active and passive nutrient transport system in plants

Submitted to:

Dr. Naveen sir

Dept. of soil science

College of sericulture,

Chintamani.

Submitted by:

Jyothi P

ALC3021, III BSc(agri)

College of sericulture,

Chintamani.

Nutrient transport systemsThere are two methods mainly involved in

transportation of ions in to the plant system.

i. Active transport: when the transport of ions takes place against an electro-chemical gradient.

ii. Passive transport: when the transport of ions takes place along an electro-chemical gradient.

Passive transport system

Absorption of ions in to the inner space is not metabolic i.e. an expenditure of energy by the root cell is not required for this type of absorption and such transport system is known as passive transport system.

It is defined as “transport of ions from the epidermis to the xylem without any consumption of the spontaneous disappearance of non-equilibria driven by a decrease in free enthalpy is known as Passive transport system.”

Thermodynamically Passive transport is the transport down or along electro-chemical gradient.

Passive transport processes can occur in dead or non-respiring tissues and are not sensitive to an inhibitor.

There is no selectivity of ions in this transport processes.

Extracellular spaces exist in the mesophyll cells of leaves where ions are able to diffuse and exchange.

Most of the nutrient ions reach the outer space of the leaves via xylem, from the roots.

Mineral ions in rain, irrigation water and in foliar applications penetrate leaves through the stomata and cuticle to reach the interior of the leaves where they become available for absorption by mesophyll cells.

This is how the ion are taken up through Passive transport system.

Active transport system

Absorption of ions in to the inner space is metabolic i.e. an expenditure of energy by the root cell is required for this type of absorption and such transport system is known as passive transport system.

It is defined as the “process by which ions cross the root from the epidermis to the xylem with the expenditure of metabolic energy against the gradient of their concentration.”

Thermodynamically it is the transport process against an electro-chemical gradient.

Active transport process require the presence of living aerobically respiring cells and can, therefore, mostly be inhibited by metabolic inhibitors.

Active transport process accumulate ions against concentration gradients behind a physiological barrier.

This barrier is assumed to be the permeable to the in-going ions only at expenditure of energy & is impermeable to them as soon as they have been accumulated inside.

Thus the energy involved in active transport is not only required to move ions against concentration gradient, but also forces them through barriers with otherwise would be much less permeable for them, even if the ion movement occurred along the concentration gradient.

Forces involved:

Ions / nutrients in the solutions are subjected to main physical forces

i. Force that arises from the chemical potential gradient.

ii. Force that arises from the electrical potential gradient.

Characteristics of active transport

1. They are specific for given solutes.

Eg: Some cells have a pump specific for certain amino acids but can not transport glucose. Others can pump glucose but not amino acids.

2) It depends on a source of metabolic energy to pump a solute against a gradient of concentration.

eg: Red blood cells obtain the energy required to pump K+ into the cell across the membrane and this needs a highly active glycolytic pathway to provide ATP needed to this transport.

3) The active transport system depends on the conc. of substance being transported.

eg: when glucose is actively transported into a cell, the rate of glucose influx increases with the external conc. of glucose. However, a characteristic plateau is soon reached, so that any further increase in the external glucose produce no increase in the influx

4) Active transport have a specific directionality

K+ is pumped only inward

Na+ is pumped outward.

5) They may be selectively poisoned.

eg: active transport of glucose in the kidney is poisoned by phlorizin.