a rough protective tissue is formed in the integumentary tissues - cork. The cells of this strong and elastic tissue die off and consist only of thick walls that surround cavities filled with air or resinous substances.

Germination inhibitors were found in the seed coat and in the walls of the fruit, so the removal of these tissues promotes seed germination. The presence of compounds such as phenols in the integumentary tissues may also enhance the impermeability. In the seed coat of individual plants, such as flax, mucus accumulates. When in contact with water, the mucus membranes swell and the seeds become sticky, which helps to keep the seeds on the soil and prevents them from being washed away and carried away by rain or wind. The swollen layer of mucus is impermeable to oxygen, and in autumn, under conditions of excessive humidity, it prevents the supply of oxygen to the embryo, delaying germination until more favorable conditions occur.

If in mature seeds the fruit coat does not collapse during ripening and harvesting, then the seed coat has a structure similar to the structure of the main tissue - the embryo or endosperm. For example, in a sunflower, the seed coat is a thin film consisting of an outer (fringed) tissue and an inner (epidermis). If seeds do not retain fruit coats after ripening, then their seed coat is, as a rule, strong, and the structure of the tissues that make it up is similar to the tissues of the fruit coat. In some cases, the seed coat can grow together with the oil-containing tissues of the nucleus (for example, in flax), and even when the seeds are destroyed, this connection is preserved. More often, the seed coat only comes into contact with the kernel (in soybeans, mustard, cotton, castor beans).

Most processed oilseeds have a dry seed coat. Seeds with succulent covers are more common in more evolutionarily ancient plants.

GEM

The embryo of the seed consists of the root, the stalk (subcotyledonous knee), the bud, and the first leaves, called cotyledons, which are in their infancy. Often the root, hypocotyl knee and kidney are called root-kidney.

The most important tissues of the root-kidney include external tissues - the epidermis, storage tissue, core, procambial cords, which are conductive and mechanical tissue.

The main tissue and core are composed of short cylindrical cells. As a rule, these embryonic tissues are more resistant to mechanical stress during seed grinding during technological processing.

The cotyledons consist mainly of two types of tissues - integumentary (outer and inner epidermis) and main (spongy and palisade). In the thickness of the cotyledon there are conductive and mechanical tissues from which the leaf veins are formed. The external tissues of the embryo are single-row, their protective functions are manifested insignificantly. The main tissue is multi-rowed and consists of cells somewhat elongated in the radial direction.

The root-kidney is usually located at the sharp end of the seed between the cotyledons.

The embryo of the seeds of different oilseeds retains the same type of structure plan, but differences are found in the degree of development, size and structure of the constituent parts, primarily cotyledons. So, in seeds without endosperm, for example, in sunflower, the cotyledons are thick, fleshy, since all the reserve lipids and proteins are concentrated in the cotyledons. In cotton, the cotyledons are thin, but their area is relatively larger, since they are folded into several rows that do not grow together. In seeds with a well-developed endosperm, such as castor beans, the cotyledons consist of two thin leaves separated by an air cavity.

ENDOSPERM

The endosperm consists of tissue similar in structure to the main tissue of the embryo. In seeds without endosperm, this tissue is practically absent; it is represented by one or two rows of cells, partially fused with the seed coat.

In cotton seeds, the endosperm is a tissue that fills the folds of folded cotyledons, which consists of several rows of cells, depending on the depth of the folds, and forms a leveling layer. In seeds of the intermediate type (flax), the volume of the endosperm is equal to the volume of the embryo.

In seeds with a developed endosperm (castor beans), the endosperm is the main storage tissue, which occupies almost all the free space inside the seed coat.

In the groove, the seed coat and the pigment band join together to form a common sheath around the endosperm and embryo. When the grain ripens, both parts of this shell are filled with an oily substance or a cork-type substance.

Most researchers believe that this is a cork-type substance.

The pigment layer is filled with pigment only in red grain wheats. According to Kraus, around the cork substance of each cell there is a skin-like layer and an outer lignified layer. The latter is also mentioned in the works of Bradbury et al.

The seed coats of the Poonia and Trubile wheats have been studied in some detail; in their structure and in their composition, they are completely similar. The seed coat is firmly connected to either the transverse or tubular cells on the outside and the nucellar epidermis on the inside. Three layers can be distinguished in the seed coat: a thick outer cuticle, a "colour layer" containing pigment, and a very thin inner cuticle. However, the last layer may in some places be so closely connected with the color layer that it becomes indistinguishable. A fourth was found in Trubile wheat, especially thin layer hyaline substance; it is believed that it was formed from the swollen outer pectin-containing cell walls of the outer layer of the seed coat. A similar layer was also observed in Poonia wheat, where, on histochemical analysis, it was positive for pectin and fiber content. The hyaline layer (soluble in sulfuric acid) is located between the outer cuticle and the colored layer.

Both cuticles test positive for suberin or cutin. More extensive microchemical analyzes indicate that the seed coat is cutinized.

The color layer in Poonia wheat, in contrast to this layer in Troubile wheat, gives a weak positive reaction when analyzed for tannins. In a grain of wheat, the color layer consists of two layers of cells that change and shrink as the grain matures. The cells of these two layers intersect each other at an angle of less than 45°. According to Percival, these cells are 100-150 in size; according to Vogl, their width does not exceed 9-12 c.

The seed coat of white grain wheat is different from the seed coat of red grain wheat. In white-grain wheat, both compressed layers of cells that make up the central part of the seed coat consist of fiber and are not corky. They contain almost no or very little pigment, depending on the variety. Only the cells located in the groove have some scattered bast inclusions. When the seed coat is treated with sulfuric acid, the cells of these two layers dissolve and two films remain: an outer cuticle, which resembles that of red wheat, and a thin inner film, which has no structure.

Both the outer cuticle and the seed coat as a whole have different thicknesses in different parts of the grain. The outer layer of the seed coat has the greatest thickness in the groove, on the top of the grain (at its sharp end) and in the area from the seed entrance to the base of the groove, and the smallest - above the embryo. The thickness of the outer cuticle (erroneously described as the seed coat) in Pacific Northwest wheat is 1.5-3.5. In Poonia wheat, the average thickness of the outer cuticle is 2-4 and the thickness of the seed coat is about 5-8. The outer cuticle, like the entire seed coat, is thicker near the pigment margin in the groove, at the top of the grain, and at the base of the grain near the bottom of the embryo. In the region of the seminal entrance, above the protruding basal part of the embryo, the seed coat of red wheat is so modified that water and microorganisms can easily penetrate into the grain through it. In addition, mold and moisture can find access to the seed entry space through the spongy parenchymal tissue of the pericarp at the site of grain attachment to the mother plant. The structure of the seed coat in the region of the seminal inlet has been studied in detail in red and white wheat.

Adhering to the classification of field crops by P. I. Podgorny (1963), we will consider the structure of the seeds of the most important crops according to the following subgroups: typical breads, millet And other cereals.

I. typical bread. This group includes the so-called group I breads, the seeds of which germinate with several roots: wheat, rye, barley and oats. Characteristic for seeds of this group - the presence of a groove.

cereal fruit – grains , have significant morphological differences. Some species have free grains (naked), others - membranous, while the films either grow together with the grain, or freely envelop it. The lemmas of membranous cereals have a great variety in morphology, especially in wild and weed plants.

In grains, they distinguish base , that is, that part of the fetus where the embryo is located, and peak - part opposite to the base (Fig. 1). The top often has hairs that form the so-called tuft (except for durum wheat and barley). The side on which the embryo is located is called backrest, and the opposite side belly. On the abdomen is groove, which in membranous breads is closed by the inner lemma.

groove, that is, the place of adhesion of the walls of the carpels, lies along the caryopsis, in the middle of the abdomen. Its cross section is characteristic of different varieties and, in combination with other features, makes it possible to determine the species, and in some cases the variety.

Rice. Fig. 1. Morphology and size characteristics of wheat kernels: A – view from the side of the embryo; B - view from the side of the back: 1 - crest; 2 - dorsal side; 3 - embryo; 4 - ventral side; 5 - groove; a - grain length; c - grain width.

As a typical representative of this group of cultures, let us consider in more detail the structure grains of wheat . According to morphological features, wheat grains are usually naked, less often membranous (spelt), not fused with flowering scales, oblong, the surface of the grain is smooth, the groove is wide, there is a tuft (sometimes faintly visible), the color is white, amber-yellow, brown-red and other colors .

The anatomy of seeds of grain crops has been studied most fully, although some questions remain completely unresolved to this day.

Figure 2 shows the longitudinal and transverse sections of the wheat grain, as well as the tissues that are involved in the construction of the grain and the germ.

A grain of wheat as a fruit has its own seed and a fruit coat (pericarp or pericarp), which was formed from the walls of the ovary and, probably, closely fused with the outer cover of the seed, although this is now being questioned.

The seed is made up of seed coat , germ And endosperm .

Fruit shell form several heterogeneous tissues. The fruit is covered by a single-layered epidermis, the outer cells of which are cutinized. Some cells of the epidermis at the top of the caryopsis form single-celled hairs called a tuft.

Rice. 2. Wheat grain: A – grain shape: a - elongated; b - ovoid; c - oval; g - barrel-shaped. B – longitudinal section of grain: a - epidermis; b – longitudinal layer of cells; c - layer of transverse cells (chlorophyll-bearing); d - tubular layer (cuticular); e - hyaline layer; f – aleurone layer; g - endosperm; (h) destroyed endosperm cells. germ: 1 - epithelium; 2 - shield; 3 - ligula; 4 - coleoptile; 5 - the first sheet; 6 - point of growth; 7 - provascular cords going to the scutellum, the first leaf and to the central root; 8 - epiblast; 9 - roots; 10 - coleorhiza. IN- cross section of a grain (the designations are the same). G- the structure of the shells (the designations are the same): a, b, c, d - fruit shell; seed coat - PS - transparent waterproof layer; CS - brown layer.

Under the epidermis is a parenchyma, consisting of three to four layers of thick-walled, elongated cells. Next comes a clearly expressed layer of transverse cells, the walls of which are quite thick and porous - this is the chlorophyll-bearing layer. In its cells in green seeds, chlorophyll grains are concentrated, which are destroyed as the seed ripens. The cells of this layer are peculiar in form and can be used to distinguish wheat from other crops. Even deeper, on the border with the seed coat, there is a layer of tubular cells located along the grain, but sometimes they are somewhat reformed (flattened), and this layer is not always noticeable.

The total thickness of the entire fruit shell is about 44 µ - this is the average value for many varieties of winter wheat. Fruit shells in wheat grain by weight range from 3.3 to 5.3%.

The thickness of the fruit shell depends on environmental conditions - in humid and cool places, the pericarp develops more powerful than in dry and hot areas.

Near the groove, the pericarp consists of several layers of thickened cells with slit-like pores in them. The vascular bundle is also located here and part of the nucellar tissue is preserved. At the bottom of the groove there are stomata, the role of which has not yet been clarified. Undoubtedly, the groove zone is of particular importance in the process of seed germination.

Origin seed coat other than fruit: it was formed from the remains of the internal integument and the epidermis of the nucellus.

The seed coat includes two layers - the upper colorless, consisting of strongly cutinized cells (they formed from the outer layer of the inner integument), and the lower layer, built from cells with brown pigment (in the past it was the inner layer of the integument); this layer is often referred to as brown. The nature of the color of the grain is determined by the seed coat, the cells of which contain pigments. The second layer is sometimes found with great difficulty. The thickness of the seed coat varies less than that of the fruit coat, and in winter wheat varieties it does not exceed 4.0 µ.

Under the seed coat is a rather thick structureless shiny layer called hyaline, it was formed from the cells of the epidermis of the nucellus, here you can sometimes find the remains of cellular voids. By origin, this layer is the perisperm. The hyaline layer is of particular interest, since it does not allow water to pass into the endosperm and thereby protects reserve nutrients from premature spoilage if the grain is accidentally moistened. The thickness of this layer is 4.7 µ. Although specific gravity perisperm in the overall balance of reserve nutrients is insignificant, but it plays important role. According to some reports, it is this layer that is the membrane that regulates the flow of dissolved salts into the grain.

hyaline layer almost completely fuses with external cells aleurone layer. The latter consists of one row of thick-walled uniform cubic cells (there can be two rows only in the region of the groove), filled with numerous aleurone grains. These cells contain many vitamins (B 1 , D), fat and fiber. Layer thickness approx. 42 µ.

The entire central part of the grain is occupied endosperm, consisting of thin-walled polyhedral cells filled with starch. Starch grains are represented by two forms: small, round (chondriosome) and large (plastid). Different types and even varieties of wheat have different types of starch grains and all sorts of combinations of them, and therefore can serve as a diagnostic indicator for cultivar recognition. Between the cells with starch, the endosperm also contains protein. On the shape of starch grains, except hereditary factors are strongly influenced by growing conditions. Low temperatures favor the formation of faceted grains.

There is a relationship between the texture of grains and the shape of starchy grains: in vitreous grains large elliptical grains predominate, while farinaceous- also large grains, but rounded. The nature of vitreousness lies in the fact that large layers of protein are formed between the starch grains. Thus, the anatomical structure determines the consistency of the grain.

wheat germ on the outside of the caryopsis (this is the front, or abdominal part) is covered with one row of flattened cells of the aleurone layer. The wheat germ consists of a shield with a ligula, an apiblast, a kidney covered with a coleoptile, a central and two pairs of lateral roots (and in durum wheat - one pair).

Shield, according to most researchers, is a modified cotyledon. The parenchyma of the shield consists of cells, the membranes of which have pores. In the middle of the shield, a provascular cord passes, joining at the base of the kidney to the vascular bundle of the central germinal root. Of these, conductive bundles are later formed. The lower part of the shield is directly connected to the fabric of the coleorhiza. From the side of the endosperm, the shield is covered with epithelium, that is, a layer of cylindrical cells that perform a secretory function: they secrete enzymes during seed germination, under the action of which reserve nutrients are converted into simpler compounds.

In the upper part of the shield forms a protrusion ( ligulu), covering the kidney, and on the opposite side of the embryo there is an epiblast. epiblast absorbs water during the germination of the grain and transfers it to the vascular system.

Gemmule consists of a growth point and three embryonic leaflets, of which two are developed, and the third is presented only in the form of an arcuate roller.

Outside, the kidney is covered with coleoptile, which protects it from various damages during germination.

In the zone of the coleoptilary node, in addition to the central root, there are two more pairs of accessory roots, all of which have sheaths formed by a special meristem tissue - calyptrogen. The outer layer of the central root consists of a single layer of cells, the so-called dermatogen, during germination it turns into an epiblema. The next tissue, the periblem, with subsequent growth turns into the primary cortex, and the pleroma tissue gives rise to the central cylinder.

The share of individual parts of the grain (in% of the weight of the whole grain) averages (according to P. Pelsenka): fruit shell overall 5.5 (including: epidermis 3.5, longitudinal cells 0.8, transverse cells 0.7 and tubular cells 0.5); seed coat overall 2.5 (including: brown layer 0.3, pigment layer 0.2, hyaline layer 2.0); aleurone layer 7,0; germ 2.5; endosperm 82.5.

The weight ratio of individual parts varies quite significantly depending on both varieties and cultivation conditions.

Such is the anatomical and morphological structure of the wheat grain. For other cultures, we note only some specific features.

3corns of rye glabrous, elongated, with a pointed base, the surface is finely wrinkled, the groove is deep, there is a tuft, the color is green, often yellow, brown or other colors.

The structure of the rye grain is very close to the structure of the wheat grain (Fig. 3).

fruit shell consists of a single layer of exocarp, the cells of which are elongated parallel to the long axis of the caryopsis (epidermis).

The mesocarp is very thin, consisting of one or two layers of cells, also elongated along the caryopsis. The transverse cells, which are the inner layer of the mesocarp, have curved edges, which is typical only for rye. Such a structure of cells leads to the formation of intercellular spaces, creates friability of the structure and determines the wrinkled nature of the grain surface. Tubular cells - endocarp - are destroyed early and are very rarely observed in a mature caryopsis.

seed coat formed from the inner integrum, it consists of two rows of very thin-walled cells - the upper row is colorless, the inner one is filled with a golden-brown substance - suberin.

The perisperm is quite well defined, but is represented by a thin layer of the hyaline layer.

germ rye located at the base of the grain. It consists of a kidney, which is surrounded by a closed cone-shaped coleoptile. The kidney has four leaflets, developed to varying degrees: one reaches the arch of the coleoptile, the second rises above the growth point of the kidney, the third looks like a roller around the growth point, and the fourth is rudimentary.

Unlike the wheat germ, the rye germ does not have an epiblast, but other organs of the embryo perform its functions.

In the axil of the coleoptile and the first leaf there is a rudimentary bud of the stems of the first order.

The number of roots in a rye germ is the same as in a wheat germ - a central one and two pairs of lateral ones. They have developed root caps and are surrounded by tissue. coleorhiza. Coleoriza passes into the shield. The hypocotyl is very short.

Cells endosperm, adjacent to the aleurone layer, are crayons and have a special composition, they form the so-called intermediate layer.

Rice. 3. Rye grain: A- general form; B- longitudinal section: 1 - shield; 2 - coleoptile; 3 - leaflets; 4 - epithelium; 5 - point of growth; 6 - roots; A- epidermis; b- longitudinal mesocarp cells; V- transverse mesocarp cells; G- seed coat, consisting of two rows; d- hyaline layer; e- aleurone layer; and– intermediate layer; h- endosperm.

Starch grains in endosperm cells are larger than in wheat.

Barley grains membranous, fused with lemmas. The naked barley has seeds without films. The shape is elongated-elliptical, pointed at both ends, the scales have longitudinal veins. The furrow is wide, there is no tuft. The grain surface is smooth or slightly wrinkled. The color of bare grains is green, brown-violet, while that of membranous grains is yellow or black.

Unlike grains of wheat and rye, grains of barley are surrounded by lemmas that adhere to the pericarp, this shell is sometimes called chaff (Fig. 4). Floral scales consist of several rows of cells with thick, dense walls.

Rice. 4. Barley grain: A- general form. B- lengthwise cut: A- flower film; b- fruit shell; V- seed coat; G- aleurone layer; d- endosperm; 1 – main seta; 2 - the base of the spine; 3 - epithelium; 4 - shield; 5-leaves; 6 - point of growth; 7 - roots; 8 - root cap. IN- the structure of the shell: 1 - fruit; 2 - seed; 3 - hyaline layer; 4 - aleurone layer; 5 - endosperm.

The pericarp is poorly developed, it includes only the remains of cells of the epicarp, mesocarp and transverse cells.

seed coat consists of two layers. Inner layer contains a mucous substance that can swell strongly.

germ has the same structure as the germ of wheat. The growth point is covered with a coleoptile sheath, it has four embryonic leaves (and sometimes a tubercle of the fifth germinal leaf is visible), develops in the same way as in rye. Tubercles of the shoot are laid in the axil of the first embryonic leaflet.

The embryo has five embryonic (and sometimes six) roots, of which three are well developed; all roots are covered by a root sheath (coleorrhiza).

Oat grains membranous, but the scales do not grow together with the caryopsis, but freely envelop it (naked oats have no films). They have an elongated, strongly narrowed shape, while in membranous they are fusiform with a strong sharpening towards the apex. The surface of the scales is smooth, and the grain itself is slightly pubescent, the groove is wide, there is a tuft. The color of bare seeds is light yellow, while membranous seeds are white, yellow, brown. The oat embryo contains all formations typical of cereals: scutellum, coleoptile with growth cone, coleorhiza with 5–6 roots, and epiblast (Fig. 5). In the sinus of the coleoptile, a bud of a lateral shoot is laid. The growth cone has two well-developed embryonic leaves that abut against the vault of the coleoptile, the third leaf is in the form of a tubercle, and the fourth is the rudiment of the tubercle. There are five roots, of which one is central, well formed, two are clearly marked, and two are in embryonic form.

The epiblast is strongly developed - its upper part reaches the lower part of the coleoptile, and the lower part is in contact with the coloriorhiza.

II. Millet bread (or bread of group II). This group includes corn, millet, rice, sorghum, chumiza.

The seeds of this group of cultures have neither a groove nor a tuft and always germinate with one root.

Corn kernels naked, rounded or faceted, sometimes pointed at the top, white, yellow, red, rarely blue, very diverse shades, depending on the color of the shell, aleurone layer and endosperm.

The endosperm of corn consists of mealy and horn-shaped parts. The mealy part is dominated by loosely arranged starch grains with large gaps between them.

Rice. 5. Oat grain: A- general view of the grain from the side of the groove and back. B- the structure of the embryo: 1 - shield; 2 - ligula; 3 - coleoptile; 4 - leaflets; 5 - epiblast; 6 - provascular bundle; 7 - primary roots; 8 - coleorhiza. IN- cross section of grain. G- the structure of the shells: A- pericarp; b– remains of perisperm; V- aleurone layer; G- a layer of cells with small grains of starch and is poor; d- endosperm.

In the horn-like part, starch grains are compacted, and the spaces between them are filled with protein, which gives a characteristic fracture - vitreous. Depending on the morphology and anatomical features of the seed endosperm, corn is usually divided into eight subspecies or groups of varieties ( convarietas), of which practical value have the following (Fig. 6):

1. flint corn ( Zea mays indurate Sturt.). The grain is rounded, compressed, uniformly colored, the surface of the grain is smooth, shiny. The endosperm is horn-shaped, transparent, and powdery only in the central part. The cells have multifaceted starch grains, and the gaps between them are filled with protein;
2. Tooth corn ( Z.m. indentata Sturt.). Caryopsis elongated prismatic, faceted. At the top of the grain there is a characteristic depression - a tooth-like fossa. The central part of the grain and the top are farinaceous, friable; the sides have a horn-shaped endosperm;
3. Corn starchy or mealy ( Z. m. Amylacea Sturt. ). The grain is large, close to siliceous in shape. The endosperm is completely mealy (sometimes there is a thin film of horn-like endosperm);
4. sweet corn ( Z. m. saccharata Korn. ). Caryopsis of variable shape, squeezed, somewhat angular. The top of the grain and its surface are wrinkled. The endosperm is completely horn-shaped with a characteristic luster when broken (vitreous);
5. popping corn ( Z. m. everta Sturt. ). The caryopsis is small, rounded, slightly compressed, sometimes pointed at the top. The top of the grain is rounded or wedge-shaped, wrinkled. Almost the entire endosperm of the caryopsis is horn-shaped, translucent, consisting of angular starch grains and protein;
6. Waxy corn ( Z. m. ceratin Kulesh. ). Grain of various shapes. By appearance it looks like a grain of flint corn, but has a matte finish. The peripheral part of the endosperm is completely opaque and looks like wax.

N. N. Kuleshov identified hybrid corn as an independent group, which is obtained by crossing flint and dent corn. This group of semi-tooth corn ( Z. m. Semidentata Kulesh. ) has a less pronounced depression at the top of the grain and a large horn-shaped endosperm.

Rice. Fig. 6. Scheme of grain structure of different groups of corn: I – starchy; II - dentate; III - siliceous; IV - bursting; V - waxy; VI - sugar; 1 - pericarp; 2 - aleurone layer; 3 - endosperm; 4 - embryo. Endosperm: A- mealy; b- horn-shaped; V- waxy; G- sugar.

germ corn is quite large. It consists of a scutellum, a kidney, and a root (Fig. 7). Unlike the embryos of other cereals, it does not contain an epiblast. A kidney and a root are attached to the shield with the middle stem part. In addition to the main root, the corn germ also has two lateral additional roots. The primary root is surrounded by a coleorhiza.

Rice. 7. The structure of the corn grain: A- general form. B- longitudinal lateral section: 1 - the rest of the stigma; 2 – nucellus residue; 3 - endosperm; 4 - columnar epithelium of the shield; 5 - pericarp; 6 - seed coats; 7 - shield; 8 - chalaza; 9 - vascular bundle; 10 - aleurone layer; 11 - embryo; A- primary root; b- spine cover; V- rudiments of leaves; G- coleoptile.

The kidney is well differentiated and consists of a growth cone and up to seven folded embryonic sheets. Protected kidney coleoptile, which has a fairly dense structure.

In the epithelial layer of the corn shield (this is not observed in other crops), folds have formed on the side of the dorsal surface of the shield, which increases its surface and contributes to a large release of enzymes.

The endosperm tissue is divided into three layers according to cell types: 1) the peripheral layer (or aleurone) consists of one row of cells with small aleurone grains and not containing starch grains. Sometimes in the cells of this layer there is a significant amount of oil in the form of the thinnest emulsion; 2) directly behind the aleurone layer is another type of tissue: two or three rows of narrow thin-walled cells containing starch and aleurone grains, called transitional. The next layers of cells are already larger in size, have large starch grains; 3) the central part of the endosperm is occupied by the third type of cells - very large, with large rounded starch grains, and thin layers of protein are located between them.

In forms with horn-like endosperm, starch in the horn-like zone densely fills the entire cell cavity.

In the basal part of the endosperm, cells have special form- they are narrow, long and have no starch. The content of these cells plays an important role in germination processes, but its composition is still not entirely clear. However, it has been established that maternal nutrients are involved in its formation, which entered the seed through the placento-chalazal zone.

The corn kernel has a special continuous semi-permeable non-cellular membrane, which is located between the aleurone layer and the pericarp. This semipermeable membrane is often referred to as the nucellar membrane, although its origin has not yet been fully elucidated. Some researchers believe that it was formed from the outer wall of cells nucellar epidermis, and others - from the internal integument. The thickness of this membrane is about 1 micron.

rice grains membranous, elongated-oval shape. The scales are dull, longitudinally ribbed, straw-yellow or brown in color. The caryopsis is white, rarely brown, ribbed; when threshed, the grain of rice falls out as a whole spikelet along with flowering and spikelet scales. The endosperm of the caryopsis is dense, horn-shaped, sometimes there is a powdery part in the center.

The whole systematics of rice is built on the morphological features of the grain. If there are a dozen grains of rice with flowering scales, then you can always determine the species, subspecies, branch, variety, varietal class, and even variety.

According to the most common classification, rice is divided into 2 subspecies depending on the length of the grain: short-grain rice, or small ( Oriza sativa ssp. Brevis Gust. ) and common rice ( O. s.Communis Gust. ).

Millet grain membranous with a smooth or glossy film surface, white, cream, gray, yellow, bronze, red, greenish or brown. Floral scales are hard, brittle. The caryopsis is small, spherical or oval, sometimes slightly flattened from the back (Fig. 8).

The morphological features of the millet grain are the leading indicators in determining varieties (complemented by the characteristics of the panicle). In addition to the color of the grain, the degree of collapse is also important, that is, the strength of the attachment of lemmas to the caryopsis.

Rice. 8. The structure of the grain of millet: A- general form. B- cross section: 1 - pericarp; 2 - aleurone layer; 3 - embryo; 4 - root cap; 5 - endosperm; 6 - primary root (pleroma is visible in the center, surrounded by periblema and epithelium). IN- the structure of the shells: A- epidermis; b, V- a layer of fibrous cells and spongy parenchyma; G- aleurone layer; d- endosperm.

Rice. 9. The structure of the buckwheat nut: I- side view, II- top view: 1 - top; 2 - face; 3 - rib; 4 - base. III- cross section: A- fruit shell; b- seed coat; V- cotyledons; G- vascular bundles; d- endosperm.

Millet grain consists of germ, mealy endosperm and shells. The outer shell is built from the cells of the epidermis, a layer of fibrous cells, from the parenchymal tissue and the inner epidermis. Cells are included in the fruit membrane epidermis, supercarp And intracarpel. Between these shells there is a thin air gap. The seed coat adjoins the aleurone layer, which consists of one row of small cells.

Sorghum grains naked or membranous, rounded or slightly ovoid, with a smooth, shiny surface of the scales. Scale coloring white, yellow, orange, brown, black; caryopsis coloration white, brown, cream, orange.

III. Other cereals (non-cereal) crops. In this group, consider the features of buckwheat seeds (Fig. 9). The fruits of its distinctly trihedral shape with flat smooth edges, the ribs are smooth (triangular nutlet). The color of the grain is marble, gray.

Buckwheat seeds (nut) have two shells: fruit And seed. The fruit coat consists of four layers: the outer epidermis, the sclerenchymal layer, which thickens at the ribs (six rows of cells) and is somewhat thinner in the middle of the face (three layers of cells), the brown-red prosenchymal layer, and a single-layer inner epidermis.

The seed coats are composed of the outer and inner epidermis, and between them is the parenchymal tissue.

The aleurone layer is very thin, adjacent to the epidermis.

Endosperm loose, mealy. Starch-bearing cells are arranged in radial rows, thin-walled, multi-layered.

The embryo in buckwheat is peculiar, it is located in the center of the fruit and has two folded pale green cotyledons.

Have you encountered a problem when the seedlings could not throw off the seed coat in a timely manner? You probably noticed that such plants looked frail and lagged far behind their relatives in development.

Most often, the situation is resolved by the natural death of weak plants. When looking at such deadlings, my hands just itch to help them quickly get rid of seed caps;). In the article I would like to discuss with you whether it is worth doing it? And if so, how to carry out the operation with minimal damage to a tiny seedling?

Seedlings that have difficulty shedding the seed coat are rightly considered weaker. So they are such plants are less promising in terms of productivity.

I often had to observe even the death of such seedlings, since the remnants of the seed completely block their growth. The most obvious cause of trouble is bad seeds.

But a few more versions come to my mind why seedlings are unable to shed their seed coat on their own:

• the seeds are planted too shallow;
• seeds are covered with too loose substrate;
• the soil was not compacted after sowing;
• the film, which creates an optimal microclimate in the container, was removed early, and the seed coat dried out in dry air.

I note that you should not sound the alarm ahead of time. Give your green pets a chance to do it themselves.

However, if the case is clearly stalled, then the poor fellows can be helped a little.

It is better not to try to remove the seed coat with your fingers - the cotyledon leaves of peppers and tomatoes are fragile and can be easily damaged by careless manipulations. Drop from a pipette or syringe onto the leaves with warm water and wait until the cap softens a little. And only then try to gently pick it off with the blunt side of the needle.

And so that seedlings with a stuck seed coat appear to a minimum, adhere to the following recommendations:

1. Before sowing, soak the seeds so that they are saturated with moisture and swell. The seed coat will become soft and pliable and the plant will easily get rid of it. Comprehensive information on the methods of pre-sowing seed treatment can be found.
2. Sow dry seeds to a depth of at least 1-1.5 centimeters, and be sure to compact the surface of the substrate. Thus, the seedlings themselves will easily throw off the interfering “clothes” when they make their way to the light through a rather thick layer of compacted soil. But here it is important not to overdo it and not to plant the seeds too deeply, otherwise you can be left without seedlings at all. And one more thing: the seeds of such crops as celery and many other herbs are so small that they are sown almost without powdering with earth. Therefore, the second advice does not apply to them.

Let's not forget that in nature there is nothing useless or superfluous, and the seed coat up to a certain point performs important function. It supplies the plant with nutrients that it needs at an early stage of growth, when the root system is still poorly developed. Therefore, carefully monitor the condition of the seedlings and intervene in the work of Mother Nature only in case of emergency.