Biology · Ch 7 — Plant Growth and Mineral Nutrition
Symptoms of Mineral Deficiency
Symptoms of Mineral Deficiency
Symptoms of Mineral deficiency in plants : Any visible deviation of a plant from its normal structure or function is called a symptom, or 'hunger sign', of mineral deficiency. The concentration of an essential element below which plant growth is retarded is called its critical concentration; an element is said to be deficient once its level in the plant falls below this critical concentration.
Where in the plant a deficiency symptom first appears depends on how mobile that element is within the plant. Elements that are relatively immobile -- such as sulphur and calcium -- cannot be withdrawn from older tissue and resupplied to young tissue, so their deficiency symptoms appear first in the young, actively growing tissues. Elements that are actively mobilised and exported from older tissue to young developing tissue -- such as nitrogen, magnesium and potassium -- instead show their deficiency symptoms first in the older, senescent leaves, since it is the older tissue that gets stripped of the element to support new growth.
Some important deficiency symptoms seen in plants are:
- Stunting : The growth is retarded; the stem appears condensed and short.
- Chlorosis : The loss or non-development of chlorophyll, resulting in yellowing of the leaves.
- Necrosis : Localised death of the tissue of leaves.
- Mottling : The appearance of green and non-green patches on the leaves.
- Abscission : Premature fall of flowers, fruits and leaves.
The roles and characteristic deficiency symptoms of the individual major and trace elements are summarised in Table 7.10.
| Element | Region required | Functions | Deficiency symptom |
|---|---|---|---|
| Nitrogen (NO2-, NO3-, NH4+) | Everywhere, particularly meristematic tissue | Constituent of proteins, nucleic acids, vitamins, hormones, coenzymes, ATP and chlorophyll | Stunted growth, chlorosis |
| Phosphorus (H2PO4-, HPO4^2-) | Younger tissues; obtained from older, metabolically less active cells | Constituent of cell membranes, certain proteins, all nucleic acids and nucleotides; required for all phosphorylation reactions | Poor growth, dull green leaves |
| Potassium (K+) | Meristematic tissues, buds, leaves, root tips | Determines anion-cation balance in cells involved in protein synthesis; forms cell membranes; opens and closes stomata; increases hardness; activates enzymes; maintains cell turgidity | Yellow leaf edges, premature death |
| Calcium (Ca2+) | Meristematic and differentiating tissues; accumulates in older leaves | Involved in selective permeability of cell membranes; activates enzymes for stem/root apex development; forms calcium pectate in the middle lamella | Stunted growth |
| Magnesium (Mg2+) | Leaves; withdrawn from ageing leaves and exported to developing seeds | Activates enzymes in phosphate metabolism; constituent of chlorophyll; maintains ribosome structure | Chlorosis |
| Sulphur (SO4^2-) | Stem and root tips; young leaves; remobilised during senescence | Constituent of certain proteins, vitamins (thiamine, biotin, CoA) and ferredoxin | Chlorosis |
| Iron (Fe3+) | Everywhere; carried along leaf veins | Constituent of ferredoxin and cytochrome; activates catalase needed for chlorophyll synthesis | Chlorosis |
| Manganese (Mn2+, trace) | Leaves and seeds | Activates certain enzymes (carboxylases) | Chlorosis, grey spots on leaves |
| Molybdenum (MoO2^2+/MoO3+, trace) | Everywhere, particularly roots | Activates certain enzymes of nitrogen metabolism | Slight retardation of growth |
| Boron (BO3-/B4O7^2-, trace) | Leaves and seeds | Required for uptake and utilisation of Ca2+, pollen germination, cell differentiation and carbohydrate translocation | Brown-heart disease |
Do you know?
- Constituents of protoplasm and cell walls : C, H, O, N, P and S are important and permanent constituents of the protoplasm and the cell wall.
- Osmotic potential : The osmotic pressure of a cell is the result of the mineral salts and organic compounds dissolved in the cell sap.
- Catalytic functions : Many elements like Fe, Cu, Zn, Mg, Mn, Cl, Mo and B act as catalysts in various enzyme reactions of plant metabolism. …