Uptake And Transport Of Mineral Nutrients

Definition Of Mineral Nutrient Transport

In the context of plants, mineral nutrient transport is the means through which essential minerals and/or nutrients are taken up from the soil and mobilized in a plant to fuel physiological activities like photosynthesis, respiration, and growth, among other numerous activities. In a majority of cases, it takes place in roots and is said to be active or passive.

These minerals are conducted in the xylem and phloem in the plant's vascular system. This highly integrated transport system ensures that minerals are translocated in the plant to sustain sufficient healthiness, growth and, reproduction. Understanding these fundamental processes is critical for the advancement of plant nutrition and much more efficient agriculture in general.

Types Of Mineral Nutrients

The types are listed below-

Macronutrients

• Nitrogen: Assists in making amino acids, proteins and chlorophyll.

• Phosphorus: Transport of energy throughout the cell, ATP, DNA, RNA

• Potassium: Enzyme Catalysis, Osmotic/ Ionic Regulation, Stomatal Regulation

• Calcium: Cell Wall structure and integrity

• Magnesium: Chlorophyll, necessary enzyme activation

• Sulfur: Amino acids and vitamins

Micronutrients

• Iron (Fe): Building block of Chlorophyll, electron carrier

• Manganese (Mn): Photosynthesis, nitrogen metabolism, a component of some enzymes.

• Zinc (Zn): For the functioning of enzymes, syntheses of proteins and proper regulation of growth and development.

• Copper (Cu): During photosynthesis and respiration and also as a structural component of lignin in cell walls.

• Molybdän Mo: In the fixation of nitrogen and reduction of nitrates.

• Boron (B): For the formation of cell walls and structural parts.

• Chlorine (Cl): Osmosis and ionic balance are required; it is also essential for photosynthesis.

• Nickel (Ni): Associated with urease activity and the metabolism of nitrogen.

Mechanisms Of Nutrient Uptake

The mechanism is described below-

Passive Transport

Diffusion

• It is the process by which ions of nutrients move from a higher concentration to a lower concentration zone through the cell membrane.

• It is not an energy-dependent process.

Facilitated Diffusion

Classes of transport proteins;

• They participate in the mechanism of transportation of ions of nutrients across the cell membrane.

• It is still determined by the concentration gradient and therefore does not require energy

Active Transport

Role of ATP

• The expenditure of ATP is used to push nutrient ions against their concentration gradient.

• Allowed the cells to develop higher levels of nutrients than are in the soil

Ion Pumps (H+-ATPase)

• Proton pumps use ATP to develop an electrochemical gradient by forcing out of the cell H+ ions.

• That it generates, the gradient and hence drives the movement of other nutrient ions inside the cell down the gradient by co-transport.

Carrier Proteins and Channel Proteins

• Proteins that facilitate the passage by which nutrient ions cross the membrane

• Carrier proteins bind to the nutrient ion and change conformation to take the nutrient ion across the membrane

• The channel proteins are pores in the membrane that only allow specific ions to diffuse down the gradient

Transport Of Nutrients Within The Plant

The transport is described below-

Xylem Transport

Transpiration Pull

This is the process by which water and ions are transported from the roots to the leaves, the primary function of xylemic vessels.

As the water evaporates from the leaf stomata, tension is developed which leads to the production of a negative pressure

Cohesion-Tension Theory

It describes the concept that because of cohesion, the water molecules stick to the xylem vessel walls and make up a single column of water without any discontinuities/ breaks.

This way this continuous column is being dragged upwards by the force being generated because of the transpiration pull.

Role of Tracheary Elements

Specialised xylem cells like tracheids and vessel elements contribute to water and nutrient transport.

Their structure allows easy transport as well as holding of the intact column of water without any failure.

Phloem Transport

Source-Sink Relationship

Movement of nutrients and organic products from 'source' regions, a good example being leaf tissue, into 'sink' regions like root, tubers, and growth regions, into which regions of consumption or storage are spelt out.

Pressure Flow Hypothesis

It describes how the pressure flow of phloem sap rich in nutrients moves from the high-pressure source to the low-pressure sink across the phloem.

This is made possible, firstly, since there are osmotic pressure differentials because of the active loading and unloading of sugars from and into the phloem.

Role of Sieve Elements and Companion Cells

Sieve elements are the main tubes for the transport of nutrients in the phloem and are sap-filled with sieve between their cells; thus the transport can be extremely fast o 7.

There are companion cells that supplement the sieve elements by loading and unloading nutrients and maintaining metabolic functions necessary for transport.

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