Features of the structure of plastids. Types, structure and functions of plastids What is a plastid

, brown, yellow-green, diatoms) membranes are considered the result of two- and three-fold endosymbiosis, respectively.

General features of the structure of plastids of higher plants

Typical plastids of higher plants are surrounded by a shell of two membranes - external and internal. The inner and outer membranes of plastids are poor in phospholipids and enriched in galactolipids. The outer membrane has no folds, never fuses with the inner membrane and contains a pore protein that provides free transport of water, ions and metabolites with a mass of up to 10 kDa. The outer membrane has areas of close contact with the inner membrane; it is assumed that in these areas the transport of proteins from the cytoplasm at the beginning of plastids occurs. The inner membrane is permeable to small uncharged molecules and to undissociated low molecular weight monocarboxylic acids; for larger and charged metabolites, protein carriers are localized in the membrane. The stroma - the internal contents of plastids - is a hydrophilic matrix containing inorganic ions, water-soluble organic metabolites, the plastid genome (several copies of circular DNA), prokaryotic-type ribosomes, matrix synthesis enzymes and other enzymatic systems. The endomembrane system of plastids develops as a result of the detachment of vesicles from the inner membrane and their ordering. The degree of development of the endomembrane system depends on the type of plastid. The endomembrane system reaches its greatest development in chloroplasts, where it is the site of light reactions of photosynthesis and is represented by free stromal thylakoids and thylakoids collected in stacks - grana. The inner space of endomembranes is called the lumen. The thylakoid lumen, like the stroma, contains a number of water-soluble proteins.

Genome and protein synthesizing system of plastids of higher plants

One of the evidence for the origin of plastids from ancient cyanobacteria is the similarity of their genomes, although the plastid genome (plastome) is much smaller. The layer of higher plants is represented by multicopy circular double-stranded DNA (plDNA) ranging in size from 75 to 290 thousand bp. Most plastid genomes contain two inverted repeats (IR A and IR B), dividing the DNA molecule into two unique regions: large (LSR) and small (SSR). The inverted repeats contain the genes of all four rRNAs (4.5S, 5S, 16S and 23S) that are part of plastid ribosomes, as well as the genes of some tRNAs. Gymnosperms and legumes do not contain inverted repeats. Many plastid genes are organized into operons, groups of genes read from a common promoter. Some plastid genes have an exon-intron structure. Plastids encode genes that serve the processes of transcription and translation (housekeeping genes), as well as some genes that ensure the functions of plastids in the cell, primarily photosynthesis.

Transcription in plastids is provided by two types of RNA polymerases:

1. Multisubunit plastid RNA polymerase of the bacterial type consists of two α-subunits and one β, β", β" (all of these subunits are encoded in the plastid genome). However, its activation requires the presence of the σ-subunit, which is encoded in the nucleus of the plant cell and imported into plastids upon illumination. Thus, plastid RNA polymerase is active only in light. Plastid RNA polymerase can provide transcription from genes with eubacterial promoters (most genes for photosynthetic proteins), as well as from genes with universal promoters.
2. Monomeric RNA polymerase of the phage type is encoded in the nucleus and the protein has a special signal sequence that ensures import into plastids. Provides transcription of housekeeping genes (in particular, the genes of the rif operon, which contains the genes for plastid RNA polymerase).

The process of maturation of plastid transcripts has its own characteristics. In particular, plastid introns are capable of autosplicing, that is, excision of introns occurs autocatalytically. In addition, RNA editing occurs in plastids - a chemical modification of RNA bases, leading to a change in the encoded information (most often, cytidine is replaced by uridine). Most mature plastid mRNAs contain a hairpin in the 3" non-coding region, which protects it from ribonucleases.

• Chloroplasts- green plastids whose main function is photosynthesis. Chloroplasts usually have an ellipse shape and a length of 5 to 8 microns. The number of chloroplasts in a cell is different: the chlorenchyma cell of the Arabidopsis leaf contains about 120 chloroplasts, the spongy chlorenchyma of the castor bean leaf contains about 20, and the cell of the filamentous seaweed Spirogyra contains a single ribbon-shaped chloroplast. Chloroplasts have a well-developed endomembrane system, in which thylakoid stroma and stacks of thylakoids - grana are distinguished. The green color of chloroplasts is due to the high content of the main pigment of photosynthesis - chlorophyll. In addition to chlorophyll, chloroplasts contain various carotenoids. The set of pigments involved in photosynthesis (and, accordingly, color) is different among representatives of different taxa.
• Chromoplasts- plastids colored yellow, red or orange. Chromoplasts can develop from proplastids or redifferentiate from chloroplasts; chromoplasts can also redifferentiate into chloroplasts. The color of chromoplasts is associated with the accumulation of carotenoids in them. Chromoplasts determine the color of autumn leaves, petals of some flowers (buttercups, marigolds), root vegetables (carrots), and ripened fruits (tomato).

Write a review about the article "Plastids"

Links

Organelles Cell wall Substances Structures Division plant cell Special stages Structures

Endomembrane system Cytoskeleton Endosymbionts Other internal organelles External organelles

Excerpt characterizing Plastids

The drone sighed without answering.
“If you order, they will leave,” he said.
“No, no, I’ll go to them,” said Princess Marya
Despite the dissuading of Dunyasha and the nanny, Princess Marya went out onto the porch. Dron, Dunyasha, the nanny and Mikhail Ivanovich followed her. “They probably think that I am offering them bread so that they will remain in their places, and I will leave myself, abandoning them to the mercy of the French,” thought Princess Marya. - I will promise them a month in an apartment near Moscow; I’m sure Andre would have done even more in my place,” she thought, approaching the crowd standing in the pasture near the barn in the twilight.
The crowd, crowded, began to stir, and their hats quickly came off. Princess Marya, with her eyes downcast and her feet tangling in her dress, came close to them. So many different old and young eyes were fixed on her and there were so many different faces that Princess Marya did not see a single face and, feeling the need to suddenly talk to everyone, did not know what to do. But again the consciousness that she was the representative of her father and brother gave her strength, and she boldly began her speech.
“I’m very glad that you came,” Princess Marya began, without raising her eyes and feeling how quickly and strongly her heart was beating. “Dronushka told me that you were ruined by the war.” This is our common grief, and I will not spare anything to help you. I’m going myself, because it’s already dangerous here and the enemy is close... because... I give you everything, my friends, and I ask you to take everything, all our bread, so that you don’t have any need. And if they told you that I am giving you bread so that you can stay here, then this is not true. On the contrary, I ask you to leave with all your property to our Moscow region, and there I take it upon myself and promise you that you will not be in need. They will give you houses and bread. - The princess stopped. Only sighs were heard in the crowd.
“I’m not doing this on my own,” the princess continued, “I’m doing this in the name of my late father, who was a good master to you, and for my brother and his son.”
She stopped again. No one interrupted her silence.
- Our grief is common, and we will divide everything in half. “Everything that is mine is yours,” she said, looking around at the faces standing in front of her.
All eyes looked at her with the same expression, the meaning of which she could not understand. Whether it was curiosity, devotion, gratitude, or fear and distrust, the expression on all faces was the same.
“Many are pleased with your mercy, but we don’t have to take the master’s bread,” said a voice from behind.
- Why not? - said the princess.
No one answered, and Princess Marya, looking around the crowd, noticed that now all the eyes she met immediately dropped.
- Why don’t you want to? – she asked again.
Nobody answered.
Princess Marya felt heavy from this silence; she tried to catch someone's gaze.
- Why don’t you talk? - the princess turned to the old man, who, leaning on a stick, stood in front of her. - Tell me if you think anything else is needed. “I’ll do everything,” she said, catching his gaze. But he, as if angry at this, lowered his head completely and said:
- Why agree, we don’t need bread.
- Well, should we give it all up? We don't agree. We don’t agree... We don’t agree. We feel sorry for you, but we do not agree. Go on your own, alone...” was heard in the crowd from different directions. And again the same expression appeared on all the faces of this crowd, and now it was probably no longer an expression of curiosity and gratitude, but an expression of embittered determination.
“You didn’t understand, right,” said Princess Marya with a sad smile. - Why don’t you want to go? I promise to house you and feed you. And here the enemy will ruin you...
But her voice was drowned out by the voices of the crowd.
“We don’t have our consent, let him ruin it!” We don’t take your bread, we don’t have our consent!
Princess Marya again tried to catch someone's gaze from the crowd, but not a single glance was directed at her; the eyes obviously avoided her. She felt strange and awkward.
- See, she taught me cleverly, follow her to the fortress! Destroy your home and go into bondage and go. Why! I'll give you the bread, they say! – voices were heard in the crowd.
Princess Marya, lowering her head, left the circle and went into the house. Having repeated the order to Drona that there should be horses for departure tomorrow, she went to her room and was left alone with her thoughts.

For a long time that night, Princess Marya sat at the open window in her room, listening to the sounds of men talking coming from the village, but she did not think about them. She felt that no matter how much she thought about them, she could not understand them. She kept thinking about one thing - about her grief, which now, after the break caused by worries about the present, had already become past for her. She could now remember, she could cry and she could pray. As the sun set, the wind died down. The night was quiet and fresh. At twelve o'clock the voices began to fade, the rooster crowed, the full moon began to emerge from behind the linden trees, a fresh, white mist of dew rose, and silence reigned over the village and over the house.
One after another, pictures of the close past appeared to her - illness and her father’s last minutes. And with sad joy she now dwelled on these images, driving away from herself with horror only one last image of his death, which - she felt - she was unable to contemplate even in her imagination at this quiet and mysterious hour of the night. And these pictures appeared to her with such clarity and with such detail that they seemed to her now like reality, now the past, now the future.
Then she vividly imagined that moment when he had a stroke and was dragged out of the garden in the Bald Mountains by the arms and he muttered something with an impotent tongue, twitched his gray eyebrows and looked at her restlessly and timidly.
“Even then he wanted to tell me what he told me on the day of his death,” she thought. “He always meant what he told me.” And so she remembered in all its details that night in Bald Mountains on the eve of the blow that happened to him, when Princess Marya, sensing trouble, remained with him against his will. She did not sleep and at night she tiptoed downstairs and, going up to the door to the flower shop where her father spent the night that night, listened to his voice. He said something to Tikhon in an exhausted, tired voice. He obviously wanted to talk. “And why didn’t he call me? Why didn’t he allow me to be here in Tikhon’s place? - Princess Marya thought then and now. “He will never tell anyone now everything that was in his soul.” This moment will never return for him and for me, when he would say everything he wanted to say, and I, and not Tikhon, would listen and understand him. Why didn’t I enter the room then? - she thought. “Maybe he would have told me then what he said on the day of his death.” Even then, in a conversation with Tikhon, he asked about me twice. He wanted to see me, but I stood here, outside the door. He was sad, it was hard to talk with Tikhon, who did not understand him. I remember how he spoke to him about Lisa, as if she were alive - he forgot that she died, and Tikhon reminded him that she was no longer there, and he shouted: “Fool.” It was hard for him. I heard from behind the door how he lay down on the bed, groaning, and shouted loudly: “My God! Why didn’t I get up then?” What would he do to me? What would I have to lose? And maybe then he would have been consoled, he would have said this word to me.” And Princess Marya said out loud the kind word that he said to her on the day of his death. “Darling! - Princess Marya repeated this word and began to sob with tears that relieved her soul. She now saw his face in front of her. And not the face that she had known since she could remember, and which she had always seen from afar; and that face - timid and weak, which on the last day, bending down to his mouth to hear what he said, she examined up close for the first time with all its wrinkles and details.
“Darling,” she repeated.
“What was he thinking when he said that word? What is he thinking now? - suddenly a question came to her, and in response to this she saw him in front of her with the same expression on his face that he had in the coffin, on his face tied with a white scarf. And the horror that gripped her when she touched him and became convinced that it was not only not him, but something mysterious and repulsive, gripped her now. She wanted to think about other things, wanted to pray, but could do nothing. She looked with large open eyes at the moonlight and shadows, every second she expected to see his dead face and felt that the silence that stood over the house and in the house shackled her.
- Dunyasha! – she whispered. - Dunyasha! – she screamed in a wild voice and, breaking out of the silence, ran to the girls’ room, towards the nanny and girls running towards her.

On August 17, Rostov and Ilyin, accompanied by Lavrushka, who had just returned from captivity, and the messenger hussar, from their Yankovo ​​camp, fifteen miles from Bogucharovo, went horseback riding - to try a new horse, bought by Ilyin, and to find out if there was any hay in the villages.
Bogucharovo had been located for the last three days between two enemy armies, so that the Russian rearguard could have entered there just as easily as the French vanguard, and therefore Rostov, as a caring squadron commander, wanted to take advantage of the provisions that remained in Bogucharovo before the French.
Rostov and Ilyin were in the most cheerful mood. On the way to Bogucharovo, to the princely estate with an estate, where they hoped to find large servants and pretty girls, they either asked Lavrushka about Napoleon and laughed at his stories, or drove around, trying Ilyin’s horse.
Rostov neither knew nor thought that this village to which he was traveling was the estate of that same Bolkonsky, who was his sister’s fiancé.
Rostov and Ilyin released the horses for the last time to drive the horses into the drag in front of Bogucharov, and Rostov, having overtaken Ilyin, was the first to gallop into the street of the village of Bogucharov.
“You took the lead,” said the flushed Ilyin.
“Yes, everything is forward, and forward in the meadow, and here,” answered Rostov, stroking his soaring bottom with his hand.
“And in French, your Excellency,” Lavrushka said from behind, calling his sled nag French, “I would have overtaken, but I just didn’t want to embarrass him.”
They walked up to the barn, near which stood a large crowd of men.
Some men took off their hats, some, without taking off their hats, looked at those who had arrived. Two long old men, with wrinkled faces and sparse beards, came out of the tavern and, smiling, swaying and singing some awkward song, approached the officers.
- Well done! - Rostov said, laughing. - What, do you have any hay?
“And they are the same...” said Ilyin.
“Vesve...oo...oooo...barking bese...bese...” the men sang with happy smiles.
One man came out of the crowd and approached Rostov.
- What kind of people will you be? – he asked.
“The French,” Ilyin answered, laughing. “Here is Napoleon himself,” he said, pointing to Lavrushka.
- So, you will be Russian? – the man asked.
- How much of your strength is there? – asked another small man, approaching them.
“Many, many,” answered Rostov. - Why are you gathered here? - he added. - A holiday, or what?
“The old people have gathered on worldly business,” the man answered, moving away from him.
At this time, along the road from the manor's house, two women and a man in a white hat appeared, walking towards the officers.
- Mine in pink, don’t bother me! - said Ilyin, noticing Dunyasha resolutely moving towards him.
- Ours will be! – Lavrushka said to Ilyin with a wink.
- What, my beauty, do you need? - Ilyin said, smiling.
- The princess ordered to find out what regiment you are and your last names?

Plastids are organelles specific to plant cells (they are present in the cells of all plants, with the exception of most bacteria, fungi and some algae).

The cells of higher plants usually contain from 10 to 200 plastids 3-10 µm in size, most often having the shape of a biconvex lens. In algae, green plastids, called chromatophores, are very diverse in shape and size. They can have star-shaped, ribbon-shaped, mesh and other shapes.

There are 3 types of plastids:

• Colorless plastids - leucoplasts;
• painted - chloroplasts(green);
• painted - chromoplasts(yellow, red and other colors).

These types of plastids are to a certain extent capable of transforming into each other - leucoplasts, with the accumulation of chlorophyll, turn into chloroplasts, and the latter, with the appearance of red, brown and other pigments, into chromoplasts.

Structure and functions of chloroplasts

Chloroplasts are green plastids containing a green pigment - chlorophyll.

The main function of chloroplast is photosynthesis.

Chloroplasts have their own ribosomes, DNA, RNA, fat inclusions, and starch grains. The outside of the chloroplast is covered with two protein-lipid membranes, and small bodies - grana and membrane channels - are immersed in their semi-liquid stroma (ground substance).

Grans(about 1 µm in size) - packets of round flat sacs (thylakoids), folded like a column of coins. They are located perpendicular to the surface of the chloroplast. The thylakoids of neighboring grana are connected to each other by membrane channels, forming a single system. The number of grana in chloroplasts varies. For example, in spinach cells, each chloroplast contains 40-60 grains.

Chloroplasts inside the cell can move passively, carried away by the current of the cytoplasm, or actively move from place to place.

• If the light is very intense, they turn edge-on towards the bright rays of the sun and line up along the walls parallel to the light.
• In low light, chloroplasts move to the cell walls facing the light and turn their large surface towards it.
• In average illumination they occupy an average position.

This achieves the most favorable lighting conditions for the photosynthesis process.

Chlorophyll

The grana of plant cell plastids contain chlorophyll, packaged with protein and phospholipid molecules to provide the ability to capture light energy.

The chlorophyll molecule is very similar to the hemoglobin molecule and differs mainly in that the iron atom located in the center of the hemoglobin molecule is replaced in chlorophyll by a magnesium atom.

There are four types of chlorophyll found in nature: a, b, c, d.

Chlorophylls a and b contain higher plants and green algae, diatoms contain a and c, red algae contain a and d.

Chlorophylls a and b have been studied better than others (they were first separated by the Russian scientist M.S. Tsvet at the beginning of the 20th century). In addition to them, there are four types of bacteriochlorophylls - green pigments of purple and green bacteria: a, b, c, d.

Most photosynthetic bacteria contain bacteriochlorophyll a, some contain bacteriochlorophyll b, and green bacteria contain c and d.

Chlorophyll has the ability to absorb solar energy very efficiently and transfer it to other molecules, which is its main function. Thanks to this ability, chlorophyll is the only structure on Earth that ensures the process of photosynthesis.

The main function of chlorophyll in plants is to absorb light energy and transfer it to other cells.

Plastids, like mitochondria, are characterized to some extent by autonomy within the cell. They reproduce by fission.

Along with photosynthesis, the process of protein biosynthesis occurs in plastids. Due to their DNA content, plastids play a role in the transmission of traits by inheritance (cytoplasmic inheritance).

Structure and functions of chromoplasts

Chromoplasts belong to one of the three types of plastids of higher plants. These are small, intracellular organelles.

Chromoplasts have different colors: yellow, red, brown. They give a characteristic color to ripe fruits, flowers, and autumn foliage. This is necessary to attract pollinating insects and animals that feed on fruits and distribute seeds over long distances.

The structure of the chromoplast is similar to other plastids. The inner shells of the two are poorly developed, sometimes completely absent. The protein stroma, DNA and pigment substances (carotenoids) are located in a limited space.

Carotenoids are fat-soluble pigments that accumulate in the form of crystals.

The shape of chromoplasts is very diverse: oval, polygonal, needle-shaped, crescent-shaped.

The role of chromoplasts in the life of a plant cell is not fully understood. Researchers suggest that pigment substances play an important role in redox processes and are necessary for the reproduction and physiological development of cells.

Structure and functions of leukoplasts

Leukoplasts are cell organelles in which nutrients accumulate. The organelles have two shells: a smooth outer shell and an inner one with several protrusions.

Leukoplasts turn into chloroplasts in the light (for example, green potato tubers); in their normal state they are colorless.

The shape of the leukoplasts is spherical and regular. They are found in the storage tissue of plants, which fills the soft parts: the core of the stem, root, bulbs, leaves.

The functions of leukoplasts depend on their type (depending on the accumulated nutrient).

Types of leukoplasts:

1. Amyloplasts accumulate starch and are found in all plants, since carbohydrates are the main food product of the plant cell. Some leucoplasts are completely filled with starch; they are called starch grains.
2. Elaioplasts produce and store fats.
3. Proteinoplasts contain proteins.

Leukoplasts also serve as an enzymatic substance. Under the influence of enzymes, chemical reactions proceed faster. And in an unfavorable period of life, when photosynthesis processes are not carried out, they break down polysaccharides into simple carbohydrates, which plants need to survive.

Photosynthesis cannot occur in leucoplasts because they do not contain grains or pigments.

Plant bulbs, which contain many leucoplasts, can tolerate long periods of drought, low temperatures, and heat. This is due to large reserves of water and nutrients in the organelles.

The precursors of all plastids are proplastids, small organelles. It is assumed that leuco- and chloroplasts are capable of transforming into other species. Ultimately, after fulfilling their functions, chloroplasts and leucoplasts become chromoplasts - this is the last stage of plastid development.

Important to know! Only one type of plastid can be present in a plant cell at a time.

Summary table of the structure and functions of plastids

Properties	Chloroplasts	Chromoplasts	Leukoplasts
Structure	Double-membrane organelle, with grana and membranous tubules	Organelle with an undeveloped internal membrane system	Small organelles found in parts of the plant hidden from light
Color	Greens	Multicolored	Colorless
Pigment	Chlorophyll	Carotenoid	Absent
Form	Round	Polygonal	Globular
Functions	Photosynthesis	Attracting potential plant distributors	Nutrient supply
Replaceability	Transform into chromoplasts	Do not change, this is the last stage of plastid development	Transform into chloroplasts and chromoplasts

A cell is a complex structure made up of many components called organelles. Moreover, the composition plant cell slightly different from animals, and the main difference lies in the presence plastids.

Description of cellular elements

What cell components are called plastids. These are structural cell organelles that have a complex structure and functions that are important for the life of plant organisms.

Important! Plastids are formed from proplastids, which are located inside meristem or educational cells and are much smaller in size than the mature organelle. They are also divided, like bacteria, into two halves by constriction.

Which ones do they have? plastids structure It is difficult to see under a microscope; thanks to the dense shell, they are not translucent.

However, scientists were able to find out that this organoid has two membranes, inside it is filled with stroma, a liquid similar to cytoplasm.

Folds of the inner membrane, stacked, form granules that can be connected to each other.

Also present inside are ribosomes, lipid droplets, and starch grains. Plastids, especially chloroplasts, also have their own molecules.

Classification

They are divided into three groups according to color and functions:

• chloroplasts,
• chromoplasts,
• leucoplasts.

Chloroplasts

The most deeply studied ones are green in color. Contained in plant leaves, sometimes in stems, fruits and even roots. In appearance they look like rounded grains 4-10 micrometers in size. Small size and large quantity significantly increases the working surface area.

They may vary in color, depending on the type and concentration of pigment they contain. Basic pigment - chlorophyll, xanthophyll and carotene are also present. In nature, there are 4 types of chlorophyll, designated by Latin letters: a, b, c, e. The first two types contain cells of higher plants and green algae; diatoms contain only varieties - a and c.

Attention! Like other organelles, chloroplasts are capable of aging and destruction. The young structure is capable of division and active work. Over time, their grains break down and the chlorophyll disintegrates.

Chloroplasts perform an important function: inside them the process of photosynthesis occurs— conversion of sunlight into the energy of chemical bonds of forming carbohydrates. At the same time, they can move along with the flow of cytoplasm or actively move on their own. So, in low light they accumulate near the walls of the cell with a large amount of light and turn towards it with a larger area, and in very active light, on the contrary, they stand edge-on.

Chromoplasts

They replace destroyed chloroplasts and come in yellow, red and orange shades. The color is formed due to the content of carotenoids.

These organelles are found in the leaves, flowers and fruits of plants. The shape can be round, rectangular or even needle-shaped. The structure is similar to chloroplasts.

Main function – coloring flowers and fruits, which helps attract pollinating insects and animals that eat the fruits and thereby contribute to the spread of plant seeds.

Important! Scientists are speculating about the role chromoplasts in the redox processes of the cell as a light filter. The possibility of their influence on the growth and reproduction of plants is considered.

Leukoplasts

Data plastids have differences in structure and functions. The main task is to store nutrients for future use, so they are found mainly in fruits, but can also be in thickened and fleshy parts of the plant:

• tubers,
• rhizomes,
• root vegetables,
• bulbs and others.

Colorless color does not allow you to select them in the structure of the cell, however, leukoplasts are easy to see when a small amount of iodine is added, which, interacting with starch, turns them blue.

The shape is close to round, while the membrane system inside is poorly developed. The absence of membrane folds helps the organelle in storing substances.

Starch grains increase in size and easily destroy the internal membranes of the plastid, as if stretching it. This allows you to store more carbohydrates.

Unlike other plastids, they contain a DNA molecule in a shaped form. At the same time, accumulating chlorophyll, leucoplasts can transform into chloroplasts.

When determining what function leucoplasts perform, it is necessary to note their specialization, since there are several types that store certain types of organic matter:

• amyloplasts accumulate starch;
• oleoplasts produce and store fats, while the latter can be stored in other parts of the cells;
• proteinoplasts “protect” proteins.

In addition to accumulation, they can perform the function of breaking down substances, for which there are enzymes that are activated when there is a shortage of energy or building material.

In such a situation, enzymes begin to break down stored fats and carbohydrates into monomers so that the cell receives the necessary energy.

All varieties of plastids, despite structural features, have the ability to transform into each other. Thus, leucoplasts can transform into chloroplasts; we see this process when potato tubers turn green.

At the same time, in autumn, chloroplasts turn into chromoplasts, as a result of which the leaves turn yellow. Each cell contains only one type of plastid.

Origin

There are many theories of origin, the most substantiated among them are two:

• symbiosis,
• absorption.

The first considers cell formation as a process of symbiosis occurring in several stages. During this process, heterotrophic and autotrophic bacteria unite, receiving mutual benefits.

The second theory considers the formation of cells through the absorption of smaller ones by larger organisms. However, they are not digested; they are integrated into the structure of the bacterium, performing their function within it. This structure turned out to be convenient and gave the organisms an advantage over others.

Types of plastids in a plant cell

Plastids - their functions in the cell and types

Conclusion

Plastids in plant cells are a kind of “factory” where production associated with toxic intermediates, high energy and free radical transformation processes takes place.

In this article we will take a closer look at what plastids are. All autotrophic plants have basic cytoplasmic organelles called plastids. They got their name from the Greek - plastos, which translated into Russian means “fashioned”.

So what are plastids? What are their functions? You can find the answer to these questions by reading the article to the end. To begin with, let us highlight the main function of these organelles - the synthesis of organic substances. All plastids contain their own pigment, which determines their color. If we divide them according to this quality, we can name the following three groups:

• chloroplasts;
• chromoplasts;
• leucoplasts.

Meaning

Let's now find out what significance plastids have for plant life. Their importance in photosynthesis cannot be denied, but besides this, there are other important aspects. So, among them are:

• reduction of nitrite and sulfate;
• synthesis of metabolites (this includes purines, amino acids, fatty acids, and so on);
• synthesis of ABA, gibberellins, and so on (that is, regulatory molecules);
• storage function (iron, lipids, starch).

All plastids that are found in higher plants are diverse and each of them performs its own specific function. And their set directly depends on the type of cell.

Proplastids

We figured out what plastids are. Now let's move on to the characteristics of each individual species. First on our list were proplastids.

Compared to differentiated plastids, proplastids are smaller in size (up to 1 µm), their membrane system is poorly developed (fewer ribosomes). They have deposits of phytoferritin, the function of which is to store iron.

Leukoplasts

Plastids of this species have no color. Leukoplasts perform one very important function - storage. They are small in size and found in all plant cells. Thanks to leukoplasts, the following complex compounds are reproduced:

• starch;
• fats;
• proteins.

All of them are stored in different parts of the plant (tubers, fruits, seeds). These plastids are divided into three types based on the accumulation of substances:

• amyloplasts;
• proteinoplasts;
• eleoplasts.

In telling what plastids are, we will focus on the first type of leucoplasts.

Amyloplasts

All plastids are of great importance in biology. They are able to change from one species to another. A striking example is the transformation of leucoplasts into chloroplasts. The latter are green. Many have noticed that potato tubers turn green in the light, this is precisely due to the transition of leucoplasts to chloroplasts. Why do the leaves turn yellow in the fall? It's simple, chloroplasts turn into chromoplasts due to the destruction of chlorophyll in the first.

Externally, amyloplasts are similar to proplastids. They can transform into the following forms:

• chloroplasts;
• chromoplasts.

They can be found in the storage organs of plants.

Etioplasts

These plastids are usually called dark plastids. They are chloroplasts that lack the color of the sun. Many have noticed that flowers growing in the shade have a yellowish tint to the leaves. This indicates that the plant has a high concentration of etioplasts.

If a plant grown in sunlight is moved to the shade, then the chloroplasts will gradually begin to turn into etioplasts. The more of the latter, the cloudier and sicker the plant looks.

Chloroplasts

These plastids are the most popular in the plant world. Their color is green and their sizes reach 10 microns. The main function of chloroplasts is photosynthesis. Externally, this type of plastid looks like sacs or round bodies. They include:

• proteins;
• fats;
• pigments;

It is also important to note here that in different organisms the number, structure and size of these plastids differ.

Chromoplasts

The color of chromoplasts is slightly more varied. They can be yellow, orange, red.

This variety of colors is due to the accumulation of carotenoids. Thanks to the presence of these organelles in plants, we see a luxurious palette of colors in autumn trees, and we can distinguish ripened fruit (apples, tomatoes) from unripe ones. The shades of flower petals also depend on these organelles.

Chromoplasts can take on a variety of structures - circle, polygon, or have a needle shape.

How are plant cells different from animal cells? The answer lies in the color of plants: their color depends on the pigment content in the cells. These pigments accumulate in special organelles called plastids.

in biology?

They differ from animals in the presence of chloroplasts, leucoplasts and chromoplasts. These organelles are responsible for a number of functions, among which the process of photosynthesis clearly dominates. It is the pigment contained in plant plastids that is responsible for their color.

In the cell of any eukaryotic organism, non-membrane, single-membrane and double-membrane organelles are distinguished. Plastids and mitochondria belong to the latter type of cellular structures, since they are surrounded by two layers of the CPM.

What are cell plastids? Types of plastids

1. Chloroplasts. The main double-membrane organelles of plant cells responsible for They consist of thylakoids on which photosynthetic complexes are located. The function of thylakoids is to increase the active surface of the organelle. What are green plastids? which contain green pigments - chlorophylls. There are several groups of these molecules, each of which is responsible for its own specific functions. In higher plants, chlorophyll is the most common A, which is the main acceptor of solar energy during photosynthesis.
2. Leukoplasts. Colorless plastids that perform a storage function in They can have an irregular shape, ranging from spherical to spindle-shaped. Leukoplasts often accumulate around the cell nucleus, and in a microscope they can only be detected if there are a large number of granules. Depending on the nature of the stored substance, three types of leukoplasts are distinguished. Amyloplasts serve as a container for carbohydrates that the plant wants to store until a certain point. Proteoplasts store various proteins. Oleoplasts accumulate oils and fats, which are a source of lipids. This is what a plastid is, which performs a storage function.
3. Chromoplasts. The last type of plastid, which has a characteristic yellow, orange or even red color. Chromoplasts are the final stage of chloroplast development, when chlorophyll is destroyed and only fat-soluble carotenoids remain in the plastids. Chromoplasts are found in flower petals, ripe fruits and even plant trunks. The exact meaning of these organelles is not known for sure, but it is assumed that they are a reservoir for carotenoids and also give plants a specific color. This coloring attracts pollinating insects, which promotes plant reproduction.

Leukoplasts and chromoplasts are not capable of photosynthesis. The chlorophyll in these organelles was reduced or disappeared, so their function changed dramatically.

The role of chloroplasts in the transmission of genetic information

What is not only the energy station of the cell, but also the storage of part of the cell’s hereditary information. It is presented in the form of a circular DNA molecule, which resembles the structure of a prokaryotic nucleoid. This circumstance makes it possible to assume the symbiont origin of plastids, when bacterial cells are absorbed by plant cells, losing their autonomy, but leaving some genes.

Chloroplast DNA refers to the cytoplasmic inheritance of the cell. It is transmitted only with the help of germ cells that determine the female sex. Sperms cannot transfer male plastid DNA.

Since chloroplasts are semi-autonomous organelles, many proteins are synthesized in them. Also, when dividing, these plastids independently replicate. However, most chloroplast proteins are synthesized using information from the DNA of the nucleus. This is what a plastid is from the point of view of genetics and molecular biology.

Chloroplast - the powerhouse of the cell

During photosynthesis, many biochemical reactions occur on the thylakoids of chloroplasts. Their main task is the synthesis of glucose, as well as ATP molecules. The latter carry in their chemical bonds a large amount of energy, which is vital for the cell.

What is a plastid? It is a source of energy along with mitochondria. The process of photosynthesis is divided into light and dark stages. During the light stage of photosynthesis, phosphorus residues are attached to ADP molecules, and as a result the cell receives ATP.