Plants acquire their raw materials from the environment. They get carbon dioxide and oxygen from the atmosphere which is the source of carbon and oxygen. They obtain the remaining nutrition from minerals. These minerals are absorbed along with the water from the soil.
Uptake of Mineral ions
There are two ways of absorption or uptake of mineral nutrients from the soil. They are active and passive absorption. Root is the organ of the plant which absorbs water and minerals. Minerals are present as charged particles (ions) in the soil. Passive absorption of minerals occurs along with the absorption of water through root hairs, but this process is very rare.
Most of the minerals are actively absorbed by the roots by specific carrier proteins present in the membranes of root hair cells. These proteins actively pump ions from the soil into the cytoplasm of the epidermal cells. From the epidermal cells, the ions move through the cortical cells and reach the cells of endodermis. Here transport proteins of endodermal cells act as traffic police as it checks the quantity and types of solutes that reach the xylem. Since the endodermis consists of suberin coating and only the passage cells allows the water and solute to pass through, it actively transports mineral ions to move in one direction only. Active absorption of minerals ions is being a complex process, so it needs energy in the form of ATP.
Active Absorption of mineral ions
Translocation of Mineral Ions
Once the minerals ions are absorbed by the roots through active or passive way, they were transported by the stem to the other parts of the plants. Movement of ions occurs from the region of source to the region of sink. In plants, the growing apices, young leaves, developing flowers, fruits and seeds are the chief areas of sink.
Following are some of the areas of translocation in plants
- Mineral ions accumulated in the older drying leaves are transferred to younger leaves.
- Remobilization of mineral ions occurs from the older senescing parts to the young meristematic regions.
- Mineral ions are not only carried in inorganic form they are also carried in organic form, eg., an analysis of xylem exudates shows the presence of nitrogen as both inorganic ions and also in the organic form as amino acids and related compounds.