The substrate for the process of respiration is atf. Substrates of respiration. Anaerobic respiration of cereal seeds

Breath is the oxidation organic matter, which is the substrate of respiration. The substrates for respiration are carbohydrates, fats and proteins.

Carbohydrates. In the presence of carbohydrates, most cells use them as substrates. Polysaccharides (starch in plants and glycogen in animals and fungi) are involved in the respiration process only after they have been hydrolyzed to monosaccharides.

Lipids (fats or oils). Lipids constitute the "main reserve" and are put into action mainly when the supply of carbohydrates is exhausted. They must first be hydrolyzed to glycerol and fatty acids. Fatty acids are rich in energy and some cells, such as muscle cells, normally receive part of the energy they need from them.

Squirrels. Since proteins have a number of other important functions, they are used for energy production only after all the stores of carbohydrates and fats have been used up, for example during prolonged fasting (Section 8.9.3). Proteins are pre-hydrolyzed to amino acids, and amino acids are deaminated (lose their amino groups). The acid formed as a result of deamination is involved in the Krebs cycle or is first converted into a fatty acid in order to then be oxidized.

The main role in cellular respiration is played by two types of reactions - oxidation and decarboxylation.

Oxidation

Three types of oxidative reactions occur in the cell.
1. OXIDATION WITH MOLECULAR OXYGEN.

2. HYDROGEN REMOVAL (DEHYDROGENATION). During aerobic respiration, glucose oxidation occurs through successive dehydrogenation reactions. The hydrogen split off during each dehydrogenation is used to reduce the coenzyme, in this case called the hydrogen carrier:

Most of these reactions takes place in the mitochondria hydrogen carrier coenzyme NAD (nicotinamide adenine dinucleotide) usually serves:

OVER*H ( restored NAD) is then re-oxidized to release energy. Enzymes that catalyze dehydrogenation reactions are called dehydrogenases. In a series of successive dehydrogenation reactions, all hydrogen split off from glucose is transferred to hydrogen carriers. This hydrogen is then oxidized by oxygen to water, and the energy released in this process is used to synthesize ATP. The phenomenon of energy release during the oxidation (combustion) of hydrogen can be observed if you bring a burning candle to a test tube with hydrogen. At the same time, a light short pop will be heard, like a miniature explosion. The same amount of energy is released in the cell, but it is released in a series of redox reactions during the transition of hydrogen from one carrier to another along the so-called respiratory chain.

3. ELECTRON TRANSFER. This happens, for example, during the transition of one ionic form of iron (Fe2+) to another (Fe3+)

Electrons can be transferred from one compound to another, like hydrogen in the reactions described above. The compounds between which this transfer takes place are called electron carriers. This process takes place in the mitochondria.

Decarboxylation

Decarboxylation is the removal of carbon from a given compound to form CO2. In addition to hydrogen and oxygen, a glucose molecule contains six more carbon atoms. Since only hydrogen is needed for the above reactions, carbon is removed in decarboxylation reactions. The resulting carbon dioxide is a "by-product" of aerobic respiration.

Plants use carbohydrates as the main substrate for respiration, and free sugars are oxidized first. With their deficiency, polysaccharides, proteins, fats can be used after their hydrolysis. Poly- and disaccharides are hydrolyzed to monosaccharides, proteins to amino acids, fats to glycerol and fatty acids.

The use of fats begins with their hydrolytic cleavage by linden to glycerol and fatty acids, which occurs in spherosomes. Thanks to phosphorylation and subsequent oxidation, glycerol is converted into phosphotriose - PHA, which is included in the main pathway of carbohydrate metabolism.

Fatty acids are oxidized by the β-oxidation mechanism, as a result of which two-carbon acetyl residues are sequentially cleaved from the fatty acid in the form of acetyl-CoA. This process occurs in glyoxysomes, where, in addition, the enzymes of the glyoxylate cycle are localized. Acetyl-CoA is involved in the reactions of the glyoxylate cycle, the end product of which, succinate, leaves the glyoxisome and participates in the Krebs cycle in mitochondria (Fig.). Malate synthesized in the CTC in the cytoplasm with the participation of malate dehydrogenase is converted into oxaloacetate, which, with the help of PEP carboxylase, gives PEP. PHA and PEP serve as the starting material for the synthesis of glucose (as well as fructose and sucrose) in the reverse reactions of glycolysis. The process of formation of glucose from non-carbohydrate precursors is called gluconeogenesis. . It has been experimentally proven that as the seeds germinate, the content of fats decreases and the content of sugars increases.

Storage proteins are used for respiration by hydrolysis to amino acids and subsequent oxidation to acetyl-CoA or keto acids, which then enter the Krebs cycle (Fig.)

The complete oxidation of the considered substrates is carried out to carbon dioxide and water with the release of the energy of the oxidized substances.

The ratio of the number of moles of CO 2 released during respiration to the number of moles of absorbed O 2 is called the respiratory coefficient (RC). For hexoses equal to one:/

C 6 O 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O; DK \u003d 6CO 2 / 6O 2 \u003d 1

The amount of oxygen required for the oxidation of the substrate is inversely related to its content in the substrate molecule. Therefore, if the substrate for respiration is fatty acids that are poorer in oxygen (compared to carbohydrates), then the DC will be less than one:

C 18 H 36 O 2 + 26O 2 → 18CO 2 + 18H 2 O; DC \u003d 18 CO 2 / 26 O 2 \u003d 0.69

The value of DC is also affected by other factors, for example, lack of oxygen (when the roots are flooded, etc.), fermentation intensifies and DC increases; if, as a result of under-oxidation of products, organic acids accumulate in the tissues, and the amount of carbon dioxide decreases, DC decreases.

Rice. Use of polysaccharides, proteins and fats as respiratory substrates.

1. Dependence of respiration on environmental factors

1. Oxygen concentration

The process of respiration is associated with the continuous consumption of oxygen. But oxidative transformations of substrates include aerobic and anaerobic processes (glycolysis, fermentation). The decrease in the partial pressure of oxygen from 21% to 5%, the intensity of tissue respiration changes slightly.

For the first time, L. Pasteur discovered the effect of oxygen on the amount of consumption of respiratory substrates. In his experiments with yeast in the presence of oxygen, the breakdown of glucose and the intensity of fermentation decreased, but at the same time an intensive increase in biomass was observed. The inhibition of the decomposition of sugars and their more efficient use in the presence of oxygen is called the "Pasteur effect". This is due to the fact that at a high partial pressure of oxygen, the entire pool of ADP and P is spent on the synthesis of ATP. As a result, glycolysis is inhibited due to a decrease in the amount of ADP and P required for substrate phosphorylation, and a high ATP content inhibits some glycolytic enzymes (phosphofructokinase). As a result, the intensity of glycolysis decreases and synthetic crocesses (gluconeogenesis) are activated.

An important factor, which determines the intensity of cell respiration, is the concentration of ADP. The dependence of the rate of oxygen consumption on the concentration of ADP is called respiratory control, or acceptor control of breathing. The ratio of the sum of the concentrations of ATP and 1/2ADP to the sum of the concentrations of ATP, ADP, AMP is called energy charge.

An excess of oxygen in plant tissues can occur only locally. In an atmosphere of pure oxygen, plant respiration decreases, and then the plant dies. This is due to an increase in free radical reactions in cells, oxidation of membrane lipids, and, as a result, a violation of all metabolic processes.

2. Carbon dioxide concentration

Increasing the concentration of CO 2 leads to a decrease in the intensity of respiration, because. decarboxylation reactions and succinate dehydrogenase activity are inhibited. When there is acidification of tissues - acidosis.

3. Temperature

Respiration, as an enzymatic process, depends on temperature. Within certain temperature limits, this dependence obeys the van't Hoff rule (speed chemical reactions doubles when the temperature rises by 10°C). For the respiration of each plant species and its organs, there are certain minimum, optimal and maximum temperatures.

4. Water regime

In the leaves of seedlings, with a rapid loss of water, an increase in respiration is noted at the beginning. With a gradual decrease in water cut, this does not happen. Prolonged water deficiency leads to decreased respiration. The influence of water is especially clearly seen in the study of seed respiration. With an increase in seed moisture up to 14-15%, respiration increases 3-4 times, up to 30-35% - thousands of times. In this case, temperature plays an important role.

5. Mineral nutrition

Adding a salt solution to the water where the seedlings were grown usually enhances root respiration. This effect is called "salt breathing". In the tissues of other organs, this effect can not always be obtained.

1. Damage and mechanical impacts

Mechanical effects cause short-term increases in oxygen uptake for three reasons: 1) due to the rapid oxidation of phenolic and other compounds that leave the vacuoles of damaged cells and become available for the corresponding oxidases; 2) due to an increase in the amount of substrate for respiration; 3) due to the activation of recovery processes membrane potential and damaged cellular structures.

There are two main systems and two main pathways for the conversion of the respiratory substrate, or carbohydrate oxidation:

• glycolysis + Krebs cycle (glycolytic);
• pentose phosphate (apotomic).

The relative role of these respiratory pathways may vary depending on the type of plants, age, developmental phase, and also depending on environmental factors. The process of respiration of plants is carried out in all external conditions under which life is possible. The plant organism does not have adaptations for temperature regulation, therefore the respiration process is carried out at a temperature of -50 to +50°C. Plants have no adaptations to maintain an even distribution of oxygen throughout all tissues. Exactly the need to carry out the breathing process in a variety of conditions led to the development in the process of evolution of various pathways of respiratory metabolism and to an even greater variety of enzyme systems that carry out individual stages of respiration. It is important to note the relationship of all metabolic processes in the body. Changing the way of respiratory exchange leads to profound changes in the entire metabolism of plants.

Glycolytic pathway of respiratory metabolism is the most common and, in turn, consists of two phases. First phase - anaerobic (glycolysis), the second phase - aerobic. These phases are localized in different compartments of the cell. The anaerobic phase of glycolysis is in the cytoplasm, the aerobic phase is in the mitochondria.

Anaerobic phase of respiration (glycolysis) carried out in all living cells of organisms. In the process of glycolysis, a hexose molecule is converted to two molecules of pyruvic acid:

С6Н1206 -> 2С3Н402 + 2Н2.

This oxidative process can proceed under anaerobic conditions (in the absence of oxygen) and proceeds through a series of stages. First of all, in order to undergo respiratory breakdown, glucose must be activated. Glucose activation occurs by phosphorylation of the sixth carbon atom due to interaction with ATP:

glucose + ATP -> glucose-6-phosphate + ADP

At the next stage, ATP is formed due to the existing macroergic bond in 1,3-diphosphoglyceric acid. The process is catalyzed by the enzyme phosphoglycerate kinase:

Thus, at this stage, the energy of oxidation is accumulated in the form of the energy of the ATP phosphate bond. Then 3-FHA is converted to 2-FHA, in other words, the phosphate group is transferred from position 3 to position 2. Reaction 1 is catalyzed by the enzyme phosphoglyceromutase and proceeds in the presence of magnesium:

Further dehydration of FHA occurs. The reaction proceeds with the participation of the enolase enzyme in the presence of Mg2+ or Mn2+ ions. Dehydration is accompanied by a redistribution of energy within the molecule, resulting in a macroergic bond. Phosphoenolpyruvic acid (PEP) is formed:

The enzyme pyruvate kinase then transfers the energy-rich phosphate group to ADP to form ATP and pyruvic acid. For the reaction to proceed, the presence of Mg2+ or Mn2+ ions is necessary:

Since the breakdown of one glucose molecule produces two PHA molecules, all reactions are repeated twice. Thus, the total equation of glycolysis. As a result of the glycolysis process, four ATP molecules are formed, but two of them cover the cost of the initial activation of the substrate. Therefore, two ATP molecules accumulate. The formation of ATP in the process is as follows:

The glycolysis reaction is called substrate phosphorylation, since macroergic bonds arise on the molecule of the oxidized substrate. If we assume that during the breakdown of ATP, 30.6 kJ is released from ADP and Fn, then only 61.2 kJ accumulates in macroergic phosphate bonds during the period of glycolysis. Direct determinations show that the breakdown of a glucose molecule to pyruvic acid is accompanied by the release of 586.6 kJ. Consequently, the energy efficiency of glycolysis is low. In addition, 2 NADH molecules are formed, which enter the respiratory chain, which leads to additional education ATP. The resulting two molecules of pyruvic acid are involved in the aerobic phase of respiration.

Pentose phosphate pathway is a direct oxidation of glucose and occurs in the cytoplasm of cells. The highest activity of enzymes of the pentose phosphate pathway was found in the cells of the liver, adipose tissue, adrenal cortex, breast during lactation, mature erythrocytes. Low level of this process was found in skeletal and cardiac muscles, brain, thyroid gland, and lungs.

The pentose phosphate pathway is also called the apotomic pathway, since in its reactions the hexose carbon chain is shortened by one atom, which is included in the CO2 molecule.

The pentose phosphate pathway performs two important metabolic functions in the body:

• it is the main source of NADPH for the synthesis of fatty acids, cholesterol, steroid hormones, microsomal oxidation; in erythrocytes, NADPH is used to restore glutathione, a substance that prevents peroxide hemolysis;
• it is the main source of pentoses for the synthesis of nucleotides, nucleic acids, coenzymes (ATP, NAD, NADP, CoA-SH, etc.).

Two phases can be distinguished in the pentose phosphate pathway - oxidative and non-oxidative.

original substrate oxidative phase is glucose-6-phosphate, which is directly dehydrogenated with the participation of NADP-dependent dehydrogenase (reaction 1). The reaction product is hydrolyzed (reaction 2), and the resulting 6-phosphogluconate is dehydrogenated and decarboxylated (reaction 3). Thus, the carbon chain of the monosaccharide is shortened by one carbon atom (“apotomy”), and ribulose-5-phosphate is formed.

Reactions of the oxidative phase of the pentose phosphate pathway.

non-oxidizing phase The pentose phosphate pathway begins with isomerization reactions. During these reactions, one part of ribulose-5-phosphate isomerizes into ribose-5-phosphate, the other part into xylulose-5-phosphate

Isomerization reactions of ribulose-5-phosphate.

The following reaction proceeds with the participation of the transketolase enzyme, the coenzyme of which is thiamine diphosphate (a derivative of vitamin B1). In this reaction, a two-carbon fragment is transferred from xylulose-5-phosphate to ribose-5-phosphate:

The resulting products interact with each other in a reaction catalyzed by transaldolase and consists in the transfer of the dihydroxyacetone residue to glyceraldehyde-3-phosphate.

The product of this reaction, erythrose 4-phosphate, participates in the second transketolase reaction along with the following xylulose 5-phosphate molecule:

Thus, three molecules of pentose phosphates as a result of the reactions of the non-oxidative stage are converted into two molecules of fructose-6-phosphate and one molecule of glyceraldehyde-3-phosphate. Fructose-6-phosphate can isomerize to glucose-6-phosphate, and glyceraldehyde-3-phosphate can undergo oxidation in glycolysis or isomerize to dihydroxyacetone phosphate. The latter, together with another molecule of glyceraldehyde-3-phosphate, can form fructose-1,6-diphosphate, which is also capable of converting to glucose-6-phosphate.

Through the pentose phosphate pathway, complete oxidation of glucose-6-phosphate to six CO2 molecules. All these molecules are formed from the C-1 atoms of six molecules of glucose-6-phosphate, and from the six molecules of ribulose-5-phosphate formed, five molecules of glucose-6-phosphate are again regenerated:

If we simplify the presented scheme, we get:

Thus, the complete oxidation of 1 glucose molecule in the pentose phosphate pathway is accompanied by the reduction of 12 NADP molecules.

The question of the substances used in the process of respiration has long occupied physiologists. Even in the works of I.P. Borodin (1876) showed that the intensity of the respiration process is directly proportional to the content of carbohydrates in plant tissues. This gave reason to assume that it is carbohydrates that are the main substance consumed during respiration (substrate). In finding out this issue great importance has a definition of the respiratory coefficient. Respiratory coefficient(DC) is the volume or molar ratio of CO 2 released during respiration to that absorbed over the same period of time About 2 . With normal access to oxygen, the DC value depends on the substrate of respiration. If carbohydrates are used in the breathing process, then the process proceeds according to the equation C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O. In this case, DC is equal to one: 6CO 2 / 6O 2 \u003d 1. However, if decomposition during breathing more oxidized compounds, such as organic acids, are exposed, oxygen uptake decreases, DC becomes greater than one. So, if malic acid is used as a breathing substrate, then DC = 1.33. When more reduced compounds, such as fats or proteins, are oxidized during respiration, more oxygen is required and DC becomes less than unity. So, when using fats DC = 0.7. The determination of the respiratory coefficients of different plant tissues shows that under normal conditions it is close to unity. This gives reason to believe that the plant primarily uses carbohydrates as a respiratory material. With a lack of carbohydrates, other substrates can be used. This is especially evident in seedlings that develop from seeds, which contain fats or proteins as a reserve nutrient. In this case, the respiratory coefficient becomes less than one. When used as a respiratory material, fats are broken down into glycerol and fatty acids. Fatty acids can be converted to carbohydrates through the glyoxylate cycle. The use of proteins as a substrate for respiration is preceded by their breakdown into amino acids.

Exist two main systems and two main ways transformation of the respiratory substrate, or oxidation of carbohydrates: 1) glycolysis + Krebs cycle (glycolytic); 2) pentose phosphate (Apotomtesque). The relative role of these respiratory pathways may vary depending on the type of plants, age, developmental phase, and also depending on environmental factors. The process of respiration of plants is carried out in all external conditions under which life is possible. The plant organism does not have adaptations for temperature regulation, therefore

The breathing process is carried out at a temperature of -50 to +50°C. Plants have no adaptations to maintain an even distribution of oxygen throughout all tissues. It was the need to carry out the process of respiration under various conditions that led to the development in the process of evolution of various pathways of respiratory exchange and to an even greater variety of enzyme systems that carry out individual stages of respiration. It is important to note the relationship of all metabolic processes in the body. Changing the way of respiratory exchange leads to profound changes in the entire metabolism of plants.

2. From the scientists proposed below, the position (theory) about genetic

3. The most traditional substrates for respiration in plants are ...

8. In the process of breaking down one molecule of glucose to carbon dioxide

9. Oxygen splitting compared to anoxic in terms of energy ...

10. When carbohydrates are broken down, the greatest amount of ATP is synthesized ...

11. When one glucose molecule is broken down to pyruvic acid, it is additionally formed in the cell ...

12. Phosphorylation is the process of electron transfer along the respiratory chain, which goes with the formation ...

13. The greatest amount of energy is released during oxidation ...

2) microorganisms that decompose 4) plants that prefer the pyroorganic substances of the soil with the absorption of ammonium nitrogen. release of ammonia;

4. The conditional boundary between macroelements and microelements is determined

5. The reduction of nitrites to ammonium in the cell is carried out by the enzyme ...

10. In symbiotic nitrogen fixation, the source of energy for the breakdown of nitrogen molecules is ...

11. The reduction of nitrates to ammonium in plants is carried out ...

15. A sign of potassium deficiency is ...

17. The composition of the catalytic centers of many redox enzymes (cytochromes, catalase, peroxidase) includes ...

18. The composition of the catalytic centers of polyphenol oxidase and ascorbate

19. Cobalt is part of vitamin B12, which is necessary for the process of molecular nitrogen fixation. The most sensitive to the lack of cobalt is ...

Growth and development

8. What is the name of the irreversible growth movements of plants caused by a unilaterally acting factor?

9. What event in the growth zone of a root or stem, according to the Kholodny-Vent theory, is primary?

10. What are the names of plant rhythms with a period of about a day, which are endogenous in nature?

11. What are the reasons for the sharp decrease in growth rates in plants with a lack of water?

12. Which of the following signs are characteristic of etiolated

13. What type of tropisms does the movement of a wheat straw rising after lodging refer to?

14. What environmental factors are the main ones during the transition

2. What is the reason for the death of heat-loving plants at low positive temperatures?

3. What are the causes of plant death at low negative temperatures?

9. Why the use of fertilizers contributes to a more successful transition

10. What are the characteristics of plants grown from seeds treated for an hour with a 3% sodium chloride solution?

9. BRIEF INFORMATION ON THE FORMATION OF PLANT PHYSIOLOGY AND ON SCIENTIFIC PHYSIOLOGISTS

Plant physiology originally developed as component botany. The beginning of experimental plant physiology was laid by the experiments of the Dutch naturalist Jan Van Helmont. In 1629 he conducted the first physiological experiment, studying the nutrition of plants. He placed soil weighing 91 kg in an earthen vessel and planted a willow branch in it, the weight of which was 2.25 kg, and regularly watered it with rainwater. After 5 years, I separately weighed the soil and the branch. It turned out that the willow weighed 77 kg, and the weight of the soil decreased by only 56.6 g. Based on this experience, Helmont concluded that the mass of the plant consists of water. This is how water theory nutrition.

The stages of further development of plant physiology were associated with the discovery of photosynthesis. In 1771, Joseph Priestley discovered that mint plants placed in a vessel corrected the air in it, spoiled by the burning of a candle.

The Swiss botanist Jean Senebier in 1800 published the treatise "Physiology of Plants", in which he first defined the subject and tasks of plant physiology as an independent science and gave the name to this science.

Also, the main stages in the development of plant physiology are associated with the study of growth movements - tropisms (C. Darwin), the development of the theory of mineral nutrition (Yu. Liebig, J. B. Bussengo).

IN late XIX - early XX centuries. intensive study of the mechanisms of plant respiration began (V.I. Palladin, A.N. Bakh).

The founders of Russian plant physiology are Andrey Sergeevich Famintsyn and Kliment Arkadyevich Timiryazev. Research by A.S. Famintsyn are devoted to the metabolism and energy of plants. He is the author of the first domestic textbook on plant physiology (1887). The main studies of K.A. Timiryazev on plant physiology are devoted to the process of photosynthesis.

IN In 1934, the Institute of Plant Physiology was established in the system of the USSR Academy of Sciences, which in 1936 was named after K.A. Timiryazev. This institution played an important role in the development of Russian plant physiology. The names of such famous scientists as Anatoly Alexandrovich Nichiporovich are associated with him - the main works on the physiology of photosynthesis, the theory of photosynthetic productivity of plants

And its application in agriculture; Mikhail Khristoforovich Chailakhyan - the author of the hormonal theory of plant development (1937); Raisa