Mineral Nutrition

Mineral Nutrition

Essential mineral elements:

  • Essential mineral elements are nutrients required by plants for their growth and development. 
  • These elements are crucial for various physiological processes and cannot be substituted by other elements. 
  • Major essential mineral elements include nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, zinc, copper, molybdenum, boron, and chlorine. 

 

Soil as a Reservoir of Essential Elements:

 

  • Source of Nutrients:

- Nutrients essential for plant growth and development are primarily obtained by roots from the soil.

- Weathering and breakdown of rocks enrich the soil with dissolved ions and inorganic salts, making them available for plant uptake. 

  • Mineral Nutrition:

- The role of soil-derived nutrients in plant nutrition is known as mineral nutrition.

- Soil contains various substances essential for plant growth, including minerals, nitrogen-fixing bacteria, and other microbes. 

  • Functions of Soil:

- Soil not only provides minerals but also supports vital functions such as water retention, aeration for roots, and stabilization of plants.

- It acts as a matrix that anchors and supports plant growth, contributing to overall plant stability. 

  • Importance of Soil Fertility:

- Deficiency of essential minerals can significantly impact crop yield, emphasizing the importance of soil fertility.

- To address deficiencies, fertilizers containing both macro and micronutrients are applied as needed. 

  • Fertilizer Components:

- Fertilizers contain both macro-nutrients (e.g., N, P, K, S) and micronutrients (e.g., Cu, Zn, Fe, Mn), supplied to plants based on specific requirements. 

 

Diverse Mineral Uptake by Plants:

 

  • Plants have the ability to absorb a wide range of minerals from the soil through their roots. 
  • Over sixty elements out of the 105 discovered are found in various plant species.
  • Certain plants, such as those accumulating selenium or gold, demonstrate the diverse range of minerals that plants can uptake. 
  • Some plants growing in unique environments, like near nuclear test sites, can even absorb radioactive elements like strontium.

 

Mechanism of Element Absorption in Plants

 

  • Study Approach:

- Research on element absorption in plants has mainly focused on isolated cells, tissues, or organs.

- These studies have revealed a two-phase process of absorption. 

  • Phases of Absorption:

- First Phase: Initial rapid uptake of ions occurs in the apoplast, the outer space of cells, through passive movement.

- Second Phase: Ions are slowly taken into the symplast, the inner space of cells, through active processes. 

  • Passive Movement:

- Ions enter the apoplast through ion-channels, trans-membrane proteins acting as selective pores.

- This process is passive and does not require metabolic energy. 

  • Active Transport:

- Entry or exit of ions into and from the symplast requires the expenditure of metabolic energy.

- This process is active and involves energy consumption by the plant. 

  • Ion Movement:

- Movement of ions is termed as flux, with inward movement into cells referred to as influx, and outward movement as efflux.

 

Translocation of Solutes in Plants

 

  • Transport through Xylem:

- Mineral salts are transported through the xylem along with the ascending stream of water.

- This movement is facilitated by transpirational pull, where water is pulled up through the plant. 

  • Presence in Xylem Sap:

- Analysis of xylem sap confirms the presence of mineral salts, indicating their translocation through the xylem. 

  • Radioisotope Studies:

- Use of radioisotopes of mineral elements further supports the evidence of their transportation through the xylem.

 

Hydroponics-  A method to study the mineral requirements of plants 

 

 

  • In 1860, Julius von Sachs, a prominent German botanist, pioneered the technique of growing plants in a defined nutrient solution without soil, known as hydroponics. 
  • Hydroponics revolutionized plant cultivation by allowing precise control over nutrient intake and eliminating soil dependence. It helps to understand mineral requirements of plants. 
  • Through experiments involving the immersion of plant roots in nutrient solutions with varied element concentrations, essential elements were identified and deficiency symptoms discovered. 
  • These experiments formed the basis for understanding plant nutrient requirements and optimizing hydroponic nutrient solutions. 
  • Hydroponics has been successfully employed for commercial production of vegetables such as tomatoes, seedless cucumbers, and lettuce. 
  • Its controlled environment and precise nutrient delivery system result in high-quality, high-yield crops. 
  • Adequate aeration of nutrient solutions is crucial for optimal plant growth in hydroponics. 
  • Poorly aerated solutions can lead to oxygen deprivation in plant roots, causing root rot, nutrient uptake issues, and ultimately stunted growth or plant death. 

 

 

  • Hydroponic plant production involves growing plants without soil, using a nutrient-rich solution to provide essential minerals directly to the roots. Here's how it works: 

- Setup: Plants are typically grown in tubes or troughs placed on a slight incline. A pump circulates a nutrient solution from a reservoir to the elevated end of the tube. 

- Nutrient Solution: The nutrient solution contains all the essential minerals needed for plant growth and development. It is carefully balanced to provide optimal nutrition. 

- Flow of Solution: The solution flows down the tube, bathing the roots of the plants as it moves. This continuous flow ensures that the roots are adequately supplied with nutrients and oxygen. 

- Return to Reservoir: After reaching the end of the tube, the solution returns to the reservoir due to gravity. This closed-loop system ensures efficient use of water and nutrients. 

- Aeration: It's crucial to aerate the nutrient solution to ensure adequate oxygenation for the roots. Aerated nutrient solution promotes healthy root growth and prevents root rot.

 

Techniques for Detecting Minerals:

 

  • Advanced techniques are available to detect minerals in plants, even at very low concentrations (10-8 g/mL). 
  • These techniques enable researchers to analyze the mineral composition of plants and identify both essential and non-essential elements. 
  • The decision on whether a mineral is essential for plants involves rigorous experimentation and analysis. 
  • Researchers conduct studies where individual minerals are added or withheld from plant growth mediums to observe their effects.

 

Criteria for essentiality

 

1.    Absolute Necessity for Normal Growth and Reproduction:

- Essential elements must be vital for supporting the normal growth and reproductive processes of plants.

- In the absence of these elements, plants are unable to complete their life cycle or produce seeds. 

2.    Specific and Irreplaceable Requirement:

- The requirement of essential elements must be specific to that element and cannot be substituted by another element.

- Deficiency of any essential element cannot be compensated for by supplying a different element. 

3.    Direct Involvement in Plant Metabolism:

- Essential elements must directly participate in the metabolic processes of plants.

- They play crucial roles in various biochemical reactions necessary for plant growth, development, and overall metabolism. 

Implications of the Criteria:

  • Based on these criteria, only a select few elements have been identified as absolutely essential for plant growth and metabolism. 
  • These essential elements are further categorized into two broad groups based on their quantitative requirements:

- Macronutrients: Essential elements required by plants in relatively large quantities for normal growth and development. Examples include nitrogen, phosphorus, potassium, calcium, magnesium, and sulphur.

- Micronutrients: Essential elements needed by plants in smaller quantities but still crucial for various metabolic processes. Examples include iron, manganese, zinc, copper, molybdenum, boron, and chlorine.

 

 

Macro-nutrients

  • Macronutrients are essential elements found in plant tissues in relatively large amounts, exceeding 10 mmole per kilogram of dry matter. 
  • These nutrients are vital for sustaining plant growth and development. 
  • Macronutrients include:

- Carbon,

- Hydrogen,

- Oxygen,

- Nitrogen,

- Phosphorus,

- Sulphur,

- Potassium,

- Calcium,

-Magnesium 

  • Carbon, hydrogen, and oxygen are primarily obtained from carbon dioxide (CO2) and water (H2O) through photosynthesis. 
  • The remaining macronutrients are absorbed from the soil as mineral nutrition, facilitated by plant roots.

Roles of Macronutrients:

Carbon (C):

- Obtained from carbon dioxide (CO2) during photosynthesis.

- Serves as the primary building block for organic molecules, including carbohydrates, proteins, lipids, and nucleic acids.

- Essential for energy production, structural integrity, and overall plant metabolism. 

Hydrogen (H):

- Derived from water (H2O) during photosynthesis and other metabolic processes.

- Contributes to the structure of organic molecules, including carbohydrates, proteins, and lipids.

- Essential for maintaining pH balance, facilitating biochemical reactions, and supporting plant growth and development.

 Oxygen (O):

- Derived from water (H2O) and carbon dioxide (CO2) during photosynthesis.

- Integral component of organic molecules, including carbohydrates, proteins, lipids, and nucleic acids.

- Essential for cellular respiration, energy production, and metabolic processes throughout the plant.

Nitrogen (N):

- Essential in the greatest quantity among all nutrient elements.

Absorbed primarily as NO3- (nitrate), with some uptake as NO2- (nitrite) or NH4+ (ammonium).

- Required by all parts of the plant, especially meristematic tissues and metabolically active cells.

- Major constituent of proteins, nucleic acids, vitamins, and hormones, essential for growth and development. 

Phosphorus (P):

- Absorbed as phosphate ions (H2PO4- or HPO42-) from the soil.

- Essential for cell membranes, certain proteins, nucleic acids, and nucleotides.

- Required for phosphorylation reactions, vital for energy transfer and cellular metabolism. 

Potassium (K):

- Absorbed as potassium ions (K+) by various plant tissues, including meristems, leaves, and roots.

- Maintains anion-cation balance in cells, crucial for osmoregulation and turgor pressure.

- Involved in protein synthesis, regulation of stomatal opening and closing, enzyme activation, and cell turgidity. 

Calcium (Ca):

- Absorbed as calcium ions (Ca2+) from the soil, essential for meristematic and differentiating tissues.

- Utilized in cell wall synthesis, particularly as calcium pectate in the middle lamella, and during mitotic spindle formation.

- Essential for normal cell membrane functioning, enzyme activation, and regulation of metabolic activities. 

Magnesium (Mg):

- Absorbed as divalent Mg2+ ions by plants, crucial for enzyme activation in respiration and photosynthesis.

- Required for DNA and RNA synthesis, as well as maintaining ribosome structure.

- Constituent of chlorophyll's ring structure, essential for photosynthesis and overall plant growth. 

Sulphur (S):

- Obtained as sulphate ions (SO42-) from the soil, incorporated into amino acids like cysteine and methionine.

- Main constituent of coenzymes, vitamins (e.g., thiamine, biotin, Coenzyme A), and ferredoxin.

- Essential for protein synthesis, coenzyme activation, and various metabolic processes in plants. 

Micro-nutrients

  • Required in very small amounts, less than 10 mmole per kilogram of dry matter. 
  • Include iron, manganese, copper, molybdenum, zinc, boron, chlorine, and nickel. 
  • Necessary for higher plants despite being required in small quantities. 
  • Examples include sodium, silicon, cobalt, and selenium. 
  • Functional Categories of Essential Elements

1. Components of Biomolecules and Structural Elements of Cells:

- Examples: Carbon, hydrogen, oxygen, and nitrogen.

- Found in essential organic compounds such as carbohydrates, proteins, lipids, and nucleic acids. 

2. Components of Energy-Related Chemical Compounds:

- Examples: Magnesium in chlorophyll, phosphorus in ATP (adenosine triphosphate).

- Crucial for energy transfer and storage in plants. 

3. Enzyme Activators or Inhibitors:

- Examples: Magnesium (Mg2+) as an activator for ribulose bisphosphate carboxylase-oxygenase (RuBisCO) in photosynthesis.

- Other examples include zinc (Zn2+) activating alcohol dehydrogenase and molybdenum (Mo) activating nitrogenase during nitrogen metabolism. 

4. Osmotic Regulation and Stomatal Function:

- Elements that alter the osmotic potential of cells and regulate stomatal opening and closing.

- Example: Potassium (K+) plays a crucial role in regulating stomatal movements and influencing the osmotic potential of cells. 

Roles of Essential Micronutrients:

Iron (Fe):

- Absorbed as ferric ions (Fe3+) by plants, required in larger quantities compared to other micronutrients.

- Essential constituent of proteins involved in electron transfer, such as ferredoxin and cytochromes.

- Crucial for chlorophyll formation and activation of catalase enzyme, aiding in oxidative stress response. 

Manganese (Mn):

- Absorbed as manganous ions (Mn2+), essential for activating enzymes in photosynthesis, respiration, and nitrogen metabolism.

- Key role in splitting water molecules during photosynthesis, liberating oxygen and facilitating electron transport. 

Zinc (Zn):

- Plants absorb zinc as Zn2+ ions, necessary for activating various enzymes, particularly carboxylases involved in carbon fixation.

- Essential for auxin synthesis, regulating plant growth and development. 

Copper (Cu):

- Absorbed as cupric ions (Cu2+), essential for overall metabolic processes in plants.

- Participates in redox reactions with certain enzymes, aiding in electron transfer and metabolic regulation.

Boron (B):

- Absorbed as borate ions (BO33- or BO47-), required for various physiological processes including membrane functioning, pollen germination, and cell elongation.

- Facilitates uptake and utilization of calcium ions (Ca2+), crucial for cell differentiation and carbohydrate translocation. 

Molybdenum (Mo):

- Obtained by plants as molybdate ions (MoO22+), essential component of enzymes like nitrogenase and nitrate reductase involved in nitrogen metabolism.

- Plays a critical role in nitrogen fixation and assimilation processes.

Chlorine (Cl):

- Absorbed as chloride anions (Cl-), along with sodium (Na+) and potassium (K+), helps in maintaining solute concentration and anion-cation balance in cells.

- Essential for water-splitting reaction during photosynthesis, leading to oxygen evolution and overall energy production. 

Toxicity of Micronutrients

1. Narrow Optimum Range:

- Micronutrients are required in low amounts, and even a moderate decrease causes deficiency symptoms, while a moderate increase leads to toxicity.

- There exists a narrow concentration range where micronutrients are optimal for plant growth and development. 

2. Toxicity Threshold:

- Any mineral ion concentration in tissues that reduces dry weight by about 10% is considered toxic.

- Critical concentrations for toxicity vary widely among different micronutrients. 

3. Difficulty in Identifying Toxicity Symptoms:

- Toxicity symptoms are challenging to identify and may vary for different plants.

- Excess of one element may inhibit the uptake of another element, further complicating toxicity symptoms. 

4. Interactions and Competition:

- Excessive manganese, for example, competes with iron, magnesium, and calcium for uptake and binding with enzymes.

- Manganese toxicity symptoms include brown spots surrounded by chlorotic veins, resembling deficiency symptoms of other essential elements. 

5. Importance in Agriculture and Gardening:

- Understanding interactions between micronutrients is crucial for farmers and gardeners to optimize plant nutrition and prevent toxicity.

- Farmers can adjust nutrient application rates to avoid imbalances and ensure optimal plant growth and yield.

- Gardeners can monitor plant health and adjust fertilizer formulations accordingly to prevent nutrient imbalances and toxicity.

- Awareness of nutrient interactions is also valuable for kitchen gardeners to maintain healthy and productive plants.

 

Nutrients Deficiency

 

  • Critical concentration refers to the threshold below which plant growth is retarded due to limited supply of an essential element. 
  • When an essential element falls below the critical concentration, it is termed deficient, impacting plant growth and development. 
  • Morphological changes in plants indicate deficiencies and are termed deficiency symptoms. 
  • These symptoms vary depending on the specific roles of each element in plant physiology. 
  • Deficiency symptoms disappear upon providing the deficient element but can lead to plant death if deprivation continues. 
  • Symptoms appear first in tissues where elements are immobile or not transported out of mature organs. 
  • Mobile elements tend to show deficiency symptoms in older tissues, while immobile elements affect young tissues first. 
  • Understanding mineral nutrition deficiencies is crucial for optimizing crop production and horticultural practices. 
  • Types of Deficiency Symptoms:

- Chlorosis: Loss of chlorophyll leading to yellowing of leaves, caused by deficiencies in N, K, Mg, S, Fe, Mn, Zn, and Mo.

 

- Necrosis: Death of tissue, particularly leaf tissue, due to deficiencies in Ca, Mg, Cu, K.

 

 

- Inhibition of cell division: Caused by deficiencies in N, K, S, Mo, leading to stunted growth.

- Delayed flowering: Caused by deficiencies in N, S, Mo, affecting reproductive development.

 

 

 

  • Complexity of Symptoms:

- Deficiency of any element can cause multiple symptoms, and the same symptoms may result from deficiencies in different elements.

- Identifying the deficient element requires careful observation of symptoms across various plant parts and comparison with standard tables.

- Different plant species may respond differently to the deficiency of the same element.