Many people roughly know what plastids are from school. In the course of botany, it is said that in plant cells plastids can be of different shapes, sizes and perform various functions in the cell. This article will remind about the structure of plastids, their types and functions to those who graduated from school long ago, and will be useful to everyone who is interested in biology.
Building
The picture below schematically shows the structure of plastids in a cell. Regardless of its type, it has an outer and inner membrane that perform a protective function, a stroma - an analogue of the cytoplasm, ribosomes, a DNA molecule, enzymes.
Chloroplasts contain special structures - grana. Grana are formed from thylakoids, disc-like structures. Thylakoids are involved in the synthesis of ATP and oxygen.
Chloroplasts produce starch grains as a result of photosynthesis.
Leucoplasts are not pigmented. They do not contain thylakoids, they do not take part in photosynthesis. Most of the leukoplastsconcentrated in the stem and root of the plant.
Chromoplasts contain lipid droplets - structures containing lipids necessary to supply the plastid structure with additional energy.
Plastids can be of different colors, sizes and shapes. Their sizes fluctuate within 5-10 microns. The shape is usually oval or round, but can be any other.
Plastid types
Plastids can be colorless (leucoplasts), green (chloroplasts), yellow or orange (chromoplasts). It is chloroplasts that give plant leaves their green color.
Another variety of plastids, chromoplasts, are responsible for yellow, red or orange coloration.
Colorless plastids in the cell act as a storehouse of nutrients. Leukoplasts contain fats, starch, proteins and enzymes. When the plant needs additional energy, starch is broken down into monomers - glucose.
Leukoplasts under certain conditions (under the influence of sunlight or with the addition of chemicals) can turn into chloroplasts, chloroplasts are converted into chromoplasts when chlorophyll is destroyed, and the coloring pigments of chromoplasts - carotene, anthocyanin or xanthophyll - begin to predominate in color. This transformation is noticeable in autumn, when leaves and many fruits change color due to the destruction of chlorophyll and the manifestation of chromoplast pigments.
Functions
As mentioned above, plastids can be different, and their functions in a plant cell depend onvarieties.
Leucoplasts serve mainly to store nutrients and maintain the life of the plant due to the ability to store and synthesize proteins, lipids, enzymes.
Chloroplasts play a key role in the process of photosynthesis. With the participation of the chlorophyll pigment concentrated in plastids, carbon dioxide and water molecules are converted into glucose and oxygen molecules.
Chromoplasts, due to their bright coloration, attract insects for pollination of plants. The study of the functions of these plastids is still ongoing.
