Many people almost know what plastids are,school bench. In the course of botany, it is said that in plant cells, plastids can be of various shapes, sizes, and perform various functions in the cell. This article will remind you of the structure of plastids, their types and functions to those who have graduated from school long ago, and will be useful to everyone who is interested in biology.
The picture below schematically showsthe structure of plastids in the cell. Regardless of its kind, it has an external and internal membrane performing a protective function, a stroma - an analogue of the cytoplasm, a ribosome, a DNA molecule, enzymes.
In chloroplasts there are special structures - granules. Granas are formed from thylakoids - structures that resemble discs. Thylakoids are involved in the synthesis of ATP and oxygen.
In chloroplasts, as a result of photosynthesis, starch grains are formed.
Leukoplasts are not pigmented. They do not have tilakoids, they do not participate in photosynthesis. Most of the leukoplasts are concentrated in the stalk and root of the plant.
Chromoplasts have in their composition lipid droplets - structures containing lipids, necessary to supply the structure of plastids with additional energy.
Plastids can be of different colors, sizes and shapes. Their dimensions range from 5 to 10 μm. The form is usually oval or round, but it can be any other.
Plastids can be colorless (leukoplasts), green (chloroplasts), yellow or orange (chromoplasts). It is the chloroplasts that give the leaves of plants a green color.
Another variety of plastids, chromoplasts, is responsible for yellow, red or orange coloration.
Colorless plastids in the cell functionstorage of nutrients. Leukoplasts contain fats, starch, proteins and enzymes. When the plant needs additional energy, the starch is split into monomers - glucose.
Leukoplasts under certain conditions (underthe action of sunlight or the addition of chemicals) can be converted into chloroplasts, chloroplasts are converted to chromoplasts when chlorophyll is destroyed, and the coloring pigments of chromoplasts - carotene, anthocyan or xanthophyll - predominate in color. This transformation is noticeable in the autumn, when leaves and many fruits change color due to the destruction of chlorophyll and the manifestation of chromoplast pigments.
As mentioned above, plastids can be different, and their functions in the plant cell depend on the variety.
Leukoplasts serve mainly for storage of nutrients and maintenance of vital activity of a plant due to ability to store and synthesize proteins, lipids, enzymes.
Chloroplasts play a key role in the processphotosynthesis. With the participation of chlorophyll concentrated in plastids, carbon dioxide and water molecules are converted into glucose and oxygen molecules.
Chromoplasts, due to their bright color, attract insects to pollinate plants. The study of the functions of these plastids is still ongoing.
