Translocation of Nutrient and Elements in plants

Reservoir of nutrient or element for plants - Soil

Majority of the nutrients that are essential for the growth and development of plants  are available in soil and taken by the root to make available  for the plants. The mineral or nutrient are formed inside the soil by the 

weathering and breakdown of rocks.

Since the nutrients are derived from the rock minerals, their role in plant nutrition is referred to as mineral nutrition.

Soil  supplies minerals for plants and also provides spaces  for the nitrogen-fixing bacteria, other microbes. Soil also holds water, supplies air to the roots and acts as a matrix that stabilises the plant.

Both macronutrients  and micronutrients  form components of fertilisers and are supplied when there is deficiency of nutrients.

How to absorb nutrient or elements in Plants

The process of absorption may take place in two ways.  First  The rapid uptake of ions into the free space or outer space of cells by means of the apoplast. It  is a passive method. Second The uptake of  the ions into the ‘inner space  by means of the symplast .

The passive movement of ions into the apoplast takes place through ion-channels and the  transmembrane proteins that function as selective pores in an apoplastic condition.

On the other hand, the entry or exit of ions by the symplast requires the expenditure of metabolic energy.

The movement of ions is usually called the inward movement into the cells is influx and the outward movement is called efflux.

Translocation of Nutrient in Plant

Nutrients  are translocated through xylem along with the ascending stream of water, which is pulled up through the plant by transpirational pull.

Analysis of xylem sap shows the presence of mineral salts in it.

Use of radioisotopes of mineral elements also substantiate the view that they are transported through the xylem.

To facilitate the transport of ions from soils to root, Some carrier proteins are found  in the membranes of root hair cells that actively transport the ions from the soil into the cytoplasm of the epidermal cells.

Carrier proteins of endodermal cells are selective  for the quantity and types of ions or minerals  that reach the xylem. Cell membrane of root hairs allows only some minerals or ions  but not others. 

As the ions have reached xylem through active or passive uptake then their transportation  upto  the stem and to  all parts of the plant takes place  through the transpiration stream.