Deficiency Symptoms of Essential Elements: Plants require various mineral elements for their normal growth, development and metabolism. They fulfil their mineral requirement from the soil. That means all the essential elements must be present in the soil where a plant grows. If a particular element or a group of elements become limited in the soil, plant growth would be retarded.  Each element in plants plays one or more specific structural or functional roles, and plants exhibit certain morphological changes when that element is limited. These externally visible morphological changes, which result from a lack of essential minerals, are called hunger signs or deficiency symptoms of essential elements.

Definition of Critical Concentration

The concentration of an essential element below which plant growth is retarded is known as the critical concentration. When the element’s concentration falls below the critical level, it is considered deficient. These externally visible morphological changes, which result from a lack of essential minerals, are called deficiency symptoms. They are also called hunger signs. The symptoms of deficiency vary from element to element, and they disappear when the plant receives the deficient mineral nutrient. It is, however, possible that if the plant is deprived for long enough, it will eventually die.

Common Deficiency Symptoms

The most common deficiency symptoms observed in plants include:

1. Chlorosis: It is the loss of chlorophyll leading to yellowing in leaves. It is caused by the deficiency of elements N, K, Mg, S, Fe, Mn, Zn and Mo.
2. Necrosis: It refers to the death of tissue, particularly leaf tissue. It is caused by a deficiency of Ca, Mg, Cu, and K.
3. Inhibition of Cell Division: It is caused by low levels of N, K, S and Mo.
4. Late Flowering: Some elements like N, S, and Mo delay flowering if their concentration in plants is low.

The mobility of the specific element can also influence which plant parts exhibit the deficiency. A deficiency normally manifests in the older tissues first for elements that are actively mobilised within the plants and exported to young developing tissues. For example, N, K and Mg deficiency symptoms are visible first in the senescent (older) leaves. In the older leaves, biomolecules containing those elements are broken down, thereby making these elements available for mobilising to younger leaves.

On the other hand, when the elements are immobile and are not transported out of the mature organs, the deficiency symptoms tend to appear first in the young tissues. Calcium, for instance, is not easily released since it is part of the structural components of the cell.

Mineral Elements	Deficiency Symptoms
Nitrogen	It causes yellowing of leaf (chlorosis), stunting of plants, dormancy of lateral buds and seeds, late flowering, purple colouration in shoot axis due to accumulation of anthocyanin, smaller cells and inhibition or slow division.
Sulphur	Chlorosis of younger leaves, stunted growth and anthocyanin accumulation, leaf curls, reduced nodulations in legumes, less juice content in citrus plants, smaller chlorotic veins in tea leaves, root and stem becomes woody due to development of sclerenchyma.
Phosphorus	Stunted growth in young plants and dark green colouration of the leaves, necrotic spots, delay in seed germination, purple or red spots on a leaf of anthocyanin, premature fall of leaf and buds, delayed flowering.
Silicon	Water lodging and fungal infection.
Boron	Black necrosis of young leaf and terminal buds, death of root and shoot tips, abscission of flowers, the small size of fruits, development of rosette condition. There is a shift from the glycolysis pathway to the HMP shunt pathway.
Iron	It causes intervenous chlorosis, necrosis, and reduced growth, it blocks the electron transport chain and thus hampers photosynthesis and cellular respiration.
Zinc	Reduction in intermodal growth causes a rosette habit of growth, interveinal, white bud, stunted growth, chlorosis, inhibits seed germination and inhibits elongation of root and shoot, causing Khaira disease of rice.
Copper	Production of dark green leaves, necrotic spots on the tip of a young leaf.
Nickel	Leaf tip necrosis
Molybdenum	It causes nitrogen deficiency, causes general chlorosis between veins and necrosis of older leaves, causes whiptail disease in cauliflower, as well as the loosening of inflorescence in cauliflower.
Potassium	Moltted or marginal chlorosis causes scorched leaf tips, shorter internodes, loss of apical dominance, loss of cambial activity. It stops the carbohydrate metabolism, storage of carbohydrates in potato and beet is inhibited.
Calcium	Necrosis of young meristematic regions, general chlorosis and downward hooking of young leaf causes blackheart disease of celery. It also causes irregular cell divisions(mitosis) and the death of meristem.
Magnesium	Chlorosis of leaf veins, necrotic or purple coloured spot on older leaf, premature leaf abscission. It blocks the Krebs’ cycle as well as glycolysis.
Chlorine	Wilting of leaf tips, leaf chlorosis, necrosis, stunted root growth and reduced fruiting.
Manganese	Intervenous chlorosis and development of small necrotic spots, disorganisation of the thylakoid membrane, causes marsh spot of a pea. It affects chlorophyll formation.
Sodium	Chlorosis and necrosis
Zinc	Reduction in internodal growth and as a result plants show a rosette habit of growth. The leaves may also be small and distorted. In some plants, the older leaves become intravenously chlorotic. Causes Khaira disease of rice.

Toxicity of Micronutrients

Micronutrients are always required in low amounts. Their moderate decrease in the soil causes deficiency symptoms. A moderate increase in their concentrations, however, can cause toxicity, as each element has a narrow range of optimum concentrations.

Mineral ion concentrations in tissues that reduce the dry weight by more than 10% are considered toxic. There may be toxic effects from direct excesses of micronutrients or interference with the absorption and functioning of other nutrients. For example, the prominent symptom of manganese (Mn) toxicity is the appearance of brown spots surrounded by chlorotic veins.

Excess of Mn causes:

a. Reduction in the uptake of Mg and Fe.
b. Prevention of binding of Mg with enzymes.
c. Inhibition of Ca translocation to shoot apex.

Therefore excess manganese may induce deficiencies of iron. magnesium, and calcium. Thus. The toxicity effects of Mn are due to combined deficiency symptoms of Mg, Fe and Ca.

Summary

Plants require mineral elements for their proper growth and development. There are 17 essential elements out of 107 elements present. If the mineral element required is more than 10 millimoles per kg, it is considered a macronutrient. If the mineral element required is less than 10 millimoles per kg, it is considered a micronutrient. If the concentration of micronutrients increases, it causes toxicity in the plant and competes with other macronutrients for its uptake. The most common deficiency symptoms are chlorosis, necrosis, inhibition of cell division, late flowering, and manganese toxicity in the plant.

Frequently Asked Questions (FAQs)

Q.1. What are the deficiency symptoms of hydrogen in plants?
Ans: The hydrogen deficiency causes chlorosis, foliage colour changes, overall plant stunting and sometimes necrosis in plants.

Q.2. What are the effects of manganese toxicity in plants?
Ans: The symptoms of manganese toxicity include necrotic spots surrounded by chlorotic veins.

Q.3. What are the three primary macronutrients for plants?
Ans: The primary macronutrients of plants are Nitrogen (N), Phosphorus (P) and Potassium (K).

Q.4. What happens if the concentration of micronutrients is increased?
Ans: It acts as a toxin in plants when the concentration of micronutrients increases.

Q.5. What are the deficiency symptoms of nitrogen in plants?
Ans: The nitrogen deficiency causes yellowing of leaf (chlorosis), stunting of plants, dormancy of lateral buds, late flowering.

  

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