One of the distinguishing features of representatives of the vegetable kingdom is the presence in their cells of special structures - plastids. These include chloroplasts, chromoplasts and leukoplasts, the structure and functions of which will be discussed in our article.
What is plastids?
Plastids are called organelles of plant cells, fungi and some protozoa. It is a round-shaped bull, which has a semi-autonomous structure. They are able to mutually convert into each other. For example, leykoplasty, the structure and functions of which change under the influence of direct sunlight, are transformed into chloroplasts. Many observed that potato tubers are greener. This is the result of such an amazing transformation. But to use such a product in food is not worth it. Together with chloroplasts, the poison accumulates in the tubers - the alkaloid solanine. It can cause severe food poisoning and is especially dangerous for children.
When ripening fruits and vegetables, the plastids are also mutually transformed. Only in this case chromoplasts are formed from leukoplasts, which determine the color of various parts of the plant: yellow, red, pink, violet, etc.
Types of plastids
Leukoplasts, plastids of chromoplasts, chloroplasts differ both in their structure and in their functions. But they all play an important and irreplaceable role. The ability to impart color to different parts of the plant is due to the fact that chromoplasts contain different pigments - coloring substances.
The bright petals of the corollas of most plants are typical proof of this. This color, along with the aroma of flowers, attracts insects for pollination, which precedes fertilization and the formation of fruits.
Green plastids contain the chlorophyll pigment, which determines their color. The presence of this substance (along with carbon dioxide, water and solar radiation) is a prerequisite for the process of photosynthesis. In its course the plants form carbohydrates and oxygen. The first are for them a source of nutrition, growth and development. And oxygen gas all living things, from bacteria to humans, are used for breathing.
Structure of leukoplasts
Leukoplasts are colorless organelles. They have a regular spherical shape. The membrane system inside is rather weakly developed. The form can be changed to incorrect only in the case when sufficiently large starch grains start to form in their cytoplasm. Plastids of leukoplasts are contained in the plant's underlying plant tissue. It forms the basis of the modification of the shoot - tubers, bulbs, rhizomes. The function of leukoplasts is determined by such features of their structure. Many valuable nutrients can accumulate in the cavity of these organelles. Leukoplasts, like all plastids, are two-membrane organelles. However, the inner shell does not form a pronounced outgrowth inside the structure.
Leukoplasts are eukaryotic cells. This means that in their cytoplasm, DNA molecules carrying genetic information are contained in a decorated nucleus.
Function of leukoplasts
These plastids are specialized. Depending on the species, they are able to accumulate and synthesize various types of organic substances. For example, carbohydrate starch contains amyloplasts. This substance is characteristic of all plants, because it is formed from glucose obtained in the process of photosynthesis. Oleoplasty produces and stores fats. Liquid fats are also found in the cells of certain plants and are called oils. Proteinoplasts contain proteins. It is the structure of leukoplasts that determines such functions. In addition to the cavity necessary for the storage and storage of various substances, they contain enzymes. These biological natural catalysts are capable of accelerating chemical reactions, but are not part of their products. Under the influence of, for example, a simple glucose carbohydrate, a starch polysaccharide is formed. When conditions unfavorable for the course of photosynthesis arise, it is again split up into monomers and used by the plant to carry out life processes.
Where are the leukoplasts
Since the main function of leukoplasts is the accumulation of substances, these organelles are contained in thickened and fleshy parts of plants. They are especially rich in potato tubers. Each schoolboy is able to conduct a qualitative reaction to the starch that is contained in his leukoplasts. To do this, you just need to apply a few drops of iodine solution to a fresh cut. Under its influence, colorless before this plastids will acquire a rich violet color. They can be viewed under a microscope even at low magnification.
In the bulbs of plants there are also many leukoplasts. Thanks to a large supply of water and carbohydrates, such roots can tolerate unfavorable periods of drought, frost and heat under the earth. At the same time, the aboveground part of the plant dies off, and the modified shoot remains viable. For example, tulips for a couple of weeks have time to grow and fade. And further in their bulb accumulate carbohydrates, formed in the process of photosynthesis by the green parts of this spring plant.
The rhizomes are no exception. Everyone knows how difficult it is to get rid of weeds. They are not afraid of even the strongest drought, and the leaves appear again above the surface of the soil. The thing is that the plant itself develops under the ground in the form of a thickened modified shoot with elongated interstices. It contains a significant amount of leukoplasts, and therefore a stock of substances.
Endosperm seeds, spores of fungi, ovules of higher plants perform their functions precisely due to the presence of these plastids.
Origin of leukoplasts
The fact of the presence of leukoplasts even in the embryonic tissue of plant organisms is proved. And they are formed from the so-called proplastids. These structures are the precursors of all kinds of similar organelles. Initially, they are located in the meristem - the educational tissue of plants. Proplastids are microscopic bodies up to 1 μm in size. It is with them that the whole chain of interconversion of these organelles of plant cells begins.
Thus, the main function of leukoplasts is the synthesis, accumulation and storage of various types of organic substances necessary for the existence of living organisms.