Seed coat. The structure of the seed and the phases of its development Why the seed coat remains on the seedlings

Lately I have been increasingly unpleasantly surprised by the sprouting of seedlings. I don’t know why the seed coat does not fall off the leaves of many sprouts. This phenomenon is very unpleasant, because if it is not removed, the seedlings will lag behind in development and may even die. How can I help the seeds shed their shell?

Typically, remaining seed coats indicate that the sprouts are weak. But do not rush to reject crops, since a similar phenomenon occurs with small crops. So, when sowing tomatoes, peppers and eggplants, they need to be buried only 1 cm. Deeper is undesirable, and shallower too. If you planted smaller, then many of the seed coats will not fall off after germination. Such plants can be helped to get rid of the seed coat. To do this, you need to create conditions of high humidity and strengthen the plants by watering them with Kornevin’s solution.

Advice from the "Household"

You cannot remove the peel manually, as this will inevitably damage the cotyledon leaves. Not to mention the fact that the leaf blade in the seed coat is not hardened and after opening it may suffer from sunburn.

But if the seeds are old, then there may be especially many seeds that have not been freed from the shell. There is no point in saving them, since weak sprouts will not produce a high yield. Such sprouts simply need to be removed.

Another reason for such non-standard shoots is a loose or dry substrate. It is usually loose due to the high peat content. Therefore, when preparing the mixture, add at least a third of garden or turf soil. It will give the desired density. If there is little land and peat predominates, then the sprouts, without encountering resistance, will bring the seed coat into the sun.

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The seeds of oilseed plants 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 according to 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 form interacting systems.

STORAGE FABRICS

In seeds, the main, or storage, tissues are most developed: embryonic and endosperm tissues. These tissues accumulate and store nutrients.

Oilseed plants, in the seeds of which almost all reserve substances are concentrated in the embryo, more precisely in its cotyledons, include sunflower, mustard and soybean. Thus, 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 beans, poppy seeds and sesame seeds. In the embryo of such seeds, as a rule, there are almost no reserve nutrients, and the cotyledons are poorly developed.

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

Place of deposition of reserve substances in oilseeds

Family, genus, species of plants	Fruit type	Place of deposition of reserve substances	Plant parts processed in oil refineries
Legumes
	Multi-seeded bean	Cotyledons of the embryo and endosperm
		Cotyledons embryo	Seeds and fruits
Asteraceae
Sunflower, safflower
Celery
Coriander	Two-seed	Endosperm
Brassicas
Rapeseed, mustard, rapeseed, camelina,	Pod (pod)	Cotyledons of the embryo
Malvaceae
Cotton	Box	Cotyledons of the embryo and endosperm
Hemp
		Cotyledons of the embryo
Linen
	Box	Cotyledons of the embryo and endosperm
Lamiaceae
Perilla, lallemancia		Cotyledons of the embryo
Euphorbiaceae
Castor bean	Box	Endosperm	Seeds, parts of fruits (thirds)
Sesame
Poppy

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

This division of seeds is conditional, and can only be traced in seeds in which the ripening process has completely completed.

Integumentary tissues - fruit and seed coats

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

Cover tissues ensure seed germination under conditions most favorable for seedling development. This function of integumentary tissues is determined by the specificity chemical composition, which ensures their impermeability to water and air oxygen. The impermeability of fabrics to water is explained by the fact that they contain lipids (mainly waxes and waxy compounds). Many oilseeds and seeds are covered with a thin film (coating) of wax-like compounds. The integumentary tissues of many fruits and seeds form hairs that enhance the protective functions of the tissue or promote seed dispersal. In cotton seeds, for example, epidermal hairs (cotton fiber) reach 70 mm. Sometimes a rough protective tissue - cork - is formed in the integumentary tissues. 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 are found in the seed coat and in the walls of the fruit, so removing these tissues promotes seed germination. The presence of compounds such as phenols in the integumentary tissues may also enhance impermeability. Mucilage accumulates in the seed coat of certain plants, such as flax. When in contact with water, the mucus shells swell and the seeds become sticky, which helps 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 the fall, under conditions of excess humidity, it prevents the supply of oxygen to the embryo, delaying germination until more favorable conditions occur.

If the fruit coat of mature seeds is not destroyed 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 sunflower, the seed coat is a thin film consisting of outer (fringed) tissue and inner (epidermis). If the seeds do not retain their fruit membranes after ripening, then their seed coat is usually strong, and the structure of the tissues that make it up is similar to the tissues of the fruit membrane. In some cases, the seed coat can grow together with the oil-containing tissues of the kernel (for example, in flax), and even when the seeds are destroyed, this connection is maintained. 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 integuments are more common in more evolutionarily ancient plants.

EMBRYO

The seed embryo consists of a rudimentary root, a stalk (hypocotyledon), a bud and the first leaves called cotyledons. Often the root, subcotyledon and bud are called the bud-root.

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

The ground tissue and core consist of short cylindrical cells. As a rule, these embryo tissues are more resistant to mechanical stress when crushing seeds during technological processing.

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

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

The embryo of seeds of different oilseeds retains the same type of structure, but differences are found in the degree of development, size and structure of the constituent parts, especially the cotyledons. Thus, in seeds without endosperm, for example sunflower, the cotyledons are thick and fleshy, since all the reserve lipids and proteins are concentrated in the cotyledons. In cotton, the cotyledons are thin, but their area is comparatively larger, since they are rolled into several non-joining rows. 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 rolled cotyledons, which consists of several rows of cells depending on the depth of the folds and forms a leveling layer. In intermediate type seeds (flax), the volume of the endosperm is equal to the volume of the embryo.

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

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The seed consists of three main parts: the embryo, the endosperm - a container for reserve nutrients, and the seed coat. If reserve substances are necessary to nourish the embryo during germination and development of the seedling, and the shell primarily performs the function of protecting the seed, then the embryo represents the rudiment of the future plant (Fig. 3)

Seed embryo.

After fertilization of the egg, a zygote is formed - a cell in which the rudiments of all the characteristics and properties of an adult organism are concentrated. The embryo, while developing, partially or completely uses endosperm substances for nutrition and its formation. In monocotyledons, one cotyledon is formed, and the growing point is located on the side. The main part of the cereal grain consists of endosperm. In dicotyledons, two cotyledons develop, where reserve nutrients are deposited, and the embryo fills the entire seed. Their growing 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 mother seed and are better adapted to environmental conditions.

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

Covers of the seed.

The seed coat develops from the outer covering 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 membrane appears.

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

The basis of the seed coat is fiber - a cellulose skeleton impregnated with lignin, which promotes its lignification.

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

According to the nature of the surface, the shell can be shiny, matte, smooth, cellular, prickly, equipped with flakes or other outgrowths.

In filmy grains (oats, barley, etc.), the grains remain enclosed in flower scales after threshing, which significantly reduces damage to the seeds and improves their preservation. Great value To preserve the viability of seeds, the integrity of their integument is essential. 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 effects of microorganisms.

The shell, as well as the aleurone layer, delay the flow of moisture into the seed and prevent it from getting wet during light rain, and from drying out in dry weather. Damage to the shells contributes to faster wetting and even leaching of substances from the contents of the seed, and in some cases cause untimely germination of the seed.

In leguminous grasses, 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 condition changes, the flow of moisture slows down and even so-called hard seeds are formed, the skin of which becomes waterproof. However, if the integrity of the integument is damaged, water immediately begins to flow to the internal tissues of the seed. Not the entire surface of the seed is equally accessible to water. Thus, in grain crops, moisture penetrates faster into the embryonic part of the seed, and in legumes, into the hilum zone.

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

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

Wheat Corn

Shells 8.9 7.4

Endosperm 87.9 82.5

Embryo 3.2 10.1

The reserve nutrients account for the bulk of the seed, and the larger and heavier the seeds, the more reserve nutrients they contain, and the larger the embryo. With strong integument, such seeds develop into a stronger seedling that is resistant to various unfavorable conditions, ensuring 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, there are six periods of seed development.

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

2. Formation - from formation to establishing the final grain length. The differentiation of the embryo ends, the color of the grain is green, and starch grains begin to appear. Grains contain a lot of free water and little dry matter. The weight 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 starch deposition in the endosperm until it stops. During this period, the width and thickness of the grain increases to a maximum, and the Endosperm tissue is fully formed. Grain moisture content decreases to 38-40% as dry matter accumulates. The duration of the period is on average 20-25 days.

4. Maturation - begins with the cessation of the supply of nutrients. At this time, the processes of polymerization and drying predominate. Humidity drops 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 increases. Seed moisture becomes equilibrium with relative air humidity. Breathing fades. 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 begin a new cycle of plant life, there is a slow aging of colloids, which is accompanied by weak respiration. They remain in this state until germination or 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 into two.

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

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

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

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

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

The phase of firm ripeness - the endosperm is hard, mealy or glassy at the break, the shell is dense, leathery, the color is typical, humidity 8-22%, phase duration 3-5 days. Significant changes in the sowing qualities and yield properties of seeds occur over the phases. Thus, seeds in the milky state have lower germination energy, growth vigor, and 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 with 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. Frosted grain deteriorates 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 waxy ripeness at a humidity of 35-40%. At this time, the plants can be mowed and placed in windrows.



Have you encountered a problem when seedlings were unable to shed their seed coats in a timely manner? You probably noticed that such plants looked frail and were far behind their relatives in development.

Most often, the situation is resolved by the natural death of weak plants. When I look at such dead creatures, my hands are simply itching to help them quickly get rid of their seed caps;). In the article I would like to discuss with you whether it is worth doing this? 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. This means that such plants are less promising in terms of yield.

I have often even observed 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 several more versions come to my mind as to why seedlings are unable to shed the seed coat on their own:

• the seeds are planted at too shallow a depth;
• the seeds are covered with too loose a substrate;
• the soil was not compacted after sowing;
• The film that created the optimal microclimate in the container was removed early, and the seed coat became very dry in the dry air.

Let me note that there is no need to sound the alarm ahead of time. Give your green pets a chance to cope with this task themselves.

However, if the matter has clearly stalled, then you can help the poor people 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 warm water from a pipette or syringe onto the leaves and wait until the cap softens a little. And only then try to carefully pick it off with the blunt side of the needle.

To keep the number of seedlings with stuck seed coats to a minimum, follow these 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 can easily get rid of it. Comprehensive information on 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 fairly thick layer of compacted soil. But here it is important not to overdo it and not to plant the seeds too deeply, otherwise you may be left without any seedlings at all. And one more thing: the seeds of crops such as celery and many other herbs are so small that they are sown with almost no soil. Therefore, the second tip does not apply to them.

Let's not forget that in nature there is nothing useless or superfluous, and the seed coat performs an important function up to a certain point. It supplies the plant with the nutrients 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 interfere with Mother Nature only if absolutely necessary.