Conduction of organic matter in the plant. The movement of organic matter in a plant. What are the structural features of the cells of these tissues

How does the movement of substances occur in the plant, namely water with mineral salts dissolved in it?

Through the process of absorption, water and the salts dissolved in it enter from the soil into root system. Further movement of solutions of mineral salts carried along the stem from the root to the leaves of the plant. It is necessary to figure out which sections of the plant stem are actively involved in the transportation of water and salts: the core, wood or bark. You can conduct a simple experiment and put a branch of an apple tree or some other tree in water, where ink has previously been added. If a day later you pull the branch out of the water and cut the stem lengthwise, you will notice that only the layer of wood has changed color. The bark and core remained unchanged. Thus, we can conclude that it is through the wood that water moves with salt solutions from the root to the leaves.

The composition of the wood includes long cavities in the form of tubes, called the vessels of the plant. They are designed to move along the stem of water and mineral salts.
Principle movement along the stem of organic compounds somewhat different from that described above. It is known that due to the reserves of organic substances, the growth and nutrition of germinating seeds is carried out. You can observe how the branches of any tree placed in a vessel with water “let out” shoots with leaves, and they also quickly form adventitious roots under water. Obviously, the appearance of new structures is due to the presence of organic matter in the branches.
The movement of organic substances occurs along the bark of the stem. This is easy to prove if you remove the bark from a freshly cut branch of an acacia or chestnut in a small area closer to the lower edge, and then put the branch in water. After some time, a thickening or influx will appear above the cut bark, where young adventitious roots are visible. Below the place where the bark is removed, the roots either do not appear at all or are very thin and small. The conclusion suggests itself: a cut of the bark prevents organic matter from moving from the leaves to the roots of the plant. In this regard, an influx with adventitious roots is formed above the cut. Thus, this serves as irrefutable proof of the above statement that the transport of organic nutrients occurs along the bark of the plant stem.
These substances are distributed in such a way that, first of all, the growth of young parts of the plant is ensured. Moreover, they move both down to the root system and up to the shoots, flowers and fruits of the plant.

In every living organism, the movement of various substances (nutrient, oxygen, decay products, etc.) necessarily occurs. Plants have a transport conducting system. It connects the various parts of the plant and ensures the transfer of substances from one part to another. In lower plants - algae - there are no tissues and substances move from one cell to another. In higher plants, water, minerals and organic substances move along conductive tissues(Fig. 55).

Rice. 55. The scheme of movement of mineral and organic substances through the plant

It is known that the roots supply the plant with water and minerals. And the leaves, in turn, provide the roots with organic substances that are formed during photosynthesis. How does the movement of substances take place?

Water and minerals move through vessels that begin at the root, stretch through the stem into the leaf and reach each of its cells. Vessels - long tubes, which are dead cells, the transverse partitions between which have dissolved.

Organic substances are formed in the leaves and move to other organs - roots, flowers, fruits through sieve tubes. sieve tubes- living elongated cells, the transverse partitions of which are penetrated by the smallest pores. Sieve tubes are located in the cortex - on the inside.

Not all organic substances formed during photosynthesis are used for plant life. Part of the organic matter is deposited in the reserve. In wheat, oats and rye, organic substances are deposited in seeds, in carrots, beets and radishes - in root crops, in lily of the valley and wheatgrass - in rhizomes. In the seeds, organic substances serve to nourish the developing embryo, and those accumulated in the branches, rhizomes, and bulbs are used to form new organs.

Answer the questions

What is the importance of the movement of substances in the life of a plant organism?
Compare the paths of movement of mineral and organic substances through the plant.
What is the importance of deposition of organic matter in the stock?

New concepts

conductive tissues. Vessels. Sieve tubes.

Think!

How can you save a tree whose bark is damaged?

My laboratory

Experience 1. They cut off a linden shoot and placed it in water tinted with ink (Fig. 56, a). Four days later, a transverse section of the stem was made. On the cut, the colored fibers were clearly visible - the wood in which the vessels are located. Make a conclusion about the movement of water with minerals dissolved in it throughout the plant.

Rice. 56. The movement of substances along the shoot of a plant

If you place a sprig of a houseplant of balsam in tinted water, you can see how the water rises along the stem into the leaves, coloring their veins (Fig. 56, b).

Experience 2. Cut a ring from the top bark of a tree branch. Put the branch in the water. After a while, an influx forms over the cutout. This is an accumulation of organic matter that cannot move down through the cut ring of bark. Adventitious roots develop from the influx (Fig. 57).

Rice. 57. Formation of an influx on a branch after an annular cutting of the bark

What does this experience indicate? Make a conclusion.

The trunks are covered with bark on the outside, which protects them from evaporation, overheating, freezing, sunburn, and the penetration of harmful microorganisms. On the trunks of old birch, aspen, and alder trees, dead bark tissues are not able to stretch and often form cracks.

Through these cracks, spores of bacteria and fungi penetrate into the trunk, causing damage and death of the tree. The tinder fungus causes great harm to forestry (Fig. 58). Feeding on the juices of the tree, it destroys the wood, making it brittle and brittle. This leads to the death of the tree.

Rice. 58. Tinder fungus on a tree

Among the tinder fungus, a fungus is widespread - a real tinder fungus. It develops on dead wood of birch, aspen, and alder. Its fruiting bodies are attached to tree trunks with a wide base and are hoof-shaped. They live 12-15 years, reaching up to 1 m in diameter and weighing up to 10 kg. On the underside of the fruiting bodies, in tubules, spores ripen. They penetrate the tree through various damages: cracks, broken branches, etc. These fungi can spoil the harvested wood and even wooden buildings.

Some tinder fungi, such as birch fungus, form growths (chaga) on the trunks of living birches. Chaga has been used in folk medicine since the time of Vladimir Monomakh. It has anti-inflammatory, tonic and analgesic effects. Therefore, it is harvested as a medicinal raw material (befungin is obtained from it). In Siberia, chaga is used as a tea substitute.

Among the tinder fungi there are also edible mushrooms. They form soft bright orange annual fruiting bodies on the trunks of deciduous trees. These mushrooms are located one above the other in large groups and are edible only at a young age. The fruit bodies of many tinder fungi are used for various crafts: coasters, vases. Dried tinder fungi were once used together with flint and flint to kindle a fire.

The plant organism, unlike the animal, is characterized by great economy in the use of nutrients. This is expressed in the ability of plants to reutilize (reuse) the main elements of mineral nutrition. Each "leaf of a plant goes through its development cycle. The leaf grows, reaches its maximum size, then the aging process begins, and finally the leaf dies. Throughout the life of the leaf, nutrients enter it. At the same time, some amount of substance flows out of it. During the period of physiological youth of the leaf, the amount of substances containing elements of mineral nutrition in it increases, since the rate of influx of the substance. significantly exceeds the outflow rate. Then, for a short period, these two processes (inflow and outflow) balance each other. Finally, as the leaf ages, outflow begins to predominate. During flowering and leaf fall, the outflow of nutrients is intense from all leaves. Thus, nutritious. substances move from the root system to the above-ground organs, mainly along the xylem, and then flow from the leaves along the phloem to the tissues of the stem. Spreading in the radial direction from the conducting elements of the phloem, the nutrients pass back into the vessels of the xylem and are directed with an upward current to younger organs and leaves. Consequently, the nutrients cycle through the plant. The transition from the descending current (along the phloem) to the ascending current (along the xylem) can occur at different points of the stem. For nitrogen compounds, it was shown that the movement in the downward direction goes along the phloem to the root system. In the conducting system of the root, nitrogen compounds pass into an upward current and move through the vessels of the xylem. The repeated use of individual elements by the plant organism affects their distribution. AT There are two pronounced gradients in the distribution of mineral substances in the plant. Items that are reused are characterized by basipetal gradient distribution, i.e. the higher the leaf is, the younger it is; the more nitrogen, phosphorus, potassium. This is especially evident with a lack of this element in the soil. For elements that have not been reused (potassium, boron, iron), acropetal gradient distribution. The older the organ, the greater the content of these elements in it. With respect to recycled elements, signs of starvation will appear primarily on older leaves, while with respect to elements that have not been recycled, signs of suffering will appear first of all on young organs.

Features of the movement of organic substances through the plant

Leaves, or rather, chloroplasts, supply all organs of the plant organism with the organic substances formed in them. The ways of movement of these substances are heterogeneous. The substances formed in the chloroplast must first of all enter the cytoplasm, then along the parenchymal cells into the sieve tubes of the phloem and through them to the various consuming plant organs. There are intracellular, intercellular parenchymal and phloem transport of substances.

1. intracellular transport. Release of assimilates from chloroplastscomrade In each chloroplast, the amount of products formed during photosynthesis per day exceeds their own mass. In this regard, the outflow of assimilates to other parts of the cell, i.e., intracellular transport, is of great importance. Triose phosphates (PHA, FDA) penetrate most easily through the membranes of chloroplasts, which can leave the chloroplasts and re-enter them. The penetration of phosphorylated hexoses through the chloroplast membrane is difficult. It is assumed that more complex carbohydrates formed in chloroplasts break down into triose phosphates and in this form move to the cytoplasm, where they can serve as material for the resynthesis of hexoses, sucrose and starch. Due to these transformations, the concentration of triose phosphates in the cytoplasm continuously decreases, which contributes to their influx along the concentration gradient. Proteins formed in chloroplasts also break down and flow into the cytoplasm in the form of amino acids. In the light, the permeability of chloroplast membranes increases, which contributes to the outflow of various substances from them.

2. Intercellular parenchymal transport. The organic compounds that have entered the pithoplasm are not only used for the needs of this cell, but also move in a direction to the sieve tubes. Intercellular parenchymal transport can be carried out in two ways - through plasmodesmata (symplast) or through free space (cell membranes and intercellular spaces of the leaf parenchyma). Depending on the density of the conductive elements in the leaf (network of veins), the distances from the parenchymal cell producing assimilates to the sieve elements of the phloem can be different. However, on average, it does not exceed 3-4 cells and is hundredths of a millimeter. The speed of movement of assimilates in parenchymal tissues is approximately 10-60 cm/h. This is noticeably higher than the diffusion rate. When substances move along plasmodesmata, such a speed can be achieved only with a large additional expenditure of energy. However, not all plants have well developed plasmodesmata. All this suggests that parenchymal transport is carried out not only through plasmodesmata. In the leaf mesophyll, the free space (open for free diffusion) can include spaces between cellulose fibrils in cell walls, as well as the nixv system. It has been shown that the cells of the leaf mesophyll have this secretory ability and easily release sugars into the free space. Cells of phloem endings (transmitters) intensively absorb sugars and amino acids. A distinctive feature of transfer cells are numerous outgrowths of cell walls. Thanks to these outgrowths (directed inside the cells), the surface of the plasmalemma increases, at the same time it increases the capacity of free space - and creates favorable conditions for the release of substances into the phloem.

3. The movement of substances along the phloem is phloem transport. Long-distance transport of organic nutrients in a downward direction is carried out mainly through the phloem. Unlike xylem its composition includes sieve tubes proper, accompanying cells, cells of the phloem parenchyma and bast fibers. Sieve tubes are vertical rows of elongated, in most cases, cylindrical cells with thin cell membranes. Individual cells (segments) are separated from each other by sieve plates pierced by numerous pores through which cytoplasmic strands pass. Each cell of the sieve tube is adjacent to a satellite cell rich in cytoplasm. Unlike xylem phloem is a collection of living cells its composition includes sieve tubes proper, accompanying cells, cells of the phloem parenchyma and bast fibers. Sieve tubes are vertical rows elongated in most cases into cylindrical cells with thin cell membranes. Individual cells (segments) are separated from each other by sieve plates pierced by numerous pores through which cytoplasmic strands pass. Sieve tubes are formed from cambial cells and at first do not differ from other phloem cells. They contain mobile cytoplasm with numerous ribosomes, plastids, mitochondria. In the center there is a vacuole surrounded by a membrane - tonoplast. As development progresses, the structure of the tubes undergoes significant changes. The nucleus breaks up; plastids, mitochondria decrease in size; tonoplast disappears. In place of the vacuole, a central cavity is formed. The cytoplasm is located in the parietal layer. Separate longitudinal strands of cytoplasm penetrate the central cavity. The cavity contains clots of rounded shape, apparently, these are accumulations of microtubules. Simultaneously with these changes, pores are formed in the sieve plates through which thin strands of cytoplasm (filaments) pass; in some cases they take the form of microtubules. Apparently it is in during this period, sieve tubes serve as a place for the transport of substances. With aging, callose carbohydrate is deposited in the pores of the sieve plates. Callose, narrowing the gaps of the pores, makes it difficult for the movement of substances. In woody plants, individual elements of the phloem function for only one year. As new leaves form, the outflow from them goes along the newly organized sieve elements. Of great importance was the development of a method for obtaining phloem juice using sucking insects that immerse the proboscis in a sieve tube. If the body of an insect is cut off, phloem juice will flow out of the proboscis, which is analyzed. The use of 14 CO 2 made it possible to carry out the analysis of labeled compounds in the conducting elements of the phloem. Studies have shown that 90% or more of all substances moving through the phloem are carbohydrates. The main transport form of carbohydrates is sucrose (C 12 H 22 O 11). However, at of some species, along with sucrose, oligosaccharides (raffinose, stachyose) serve as a transport company for carbohydrates, and also some alcohols (mannitol, sorbitol), monosugars (glucose and fructose) make up a small proportion of the moving carbohydrates. It appears that the bulk of sucrose occurs in parenchymal cells of the phloem, from where it enters the reticulate tubes, which are devoid of enzymes that decompose sucrose (invertatases), which determines the safety of these compounds throughout the entire path of its transport. In the phloem in a downward direction: there may be movement of other nutrients, such as in the form of mineral and organic compounds during their outflow from aging organs in the process of recycling. Nitrogenous substances, when reused, move along the phloem in the form of amino acids and amides. Transport along the phloem can go in two opposite directions, the assimilates formed in the leaves move both up - to growth points, flowers and fruits, and down - to the roots, receptacles of spare nutrients. The determination of the speed of movement of substances along the phloem was carried out by observing the speed of distribution of labeled compounds. It turned out that the speed of movement in sieve tubes is quite high and averages 50-100 cm/h. In different groups of plants, the speed of movement varies somewhat. In the same plant, different organic substances can move at different speeds. Significant effect on movement speed environmental conditions. In contrast to movement through the xylem, the transport of substances through the phloem is influenced by all factors that change the intensity of metabolic processes. locomotion in the phloem depends from temperature. It turned out that the optimal temperature fluctuates between 20 and 30°C. A further increase in temperature already inhibits the outflow of assimilates from the leaf blade. The attitude to a sharp cooling of the phloem in different plants is not the same. So, southern plants (beans) completely stop transport at a temperature of 1-2 ° C, while in sugar beet such cooling only slows down movement. Conditions for mineral nutrition have a significant effect on the transport of substances through the phloem. Especially this research is devoted to the influence of boron. It has been shown that under the influence of boron, the rate of movement of sucrose noticeably increases. Perhaps this is due to the formation of complex compounds of boron with carbohydrates. Assimilate movement speed is accelerated, also under the influence of phosphorus. Phosphorylated forms of sugars move faster. Movement speed changes under the influence of potassium. Maybe potassium maintains the membrane potential in the sieve plates and thereby promotes the movement of substances through the phloem. The most difficult question is phloem transport mechanism. The driving force behind this flow is turgor pressure. Cells in which sugars are formed (donor) are characterized by high turgor pressure, and in which sugars are consumed - low turgor pressure (acceptor). if these cells are interconnected, it must flow from cells with high pressure to cells with low pressure. Movement does not always follow the turgor pressure gradient (in the direction of its decrease). Thus, it is impossible to explain the intense transfer of assimilates from falling leaves or wilting flower petals, which naturally possess; low turgor pressure. Calculations suggest that in order to move the sucrose solution at the speed observed in the sieve tubes, a force is needed that significantly exceeds the turgor pressure force developed in donor cells. An alternative hypothesis is the hypothesis according to which the movement of organic substances goes along the strands of the cytoplasm with the expenditure of energy. There is a relationship between phloem transport and the intensity of energy metabolism. The energy source for the transport of substances can be ATP, formed both in the sieve cells themselves and mainly in satellite cells. It has been shown that companion cells are characterized by exceptionally high intensity of respiration and phosphorylation.

Periodic contractions of the protein strands of the sieve tubes can promote the movement of substances in a certain direction. Electron microscopic studies have shown the presence of protein filaments and in pores of sieve plates. It is possible that these protein strands are capable of peristaltic contractions, which causes them to push through the solution or special carrier granules on which assimilates are concentrated. Of course, these peristaltic contractions require an expenditure of energy. Thus, the transport of assimilates through the phloem is carried out using several mechanisms. The main importance is attached to those mechanisms that are associated with the peristaltic contraction of protein strands. Important for the growth of plant organisms is directed assimilation movement. It is largely determined by the intensity of the use of substances, the needs of a particular organ, the intensity of its growth. Phytohormones are of great importance in the distribution of nutrients in a plant. The transport of nutrients is directed towards those organs that are characterized by a high content of phytohormones, in particular auxins. The treatment of individual plants with auxin causes an increase in the influx of various organic substances to them. The influence of phytohormones on the movement of assimilates is associated with an increase in the intensity of energy metabolism. The direction of movement of assimilates is somewhat limited by the location of the organs that produce them, namely the leaves. It is significant that the leaves located on different sides of the stem, as well as different in tier (upper and lower) supply the products of photosynthesis to various parts of the plant organs.

Chapter 7

A living cell is an open energy system, it exchanges energy with the external environment and lives due to the influx of energy from outside. A cell, an organism can retain its individuality only with the influx of free energy from the environment. As soon as this influx ceases, disorganization and death of the organism sets in.

The energy of sunlight, stored during photosynthesis in organic matter, is again released and used for a variety of life processes. The energy of light quanta, accumulated in carbohydrates, is quickly released again in the process of their decay (dissimilation). In the most general form, it can be noted that all living cells receive energy through enzymatic reactions, during which the electrodes move from a higher energy level to a lower one.

In nature, there are two main processes during which the energy of sunlight stored in organic matter, is released - this breath and fermentation. Respiration is the oxidative breakdown of organic compounds into simple ones accompanied by the release of energy. Fermentation is the process of seedling organic compounds into simpler ones, accompanied by the release of energy. During fermentation, the degree of oxidation of the compounds does not change. In the case of respiration, oxygen serves as an electron acceptor, in the case of fermentation, organic compounds. The processes included in the energy cycle are so important that at present the science of bioenergetics has arisen, which studies the molecular and submolecular foundations of energy transformation.

MOVEMENT OF SUBSTANCES
BY PLANT
1. Introduction. System organization
transport in plants.
2. Movement of mineral elements
plant nutrition.
3. Transport of organic substances.

I. The role of the study of the transport of substances:
theoretical value as one of
problems of physiology
practical value
interconnection of individual organs in
unified physiological system
Donor-acceptor connections between organs:
nutrient-supplying organs
donors
consuming organs are acceptors.
Name the donors
mineral nutritional
substances and organic
substances.

Marcello Malpighi
1628-1694
Malpighi experience with withdrawal
ring-shaped piece of bark
stem (A). swelling of tissue over
ring (B)
A big role in finding out the ways of movement
individual nutrients played reception
plant ringing.
This technique was applied at the end of the 17th century. (1679)
Italian researcher M. Malpighi,
who suggested that the
their soils go to the roots, then along
wood into leaves and stems (raw sap), and after
processing - in the opposite direction along the bark.

Organization of the transport system

Intracellular
Middle: within one organ, according to
nonspecific tissues, for short
distances.
Far: between different organs, according to
specialized fabrics. Transport by
xylem and phloem.

II. The movement of mineral nutrients throughout the plant

Name the mineral acceptors
How is intracellular transport carried out?
Name the transit systems
On what tissue is the far
mineral transport

Cycle of minerals in the plant. Recycling

The plant organism is characterized
economy in the use of nutrients
substances, which is expressed in the ability to
recycling (reuse)
the main elements of mineral nutrition.
Reusable
most elements of mineral nutrition, in
including P, N, K, Mg, etc.
Elements that are practically
reutilized - Ca and B, which is associated with a small
mobility and poor solubility
compounds that contain these
elements.
recycling

There are two distribution gradients of mineral substances in the plant:
elements that are reused are characterized by
basipetal distribution gradient, i.e. the higher the leaf is located and
the younger it is, the more nitrogen, phosphorus, potassium it contains.
for non-recyclable elements (calcium,
boron), an acropetal distribution gradient is characteristic. The older
organ, the greater the content of these elements in it.
The practical significance of the study of the distribution of nutrients in
plant organs:
- in relation to elements that are subject to reuse,
signs of starvation will appear, first of all, on older
leaves,
- in relation to elements that are not subject to recycling, signs
deficiencies appear primarily on young leaves.
Therefore, the gradient of plant suffering is directed in the opposite direction.
side of the distribution gradient.

III. TRANSPORT OF ORGANIC SUBSTANCES

1.
2.
3.
4.
Distribution of assimilates in the plant.
Ways of movement of assimilates.
transport mechanism.
Transport regulation.

1. Distribution of assimilates in the plant

Movement of assimilates
obeys the donor-acceptor pattern
photosynthetic tissues
Places of consumption
(growth centers:
meristems,
leaves, etc.)
storage places
(fruits, seeds,
storage
parenchyma, etc.)
Donors (sources)
assimilates photosynthetic
storage tissues
(organs).
Acceptors (consumers)
organs (tissues)
capable
on one's own
satisfy their
nutritional needs.
Uneven
distribution
assimilates

Movement along the phloem has no definite
direction, unlike xylem, depends
on the location of the donor and acceptor.

2. Ways of movement of assimilates

2.1. intracellular transport

This is the transport of assimilates from chloroplasts to the cytoplasm.
Starch → glucose → fructose diphosphate → trioses.
Trioses are released from chloroplasts with the help of transport proteins with
energy expenditure.
In the cytoplasm, trioses are used for respiration, the synthesis of hexoses,
sucrose, starch. This allows you to reduce the concentration
triose phosphates in the cytoplasm, which contributes to their influx along
concentration gradient.
The resulting sucrose does not accumulate in the cytoplasm, but
exported or temporarily accumulated in vacuoles,
forming a reserve pool

2.2. Intercellular parenchymal transport

Near transport can be carried out in two ways - along plasmodesmata
(symplast) or apoplast.
The speed of movement of assimilates in parenchymal tissues is 10-60 cm/h

From apoplast and symplast assimilates
enter the accompanying
(transmitting) cells (mediators
between leaf parenchyma cells
and sieve tubes)
They have numerous outgrowths
cell walls. Thanks to outgrowths
plasma membrane surface increases.
At the same time it increases
free space capacity and
creates favorable conditions for
substance absorption

Evidence for phloem transport

2.3. Phloem transport
Evidence for phloem transport
1) Ringing, 1679
ital. Marcello
Malpighi.
2) Usage
radioactive
14CO2 labels.
3) Receiving method
phloem juice with
suckers
insects.
This technique has received
name aphidnaya (from lat.
aphids - Aphidoidea)
Honeydew stands out - pad

Phloem structure

Unlike xylem, phloem is
is a collection of living cells.
The phloem is made up of several types of cells,
specialized in metabolic and
structurally:
sieve tubes (sieve cells) transport function
satellite cells - energetic role
transfer cells.

With the development of the ST structure
is undergoing changes:
the nucleus breaks up;
reduced in size and
the number of plastids and
mitochondria;
tonoplast disappears, in place
vacuoles form a cavity
EPR is smooth, in the form of stacks.
the cytoplasm is located in
wall layer.
plasmalemma is preserved in mature
cells
In the pores of the sieve plates is deposited
callose carbohydrate and phloem protein (P-protein)

companion cells

Attached to every cell
sieve tube.
Rich in cytoplasm
Large nucleus and nucleolus
Numerous mitochondria and
ribosomes
Have a high
metabolic activity,
supply sieve tubes
ATP.
Companion and sieve cells
tubes are connected
plasmodesmata.

Composition of phloem exudate

Composition of White Lupine Xylem & Phloem Sap
Xylem Sap (mg
l-1)
Phloem Sap (mg
l-1)
Sucrose
*
154,000
amino acids
700
13,000
Potassium
90
1,540
Sodium
60
120
Magnesium
27
85
Calcium
17
21
iron
1.8
9.8
Manganese
0.6
1.4
Zinc
0.4
5.8
Copper
T
0.4
Nitrate
10
*
pH
6.3
7.9
Substance
The concentration of phloem sap fluctuates in
ranging from 8 to 20%. 90% or more
phloem juice consists of carbohydrates, mainly
from the disaccharide sucrose (C12H22011).
In some species, along with sucrose
transport form of carbohydrates are:
oligosugar (raffinose, verbascose, stachyose)
– Birch, Malvaceae, Elm, Cucurbita
some alcohols (mannitol - olive,
sorbitol - rosaceous, dulcite Euonymous). Monosaccharides (glucose and
fructose) make up a small proportion
moving carbohydrates.
Nitrogenous substances are transported through
phloem in the form of amino acids and amides. In
phloem sap found low molecular weight
proteins, organic acids, phytohormones,
vitamins, inorganic ions.
Distinctive feature
phloem sap is
slightly alkaline reaction (pH = 8.08.5), high concentration of ATP
and K+ ions.

Features of movement along the phloem

High speed - 50-100 cm / h (according to
simplast 6 cm/hour).
Lots of material to carry.
During the growing season down the trunk
can pass 250 kg of sugar.
Transfer over long distances - up to 100 m.
The relative mass of the phloem is not large.
The sieve tubes are very thin - diameter 30
microns (hair thickness - 60-71 microns).

Influence of environmental conditions

The transport of substances through the phloem depends on:
from temperature. The optimum temperature is 20 and 30 0C.
conditions of mineral nutrition (boron, phosphorus, potassium
speed up the movement of sucrose).
water
connection with metabolism: inhibited in the presence of all
metabolic inhibitors (sodium azide, iodoacetate,
dinitrophenol, etc.) and is accelerated by the addition of ATP.

The mechanism of phloem transport

Hypothesis of "mass current"
Put forward in 1930 by E. Munch.
Assimilates are transported from
source (A) to the place
consumption (B) gradient
turgor pressure,
resulting
osmosis.
Between B and A is created
osmotic gradient, which
in ST turns into a gradient
hydrostatic pressure. AT
as a result, in the phloem arises
liquid current suppression from
leaf to the root.

Electroosmotic flow hypothesis

Nominated in 1979 by D. Spanner
On each sieve plate, there is
electrical potential associated with
circulation of K+ ions.
K + is active (with the expenditure of ATP energy)
absorbed above the sieve
septum and penetrates through it into
lower segment.
On the other side of the partition, K+ ions
passively go into the escort
cell. Active intake of K+ with
one side of the sieve tube
ensured that
assimilation flow enriches
sieve tube of ATP.
Occurs on each sieve
plate electric potential and
is the driving force of the flow
sucrose by phloem.

Phloem unloading

The H+ pump operates in the acceptor plasmalemma. H+ are pumped out (apoplast
acidified), which contributes to the return of K + and sucrose. ΔрН occurs, which leads to
to the intake of H+ in the symport with sucrose (H+ along the gradient, sucrose against).
Acceptor
free
space
H+-pump
Cellmate
H+
H+
sucrose
K+
sucrose

Continuous circulation of the internal water environment is an essential attribute of life

Structural and functional relationships between ascending
and
descending
water
streams
provide
functioning of a unified hydrodynamic system in
plants.
Similarity to the open circulatory system of animals

Since all three main groups of organic substances are closely related in metabolism, two main key points in their interconversion can be distinguished. It is primarily education pyruvic acid and acetic acid. It is these two substances that are the cornerstones on which the cycles of carbohydrates, fats and proteins are based.

From pyruvic acid the pathways for the formation of glucose, and, consequently, glucose-1-phosphate, as the basis for the formation of carbohydrates, and the formation of organic acids (keto acids), which begin the pathway for the synthesis of amino acids, depart.

Acetic acid, formed in line with the synthesis of organic acids from pyruvic acid, is the beginning of the path for the formation of fats, and in line with the breakdown of fatty acids as a result of oxidation, it is a link between the metabolism of fats and carbohydrates.

The formation of nucleic acids, various secondary organic compounds is based on substances synthesized at the intermediate stages of the synthesis of these three groups of substances.

Movement of organic matter in a plant

In a plant, the leaf is the main organ of biosynthesis. The products of photosynthesis are stored in the form of starch in chloroplasts and leukoplasts, the redistribution of carbohydrates occurs when starch passes into soluble simple sugars.

in plant xylem serves to move water and minerals from the soil to the aboveground part, and phloem serves to deliver sucrose from the leaves to other parts of the plant.

By phloem the outflow of substances is observed from the donor (organ-synthesizer) up and down- to any acceptor organ where these substances are stored or consumed. Organs that accept substances are, as a rule, storage organs (root crops, rhizomes, tubers, bulbs).

By xylem the substances move only down up.

All consuming organs are provided, as a rule, by the nearest donor. The upper photosynthetic showers supply the growing buds and the youngest leaves. The lower leaves provide the roots. The fruits are provided from the leaves closest to them.

Transport along the phloem can occur simultaneously in two directions. This " bidirectionality"is the result unilateral current in separate but adjacent sieve tubes connected to various donors and acceptors.

Sieve tubes are thin-walled elongated cells connected at their ends and forming a continuous tube. Cell walls are pierced at points of contact sieve pores and that's why they're called sieve plates. Unlike xylem sieve cells phloem cells - live, although they are unlike ordinary living cells. They do not have a nucleus, but contain some other organelles and a plasmalemma that plays an important role in keeping sugars in the sieve tubes. The ability of phloem cells to plasmolysis can serve as proof. Sieve tubes have a short lifespan and are constantly replaced by new ones formed during the division of the cambium.

The movement of substances through the phloem occurs at a high speed: up to 100 cm / h. Transport along the phloem is carried out by the flow of solutions. The high hydrostatic pressure caused by the movement of water into sugar-rich areas with a high negative water potential causes solutions to flow into areas of lower pressure. Removing the sugar from them ensures that there is always a gradient and therefore a flow of the solution. Solute loading includes co-transport ( cotransport) sucrose and hydrogen ions with the participation of a specific permease. This process is driven by an acidity gradient and an electrochemical gradient. The absorbed hydrogen ions are subsequently released using a proton transporter that uses the energy of ATP.

In addition to sucrose, amino acids and amides (asparagine, glutamine) are transported in the phloem stream; during aging, organic and mineral substances from dying organs are also added.

Three systems are mainly involved in the directed transport of assimilates in the plant:

pushing or forcing (sheet),

conductive (phloem),

attracting or attracting (meristematic and storage tissues).

Thus, the movement of substances in a plant includes a complex set of processes of apiary movement through the xylem and phloem, which is regulated by the plant and depends both on external factors and on the phase of plant development.