One of the distinguishing features of representatives of the plant 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 are plastids
Plastids are called organelles of cells of plants, fungi and some protozoa. These are rounded bodies that have a semi-autonomous structure. They are able to transform into each other. For example, leukoplasts, whose structure and functions change under the influence of direct sunlight, are converted into chloroplasts. Many have observed that potato tubers turn green. This is the result of such an amazing transformation. But you should not eat such a product. Together with chloroplasts, poison accumulates in the tubers - the alkaloid solanine. It can cause severe food poisoning and is especially dangerous for children.
When fruits and vegetables ripen, plastids also interconvert. Only in this case, chromoplasts are formed from leukoplasts, which determine the color of variousplant parts: yellow, red, pink, purple, etc.
Plastid types
Leucoplasts, plastids, chromoplasts, chloroplasts differ in both structure and functions. But they all play an important and irreplaceable role. The ability to give color to various parts of the plant is due to the fact that chromoplasts contain various pigments - dyes.
The bright petals of the corollas of most plants are typical proof of this. This color, along with the fragrance of the flowers, attracts insects for pollination, which precedes fertilization and fruit formation.
Green plastids contain the pigment chlorophyll, which determines their color. The presence of this substance (along with carbon dioxide, water and solar radiation) is a prerequisite for the flow of the photosynthesis process. In its course, plants form carbohydrates and oxygen. The first are for them a source of nutrition, growth and development. And oxygen gas is used by all living beings, from bacteria to humans, for breathing.
The structure of leukoplasts
Leucoplasts are colorless organelles. They have the correct spherical shape. The membrane system inside is rather poorly developed. The shape can change to incorrect only when sufficiently large starch grains begin to form in their cytoplasm. Plastids leukoplasts are found in the storage basic tissue of plants. It forms the basis of modifications of the shoot - tubers, bulbs, rhizomes. The function of leukoplasts is determined by such featurestheir buildings. Many valuable nutrients can accumulate in the cavity of these organelles. Leucoplasts, like all plastids, are two-membrane organelles. However, the inner shell does not form pronounced outgrowths inside the structure.
Leukoplasts are eukaryotic cells. This means that in their cytoplasm, DNA molecules that carry genetic information are contained in a well-formed 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, the carbohydrate starch contains amyloplasts. This substance is characteristic of all plants, since it is formed from glucose obtained during photosynthesis. Oleoplasts produce and store fats. Liquid fats are also found in the cells of some 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 supply 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 carbohydrate, glucose, the polysaccharide starch is formed. When conditions unfavorable for photosynthesis occur, it is again broken down into monomers and used by the plant to carry out vital processes.
Where are the leukoplasts
BecauseThe main function of leukoplasts is the accumulation of substances; these organelles are found in the thickened and fleshy parts of plants. Potato tubers are especially rich in them. Each student is able to conduct a qualitative reaction to the starch 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, previously colorless plastids will acquire a rich purple color. They can be seen under a microscope even at low magnification.
There are also many leucoplasts in plant bulbs. Due to the large supply of water and carbohydrates, such roots are able to endure unfavorable periods of drought, frost and heat underground. In this case, the above-ground small part of the plant dies off, and the modified shoot remains viable. For example, tulips have time to grow and bloom in a couple of weeks. And then in their bulb accumulate carbohydrates formed in the process of photosynthesis by the green parts of this spring plant.
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 soil surface. The thing is that the plant itself develops underground in the form of a thickened modified shoot with elongated internodes. It contains a significant amount of leukoplasts, and therefore a supply of substances.
Seed endosperm, fungal spores, eggs of higher plants perform their functions precisely due to the presence of these plastids.
Originleucoplasts
The fact of the presence of leukoplasts in the embryonic tissue of plant organisms has been proven. 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 from them that the whole chain of mutual transformations 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.
