Heterotrophs feed. Heterotrophic mode of nutrition in plants

In biology, heterotrophs are organisms that receive nutrients from prepared foods. Unlike autotrophs, heterotrophs are not able to independently form organic compounds organic substances.

general description

Examples of heterotrophs in biology are:

• animals from protozoa to humans;
• mushrooms;
• some bacteria.

The structure of heterotrophs suggests the possibility of breaking down complex organic substances into more simple connections. In single-celled organisms, organic substances are broken down in lysosomes. Multicellular animals eat food with their mouths and break it down in the gastrointestinal tract with the help of enzymes. Fungi absorb substances from external environment like plants. Organic compounds are absorbed along with water.

Kinds

According to the source of nutrition, heterotrophs are divided into two groups:

• consumers - animals that eat other organisms;
• decomposers - organisms that decompose organic remains.

According to the method of feeding (food absorption), consumers are classified as phagotrophs (holozoans). This group includes animals that eat organisms in parts. Reducers are osmotrophs and absorb organic substances from solutions. These include fungi and bacteria.

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Heterotrophs can use living and non-living organisms as food.
In this regard, the following are highlighted:

• biotrophs - feed exclusively on living creatures (herbivores and carnivores);
• saprotrophs - feed on dead plants and animals, their remains and excrement.

Biotrophs include:

Rice. 1. Biotrophs.

Saprotrophs include animals that eat corpses (hyenas, vultures, Tasmanian devils) or excrement (fly larvae), as well as fungi and bacteria that decompose organic remains.

Some living things are capable of photosynthesis, i.e. They are both autotrophs and heterotrophs at the same time. Such organisms are called mixotrophs. These include the eastern emerald elysia (mollusk), cyanobacteria, some protozoa, and insectivorous plants.

Consumers

Multicellular animals are consumers several orders of magnitude:

• first - feed on plant foods (cow, hare, most insects);
• second - feed on consumers of the first order (wolf, owl, human);
• third - eat third-order consumers, etc. (snake, hawk).

One organism can simultaneously be a consumer of the first and second or second and third order. For example, hedgehogs mainly eat insects, but will not refuse snakes and berries, i.e. Hedgehogs are simultaneously consumers of the first, second and third order.

Rice. 2. Example of a food chain.

Decomposers

Yeasts, fungi and heterotrophic bacteria are divided according to the method of nutrition into three types:

Rice. 3. Saprophyte mushrooms.

Saprophytes play an important role in the cycle of substances and are decomposers in the food chain. Thanks to decomposers, all organic remains are destroyed and turned into humus - a nutrient medium for plants.

Viruses are neither heterotrophs nor autotrophs, because have the properties of inanimate matter. They do not require nutrients to reproduce.

What have we learned?

Heterotrophs feed on ready-made organic substances, which they obtain by eating other organisms - plants, fungi, animals. Such organisms can feed on living organisms or their remains (biotrophs and saprotrophs). Most animals are consumers who eat other organisms (plants, animals). Decomposers that decompose organic remains include fungi and bacteria.

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Heterotrophic method of plant nutrition

general characteristics heterotrophic plants

Thus, heterotrophic nutrition of cells and tissues becomes common, as does photosynthesis.

The heterotrophic method of nutrition is the assimilation of both low-molecular organic compounds and high-molecular ones (proteins, fats, carbohydrates), but they must undergo processing - digestion. In plants, there are 3 types of digestion: intracellular - in the cytoplasm, vacuoles, plastids, protein bodies, spherosomes; membrane, carried out by enzymes of cell membranes; extracellular - enzymes formed in special cages, are released into the external environment and act outside cells.

Saprophytes

The mechanisms of saprophytic nutrition of plants and fungi are similar. In the plasmalemma of fungal hyphae there functions an H + -pump (hydrogen pump), with the help of which environment acid hydrolases are released. This leads to the hydrolysis of complex organic compounds, which are then absorbed by the fungus. The absorption mechanism is also associated with the operation of the H + pump in the plasmalemma. When the outer membrane zone is acidified, the dissociation of organic acids decreases and they penetrate into cells in the form of neutral molecules. This method is common in algae (diatoms that live at depths where light does not penetrate and feed on organic matter from the environment). When there is a large amount of soluble organic matter in water bodies, chlorococcal, euglena and other algae switch to heterotrophic nutrition.

In angiosperms, the saprophytic mode of nutrition is rare. These plants have little or no chlorophyll and are not capable of photosynthesis. To build their bodies, they use the rotting remains of plants and animals. Gidiophytum formicarum - a subshrub, the stem of which forms a large tuber, penetrated by numerous passages in which ants settle. The plant uses the waste products of ants as food. The tagged fly larvae were digested by the plant after a month.

Mycorrhiza is used by most plants mainly to increase the absorption of water and mineral salts.

Rafflesia feeds on the juices of the roots of tropical vines. It penetrates into the host's body with the help of haustoria, which secrete enzymes that destroy cell walls. Rafflesia spends its entire life in the body of the owner - underground. Only its flowers (diameter 1.5 m, red with the smell of rotting meat) appear on the surface of the soil.

Carnivorous plants

Currently, over 400 species of angiosperms and insectivorous plants are known. They are catching small insects and other organisms, digest and use as an additional source of nutrition. Most of them are found on nitrogen-poor swampy soils; there are epiphytic and aquatic forms. The leaves of insectivorous plants are transformed into special traps that also perform the function of photosynthesis. According to the method of catching it, plants are divided into two groups. 1) Passive fishing, prey a) sticks to the leaves, the glands of which secrete sticky mucus containing acidic polysaccharides (Biblis, rosewort), or b) falls into special traps in the form of jugs, urns, tubes, painted in bright colors and secreting a sweet aromatic secret (sarracenia, darlingtonia).

2) Active capture of insects a) gluing prey with sticky mucus and enveloping it with a leaf or hairs (butterfly, sundew), b) catching according to the trap principle - with the slamming of trapping leaves over the prey (aldrovanda, Venus flytrap), c) trapping bubbles into which insects are drawn in with water due to the vacuum maintained in them (pemphigus).

Common to all trapping devices is the attraction of insects with the help of polysaccharide mucus or fragrant secretion(nectar), secreted either by the trapping devices themselves, or by glands near the trap. Rapid movements of the hunting organs are carried out by changes in turgor in them in response to irritation of sensitive hairs caused by the movements of the insect.

Digestion.An insect caught in a trap is digested under the influence of the secretion of numerous glands. Some insectivores paralyze their prey with alkaloids contained in the secreted mucus (sundewdews secrete the alkaloid conitine, which paralyzes the insect). Sticky mucus contains many acidic polysaccharides consisting of xylose, mannose, galactose and glucuronic acid, organic acids and a number of hydrolases active in an acidic environment. Acidic mucous secretions, nitrogen- and phosphorus-containing breakdown products stimulate the work of glands that secrete acids (formic, benzoic), as well as proteases and a number of other hydrolases. The proteolytic activity of the flycatcher secretion has been studied in some detail. Secretory cells have a well-developed ER and Golgi apparatus, which produce large amounts of secretion.

Absorption of decomposition products is carried out by the same glands connected to the conductive system (after 5 minutes). The dominant role in the transport of digestive products belongs to simplast. Thus, the process of digestion in insectivorous plants is carried out fundamentally in the same way as in the stomach of animals. In both cases, acids are secreted ( HCI - in the stomach, formic acid - in insectivorous plants). The acidic reaction of digestive juice in itself promotes the digestion of animal food. The fundamental similarity of the process of acidic extracellular digestion in animals and plants was first pointed out by Darwin in his book “Insectivorous Plants.”

It is currently known that acidification of the environment in the stomach of animals occurs as a result of the functioning of the H + pump in the plasmalemma of the cells of the gastric mucosa.

Many insectivorous plants live on soils poor in mineral elements. Their root system is poorly developed, there is no mycorrhiza, so the absorption of mineral elements from caught prey is important for them great importance. From the body of the prey, insectivorous plants obtain nitrogen, phosphorus, potassium, and sulfur. Carbon contained in amino acids and other breakdown products is also involved in the metabolism of insectivorous plants. (Darwin also showed that if sundew plants are fed with pieces of meat, then after three months they are significantly superior to control plants in a number of indicators, especially reproductive ones. It has been established that bladderwort plants bloom only after receiving animal food).

As noted at the beginning of one of our articles, nutrition is energy production process and substances for cellular metabolism, including repair and cell growth. Heterotrophic organisms, or heterotrophs, are organisms that use organic carbon sources.

It would be very helpful, if you have not already done so, to read the relevant article at this stage.

Heterotroph survival directly or indirectly depends on the activity of autotrophs. Animals, fungi and most bacteria are heterotrophs. Almost all of them get energy by consuming food; This chapter will be devoted to issues related to the nutrition of heterotrophs. There are, however, some bacteria that are capable of using light energy to synthesize their own organic compounds from other organic raw materials. Such bacteria are called photoheterotrophs.

Heterotrophs receive writing in a variety of ways. However, the ways of converting food into a form convenient for absorption in many organisms are similar and consist of the following processes:

1) digestion- breakdown of large and complex molecular complexes that make up food into simpler and soluble forms;
2) suction- absorption of soluble molecules obtained as a result of digestion by body tissues;
3) assimilation- use of absorbed molecules for certain purposes.

The term holozoic is applicable mainly to wild animals, with a specialized niche digestive tract, or canal. Most animals are holozoic.

Holozoic nutrition includes the following processes.
1. Swallowing provides food capture.
2. Digestion- This is the breakdown of large organic molecules into smaller ones that are more easily soluble in water. Digestion can be divided into two stages. Mechanical digestion, or mechanical destruction of food, for example by teeth. Chemical digestion is digestion with the help of enzymes. Reactions that carry out chemical digestion are called hydrolytic. Digestion can be either extracellular (occurs outside the cell) or intracellular (occurs inside the cell).
3. Suction represents the transfer of soluble molecules obtained as a result of the breakdown of nutrients across the membrane into the corresponding tissues. These substances can enter either directly into cells, or first into the bloodstream, and only then transferred to different organs.
4. Assimilation(assimilation) is the use of absorbed molecules to provide energy or substances to all tissues and organs.
5. Selection(excretion) - evacuation of undigested food residues from the body and removal of final metabolic products.

Animals that eat plants are called herbivores. feeding on other animals- carnivores, and those who eat mixed food, i.e., both animal and plant, are omnivores. Some animals (microphages) feed on tiny particles, e.g. earthworms or filter feeding organisms such as bivalves. Others consume liquid food, such as aphids, butterflies and mosquitoes. There are animals that use relatively large particles for food, such as hydra and sea anemones, which capture prey with tentacles, or large carnivores, such as sharks.

“...all plants have the ability to dissolve protein substances... This should happen with the help of a solvent, probably consisting of an enzyme together with an acid.”

C. Darwin

Autotrophic organisms (from the Greek “autos” - self and “trophe” - food) are able to independently synthesize organic nutrients from inorganic ones, heterotrophic organisms - feed on ready-made organic substances. Autotrophs include green plants and some bacteria that use light energy during photosynthesis (phototrophs), as well as bacteria that can utilize the energy of oxidation of substances for the synthesis of organic compounds (chemosynthesis).

Thus, the heterotrophic method of nutrition of cells and tissues is as common for plants as photosynthesis, since it is inherent in any cell. At the same time, this method of plant nutrition has been extremely poorly studied. Familiarity with the physiology of plants that feed heterotrophically allows us to come closer to understanding the mechanisms of nutrition of cells, tissues and organs in the whole plant.

Whole plants or organs can assimilate both low-molecular organic compounds coming from the outside or from their own reserve funds, as well as high-molecular proteins, polysaccharides, as well as fats, which must first be converted into easily accessible and digestible compounds. The latter is achieved as a result of digestion, which is understood as the process of enzymatic breakdown of macromolecular organic compounds into products that lack species specificity and are suitable for absorption and assimilation. There are three types of digestion: intracellular, membrane and extracellular. Intracellular is the most ancient type of digestion. In plants, it occurs not only in the cytoplasm, but also in vacuoles, plastids, protein bodies, and spherosomes. Membrane digestion is carried out by enzymes localized in cell membranes, which ensures maximum coupling of digestive and transport processes. It has been well studied in the intestines of a number of animals. Membrane digestion has not been studied in plants. Extracellular digestion occurs when hydrolytic enzymes produced in special cells are released into the external environment and act outside the cells. This type of digestion is characteristic of insectivorous plants; it occurs in other cases, in particular in the endosperm of cereal grains.

Currently, fungi are classified as an independent kingdom, but many aspects of the physiology of fungi are close to the physiology of plants. Apparently, similar mechanisms underlie their heterotrophic nutrition.

In the plasmalemma of fungal hyphae and yeast cells, a H + pump functions, and the fungus releases various types of acid hydrolases into the environment. This leads to the hydrolysis of complex organic compounds in the surrounding substrate (extracellular acid digestion) and the absorption of their breakdown products.

The absorption mechanism is also associated with the operation of the H + pump in the plasmalemma. When the outer membrane zone is acidified, the dissociation of organic acids decreases and they penetrate into cells in the form of neutral molecules. Sugars and amino acids enter the hyphal cytoplasm in symport with H + ions using special lipoprotein carriers. The source of energy for the transfer of organic substances in symport with H + ions is the proton motive force, which includes both ΔpH and electric membrane potential, arising due to the operation of the H + pump in the plasmalemma (see Fig. 6.8).

Among plants, the saprophytic mode of nutrition is quite common in algae. For example, diatoms, which live at great depths where light cannot reach, feed by absorbing organic matter from the environment. With a large amount of soluble organic substances in water bodies, chlorococcal, euglena and some other algae easily switch to a heterotrophic mode of nutrition. Moreover, in this case, the transfer of sugars into cells is carried out in symport with H + ions, i.e., using the proton-motive force of the plasmalemma.

In angiosperms, the saprophytic mode of nutrition is relatively rare. Such plants have little or no chlorophyll and are not capable of photosynthesis, although photosynthetic species are also found. To build their bodies, they use the rotting remains of plants and animals. An example is Gidiophytum formicarum - a subshrub, the stem of which forms a large tuber, penetrated by numerous passages in which ants settle. This species uses ant waste products as food, which was proven using a radioactive label. Tagged fly larvae, which the ants carried into the stem cavity, were digested by the plant after a month, and radioactivity was detected in the leaves and underground parts of the plant.

Some species that do not contain chlorophyll use symbiosis with fungi to provide themselves with organic food; These are mycotrophic plants. There are especially many such species in the orchid family. In the early stages of development, all orchids enter into symbiosis with fungi, since the supply of nutrients in their seeds is not enough for the growth of the embryo. Fungal hyphae penetrating into the seeds supply the growing embryo with organic substances, as well as mineral salts from the humus. In adult orchids with a mycotrophic type of nutrition, fungal hyphae penetrate into the peripheral zone of the roots, but cannot penetrate further. Their further growth is prevented by the fungistatic action of the cells of the deep tissues of the root, as well as a layer of rather large cells with large nuclei, similar to phagocytes. These cells are able to digest fungal hyphae and assimilate released organic substances. Direct exchange between the plant and the fungus through the outer hyphal membrane is probably also possible.

Mycorrhiza is used by most plants mainly to increase the absorption of water and mineral salts.

Currently, over 400 species of angiosperms are known that catch small insects and other organisms, digest their prey and use the products of its decomposition as an additional source of nutrition. Most of them are found on nitrogen-poor marshy soils; there are epiphytic and aquatic forms.

Trap mechanisms. Leaves of insectivorous plants are transformed into special traps. Along with photosynthesis, they serve to capture prey. According to the method of catching it, insectivorous plants can be divided into two large groups.

At passive type When fishing, prey can a) stick to the leaves, the glands of which secrete sticky mucus containing acidic polysaccharides (Biblis, Rosolist), or b) fall into special traps in the form of jugs, urns, tubes, painted in bright colors and secreting a sweet aromatic secretion (Sarracenia , Heliamphora, Darlingtonia).

To actively capture insects, the following are used: 1) gluing prey with sticky mucus and enveloping it with a leaf or hairs (butterfly, sundew), 2) catching according to the trap principle - with the slamming of trapping leaves over the prey (al-drovanda, Venus flytrap), 3) trapping bubbles , into which insects are drawn in with water due to the vacuum maintained in them (pemphigus).

Common to all types of trapping devices is the attraction of insects with the help of polysaccharide mucus or aromatic secretion (nectar), secreted either by the trapping devices themselves, or by glands near the trap. Rapid movements of the hunting organs are usually carried out by changes in their turgor and are triggered by spreading action potentials in response to irritation of sensory hairs caused by the movements of the insect (see 13.6.1).

Digestion. An insect caught in a trap or stuck to the sticky surface of a leaf is digested under the action of the secretion of numerous glands (Fig. 7.1). Some insectivores paralyze their prey with alkaloids contained in the secreted mucus. Thus, the sundew secretes the alkaloid conitine, which paralyzes the insect. The sticky mucus secreted by the erect or stalked glands of insectivorous plants contains many acidic polysaccharides consisting of xylose, mannose, galactose and glucuronic acid. The acidic reaction of mucus is also ensured by the organic acids contained in it. The mucus secreted by the erect glands contains a number of hydrolases that are active in an acidic environment. For example, the butterwort contains acid amylase in its mucus.

Acidic mucous secretions, nitrogen- and phosphorus-containing decomposition products stimulate the work of sessile glands, which begin to secrete acids (formic, benzoic), as well as proteases and a number of other hydrolases. The proteolytic activity of the flycatcher secretion has been studied in some detail. Most of the proteases from its secretion belong to thiol proteases, among them carboxypeptidase, chitinolytic activity. In addition to proteases, acid phosphatase and esterase were found in the secretion, and in some species of insectivores - ribonuclease, lipase, and peroxidase.

Secretory cells of insectivorous plants have a well-developed ER and Golgi apparatus, which produce large amounts of secretion. The secretion of mucus, acids and hydrolases is active and depends on respiration. Respiratory poisons - arsenite, cyanide, and chloroform stop the secretion process and the production of secretion vesicles in the Golgi apparatus.

Absorption of decay products is carried out by the same glands connected to the conductive system, and occurs quite quickly, as was shown in the example of a flytrap using methylene blue. After 5 minutes, the dye penetrated into the cytoplasm of all cells of the head of the glands. Quantitative ultrastructural analysis showed the dominant role of symplast in the transport of digestive products in the flycatcher. From all that has been said, it follows that the process of digestion in insectivorous plants is carried out fundamentally in the same way as in the stomach of animals. In both cases, acids are secreted (HC1 - in the stomach, formic acid - in insectivorous plants). The acidic reaction of digestive juice in itself promotes the digestion of animal food, since acidic lysosomal hydrolases are activated in its cells. The secretion of hydrolases (proteases, phosphatases, esterases, etc.) by the secretory digestive glands, which have an optimum activity in an acidic environment, creates favorable conditions to digest food. The fundamental similarity of the process of acidic extracellular digestion in animals and plants was first pointed out by Darwin in his book “Insectivorous Plants” (1875).

The similarity of the physiology of digestion in animals and plants is no longer in doubt. It is currently known that acidification of the environment in the stomach of animals occurs as a result of the functioning of the H + pump in the plasmalemma of the cells of the gastric mucosa. Following the H + ions, chlorine anions enter the stomach cavity, compensating for the release of protons. For plants, chlorine is not an essential macronutrient and does not accumulate in large quantities in cells. Therefore, following the H + ions, it is not chlorine that leaves the secretory cells of the digestive organs of insectivorous plants, but anions of organic acids, primarily formic acid. The properties of the acid protease of insectivorous plants are also similar to gastric pepsin, the maximum activity of which is observed at pH 1-2.

Meaning insectivorous™. Many insectivorous plants live on soils poor in mineral elements. Their root system poorly developed. These plants, unlike other marsh plants, as a rule, do not have mycorrhiza, so the absorption of mineral elements from caught prey is of great importance for them. From the body of the prey, insectivorous plants obtain nitrogen, phosphorus, potassium, and sulfur. Carbon contained in amino acids and other breakdown products is also involved in the metabolism of insectivorous plants. Darwin also showed that if sundew plants are fed with pieces of meat, then after three months they are significantly superior to control plants in a number of indicators, especially reproductive ones. It has been established that bladderwort plants bloom only after receiving animal food.

The property of insectivorous plants to feed carnivorously is based on the ability of any plant cell to use for its nutrition organic substances released from a reserve form or flowing from other parts of the plant. In general, plant organisms are, as a rule, autotrophic, but carbon compounds synthesized during photosynthesis from CO 2 and water are then transferred from the leaves to all other parts of the plant, which feed on these ready-made organic substances, i.e. heterotrophically. In cases where the plant organism uses reserve organic substances (carbohydrates, proteins, fats) or cytoplasmic biopolymers (for example, from aging leaves), these substances must first be hydrolyzed and thus converted into a transportable and digestible form. This process is not fundamentally different from digestion in insectivorous plants.

Digestive processes in the endosperm. The most convenient object for studying the digestion process in plants is germinating seeds, which have an endosperm with reserves of organic nutrients deposited in it. In mature grains of cereals, the embryo does not directly contact the endosperm tissues. To mobilize and absorb reserve organic substances (polysaccharides, proteins), a modified cotyledon is used - the scutellum (Fig. 7.2). Essentially, the functional role of the scutum is similar to that of the stomach of animals. It can be expected that the mechanism of digestion of insoluble reserve polysaccharides and endosperm proteins during seed germination is fundamentally similar to what occurs during the digestion of animal tissues in insectivorous plants and with the digestive processes in the stomach of animals.

Indeed, the H + pump functions in the epithelial cells of the scutellum, and the scutellum secretes organic acids (citric, etc.) into the endosperm. As a result of acidification of the endosperm cells, which are half-dead (the nuclei and many organelles in the storage cells of the endosperm are destroyed during the ripening of the grains), acid hydrolases, primarily α-amylases, are activated in them, and starch is decomposed to maltose and glucose. Following the secretion of acids, the epithelial cells of the scutellum secrete acid hydrolases into the endosperm: α- and β-amylase, cellulase, proteases, various glucanases, phosphatase, RNase, etc.

Following the scutellum, on the third or fourth day of germination, the only living layer of cells in the endosperm, the peripheral aleurone layer, is also connected to the digestive activity of the scutellum (Fig. 7.2). Aleurone cells also secrete organic acids and acid hydrolases (α-amylase, proteases, RNase, etc.) into the endosperm. The combined activity of the scutellum and the aleurone layer leads to the dissolution of endosperm reserve substances.

The scutellum is also a suction organ. The plasmalemma of the epithelial cells of the scutellum, bordering the endosperm, carries out the transfer of sugars, amino acids, inorganic cations and anions from the endosperm into the cytoplasm of the cells of the scutellum, followed by the entry of transported nutritional compounds into the vascular bundles, which deliver these compounds to the growing embryo. This process is associated with the work of membrane H + pumps, which create proton motive force. The transfer of organic substances through the plasma membrane of the epithelial cells of the scutellum occurs in symport with H + ions.

It is important to note that the processes of mobilization of reserve substances in the endosperm are under hormonal control. The secretory activity of the scutellum is activated by cytokinin and auxin, and the synthesis and secretion of hydrolases in aleurone cells are completely under the control of gibberellin, which enters the aleurone cells from the scutum and the embryo.

The dissolution and outflow of storage substances from other storage organs, for example from the cotyledons of dicotyledons during seed germination, apparently occurs in a similar way. However, in this case, it is not extracellular, but intracellular acid digestion that occurs. These processes have not yet been sufficiently studied.

Mobilization of storage protein in germinating seeds. The seasonal periodicity of plant development includes dormant periods, before the onset of which assimilates flowing from the leaves are stored. These stored nutrients are needed to begin growth in the next growing season. Storage tissues of seeds, roots, stems, tubers are containers for nutrient reserves. Accumulation in cells large quantity nitrogen, carbon and other elements require the formation of osmotically inactive or weakly active components. These are the macromolecular forms of reserve nutrients: proteins, polysaccharides, triglycerides. The protein content in the seeds is quite high. The most protein is in the seeds of legumes (20 - 30%) and oilseeds (17 - 42%). In cereal seeds it is 7-14% by dry weight. Storage proteins are localized in aleurone grains and protein bodies and are represented by globulins (the main form in dicotyledons) and albumins. There are also prolamins and glutelins.

Aleurone grains are storage organelles of cells ranging in size from 0.1 to 25 microns. Surrounded by a single membrane. Protein content 70 - 80% by dry weight. The composition of aleurone grains also includes carbohydrates, phospholipids, phytin, RNA, and oxalic acid salts. There are complex and simple aleurone grains. Complex aleurone grains are characteristic of some dicotyledons and have inclusions of two types - globoid and crystalloid, surrounded by amorphous material. About 60% of the total protein content in aleurone grains is concentrated in the crystalloid, 35-40% in the amorphous zone, and 3-5% in the globoid. Some of the storage proteins in aleurone grains form complexes with phytin, carbohydrates and lipids, which are hydrolyzed first during germination. Phytin, a calcium-magnesium salt of inositol phosphoric acid, is localized in the globoid. The aleurone cells of the starchy endosperm of cereals contain simple aleurone grains. They are smaller in size than complex ones and do not contain inclusions. Phytin is localized in their amorphous protein matrix. Aleurone grains contain some acid hydrolases.

Protein bodies are found in the starchy endosperm of cereal grains. These heterogeneous systems, including, in addition to various groups of storage proteins, starch, lipids and a number of acid hydrolases, have dimensions of several micrometers.

The breakdown of proteins in seeds begins almost immediately after the onset of swelling and is carried out by several groups of proteases. There are three stages of proteolysis of storage proteins during germination. At the first stage, only limited proteolysis of the bulk of storage proteins occurs. Albumins and globulins localized in axial organs embryo, in aleurone grains of the aleurone layer. The mobility and solubility of proteins increases. Protein hydrolysis at this stage supplies the amino acids necessary for the synthesis of new enzymatic proteins. At the second stage, which lasts 5-10 days, proteins in storage organs quickly break down into amino acids, which are transported to the growing embryo, providing its heterotrophic nutrition. At the final stage, the structural and enzymatic proteins that ensure the digestion process are completely degraded in the storage organs.

Dicotyledonous seeds are characterized by intracellular digestion of proteins. Their breakdown occurs in the same cells in which they are stored. Significant changes in the structure of aleurone grains are noticeable within 3 - 5 days from the beginning of swelling. The activity of acid hydrolases - phosphatase and protease - increases sharply in them. The proteins of the amorphous matrix disappear first, then the protein crystalloids, and lastly the globoids. How the acidic pH level of aleurone grains is maintained is unknown. Perhaps the oxalic acid found in them is involved in acidification. For complete hydrolysis of proteins, aleurone grains lack their own proteases. Additional endopeptidase is synthesized in the endoplasmic reticulum, which is adjacent to the aleurone grains. As protein reserves are depleted, aleurone grains turn into vacuoles.

In cereal grains, along with intracellular digestion in the aleurone layer, scutellum and embryo, extracellular digestion of non-living cells of the starchy endosperm also occurs. Extracellular digestion occurs under the action of the scutellum and cells of the aleurone layer, which secrete acids into the endosperm, and then a number of acid hydrolases, including proteases (see Fig. 7.2). The release of acids into the endosperm leads to its acidification, which creates optimal conditions for the work of hydrolases that have an optimum action at pH 4 - 6, as well as for transport systems in the epithelial cells of the scutellum adjacent to the endosperm and transporting hydrolysis products from the endosperm into the conducting vessels of the scutellum. It has been established that amino acids and dipeptides are transported much more efficiently at acidic pH values ​​of the external environment. The secretion of hydrolases by corn corymbs is also most intense at pH 5.4 - 6.0.

Thus, acidification of the endosperm - important stage in the germination of grains, since it adjusts the entire system of acidic extracellular digestion and transport to the working rhythm. Low molecular weight peptides, formed together with amino acids during the hydrolysis of proteins, are absorbed by the scutes and are immediately hydrolyzed by alkaline endopeptidase to amino acids.

In the cotyledons of pumpkin and legumes, the breakdown of proteins begins in the aleurone grains near the epidermis and vascular bundles, then in the columnar parenchyma, and lastly in the cells of the spongy parenchyma. In the endosperm of cereals, protein bodies first disintegrate near the scutellum, then in the aleurone layer. Noticeable loss nitrogen in the starchy endosperm is observed already on the second day from the beginning of swelling. In the cells of the aleurone layer, protein hydrolysis begins later, on the 3rd -5th day.

Mobilization of stored carbohydrates. Carbohydrates are the most important group of reserve nutrients in seeds. Some seeds contain a small supply of sucrose, as well as other sugars (depending on the type): stachyose, maltose, galactose, ribose, fructose, glucose. Often these sugars are associated with proteins in glycoprotein complexes. However, the main storage polysaccharide in seeds is starch. Cereal seeds contain 50 - 76% starch by dry weight (corn and sorghum - up to 76, wheat and barley - up to 70%), legumes - 50-60% (peas - up to 50, beans - up to 60%). Starch is deposited in plastids during seed maturation. When starch grains grow to full size, the lamellar structure of the plastids is destroyed. The size of starch grains in the seeds of various plants varies from approximately 15 (rice) to 50 μm in diameter (beans). In addition to sugars and starch, polysaccharides that are part of cell walls can act as reserve carbohydrates. These are primarily hemicelluloses (galacto-mannans, glucofructans, etc.).

During germination, reserves of free sugars quickly disappear. Starch granules, which are in close contact with the cytoplasm, begin to disintegrate. Roughness is found on their surface, indicating that hydrolysis has begun. During the early stages of germination, some of the starch is broken down by phosphorylase. Gradually, the rate of phosphorolysis decreases and another, more powerful mechanism for the breakdown of starch using amylases is activated - hydrolytic. To completely break down starch into glucose hydrolytically, a whole complex of enzymes is required: the most important of them are α- and β-amylases, as well as α-glucosidase and limiting dextrinase.

Digestion of starch occurs both inside the cell and extracellularly. Intracellular digestion is characteristic of the seeds of dicotyledonous plants and begins already in the first hours of swelling in the axial organs. The starch content in pea cotyledons begins to decrease only from the 4th to 5th day of germination.

The course of starch breakdown has been best studied in cereal grains, where the bulk of it is involved in metabolism through extracellular digestion. The hydrolysis process begins from the scutellum and spreads to the distal part of the endosperm. In the endosperm zone adjacent to the scutellum, starch grains are destroyed already 20 hours after the beginning of caryopsis swelling. Epithelial cells of the scutellum secrete α- and β-amylases, first reserve forms, and then newly synthesized. The scutellum provides up to 17% of the total amylase activity of the endosperm. The release of s-amylase by the cells of the aleurone layer into the endosperm begins on the 3rd - 4th day. During this period, the endosperm starch is already partially digested, destruction of cell walls is observed, which facilitates the process of secretion and digestion.

Digestion of fats. Over 75% of the seeds of all flowering plant species contain fats as a nutritional reserve used during germination. Reserves of both neutral fats and significant amounts of polar lipids are concentrated in spherosomes. These are spherical particles with a diameter of up to 0.5 microns, and sometimes more, surrounded by a single membrane. Acid lipase activity was detected in spherosomes. The main functions of spherosomes are the storage and digestion of fats. In cereals, this process begins immediately after the beginning of swelling of the grains, although its speed is initially low and reaches a maximum on the 3-4th day from the beginning of swelling. In oilseeds, the breakdown of reserve fats begins on the 2nd -3rd day from the beginning of swelling and occurs, as in other groups of plants, in three stages. At the first stage, fats are broken down into glycerol and fatty acids by the enzyme lipase; in the second, fatty acids are broken down during oxidation to acetyl-CoA, which in the third stage can be converted into other compounds (see 4.24 and 4.42) or undergo further oxidation.

The key role in the digestion of fats belongs to acid lipase, which has low specificity and breaks down all glycerides. It can be deposited in ripening seeds, or can be synthesized again during seed germination in the endoplasmic reticulum, and then transported to the cell spherosomes. During seed germination, close contact of spherosomes with glyoxysomes is observed, in which, under the action of alkaline lipase, further decomposition of monoglycerides occurs, as well as β-oxidation of fatty acids. Reactions of the glyoxylate cycle also occur there, in which acetyl-CoA can be converted into succinic and oxaloacetic acids. Another product of fat breakdown, glycerol, is reduced to phosphodioxyacetone and can then be converted into sugars by gluconeogenesis (see Fig. 4.11).

The importance of studying heterotrophic nutrition is determined by the fact that all non-green plant organs (roots, flowers, fruits) and all plant cells in the dark feed heterotrophically.

Nutrition is a unique process in which the body receives the necessary energy and nutrients for cellular metabolism, repair and growth.

Heterotrophs: general characteristics

Heterotrophs are those organisms that use organic food sources. They cannot create organic substances from inorganic ones, as is done in the process of photo- or chemosynthesis by autotrophs (green plants and some prokaryotes). That is why the survival of the described organisms depends on the activity of autotrophs.

It should be noted that heterotrophs are humans, animals, fungi, as well as some plants and microorganisms that are incapable of photo- or chemosynthesis. It must be said that there is a certain type of bacteria that use light energy to form their own organic substances. These are photoheterotrophs.

Heterotrophs get food different ways. But they all boil down to three basic processes (digestion, absorption and assimilation), in which complex molecular complexes are broken down into simpler ones and absorbed by tissues, followed by use for the needs of the body.

Classification of heterotrophs

All of them are divided into 2 large groups - consumers and decomposers. The latter are the final link in the food chain, since they are capable of converting into. Consumers are those organisms that use ready-made organic compounds that were formed during the life of autotrophs without their final conversion into mineral residues.

If we talk about the types of heterotrophic nutrition, we should mention the holozoic species. Such nutrition is usually typical for animals and includes the following stages:

• Grabbing food and swallowing it.
• Digestion. It involves breaking down organic molecules into smaller particles that are more easily soluble in water. It should be noted that food is first mechanically crushed (for example, by teeth), after which it is exposed to special digestive enzymes (chemical digestion).
• Suction. Nutrients either immediately enter the tissues, or first into the blood, and then with its current into various organs.
• Assimilation (process of assimilation). It is about using nutrients.
• Excretion is the removal of end products of metabolism and undigested food.

Saprotrophic organisms

As already noted, organisms that feed on dead organic matter are called saprophytes. To digest food, they secrete appropriate enzymes and then absorb substances resulting from such extracellular digestion. Fungi are heterotrophs that are characterized by a saprophytic type of nutrition - these are, for example, yeasts or fungi Mucor, Rhizppus. They live on and secrete enzymes, and the thin and branched mycelium provides a significant absorption surface. In this case, glucose goes into the process of respiration and provides the mushrooms with energy, which is used for metabolic reactions. It must be said that many bacteria are also saprophytes.

It should be noted that many compounds that are formed during the feeding of saprophytes are not absorbed by them. These substances enter the environment, after which they can be used by plants. That is why the activity of saprophytes plays an important role in the circulation of substances.

Symbiosis concept

The term “symbiosis” was introduced by the scientist de Bary, who noted that there are associations or close relationships between organisms of different species.

Thus, there are heterotrophic bacteria that live in the digestive canal of herbivorous chewing animals. They are able to digest cellulose by feeding on it. These microorganisms can survive in the anaerobic conditions of the digestive system and break down cellulose into simpler compounds that host animals can independently digest and assimilate. Another example of such a symbiosis is plants and root nodules of bacteria of the genus Rhizobium.

To summarize, we can say that heterotrophs are an extremely wide group of living beings that not only interact with each other, but are also capable of influencing other organisms.