Many people roughly know what plastids are from school. The botany course says that in plant cells, plastids can be of various shapes, sizes and perform various functions in the cell. This article will remind about the structure of plastids, their types and functions for those who have long graduated from school, and will be useful to everyone who is interested in biology.
Structure
The picture below schematically shows the structure of plastids in the cell. Regardless of its type, it has an external and internal membrane that performs a protective function, the stroma is an analog of the cytoplasm, ribosomes, DNA molecule, enzymes.
In chloroplasts there are special structures - grains. Granes are formed from thylakoids - disc-like structures. Thylakoids are involved in the synthesis of ATP and oxygen.
Starch grains are formed in chloroplasts as a result of photosynthesis.
Leukoplasts are not pigmented. Thylakoids are not present in them, they do not participate in photosynthesis. Most leukoplasts are concentrated in the stem and root of the plant.
Chromoplasts incorporate 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 range from 5-10 microns. The shape is usually oval or round, but can be any other.
Types of Plastids
Plastids can be colorless (leukoplasts), green (chloroplasts), yellow or orange (chromoplasts). It is chloroplasts that give the leaves of plants a green color.
Another variety of plastids, chromoplasts, is responsible for yellow, red or orange color.
Colorless plastids in the cell function as a repository of nutrients. Leukoplasts contain fats, starch, proteins and enzymes. When a plant needs additional energy, starch is broken down into monomers - glucose.
Under certain conditions (under the influence of sunlight or with the addition of chemicals), leukoplasts can turn into chloroplasts, chloroplasts are converted to chromoplasts when chlorophyll is destroyed, and coloring pigments of chromoplasts - carotene, anthocyanin, or xanthophyll - begin to dominate in color. This transformation is noticeable in the fall, when the 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 the plant cell depend on the variety.
Leukoplasts are mainly used for storing nutrients and supporting plant life due to the ability to store and synthesize proteins, lipids, and enzymes.
Chloroplasts play a key role in photosynthesis. With the participation of the chlorophyll pigment concentrated in plastids, the conversion of carbon dioxide and water molecules into glucose and oxygen molecules takes place.
Due to their bright color, chromoplasts attract insects for pollination of plants. Investigation of the functions of these plastids is still ongoing.