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Deficiency symptoms of essential elements and toxicity
 

iacst-2022

Introduction:

  • Plant growth development and metabolism are dependent on various essential elements.
  • The major source of obtaining those elements is the soil.
  • If the soil lacks any of the essential elements it can affect plant growth and many physiological functions.
  • Plants begin to exhibit certain morphological changes due to deficiency of a certain essential element.
  • Toxicity is the excessive accumulation of substances that induces harmful effects.
  • These nutrients are required in a very limited amount and have a narrow range of operation.
  • Slight excess above the optimal amount, therefore, becomes toxic for the plants.

Topics covered-

  • Deficiency symptoms of essential elements
  • Differentiate between mobile and immobile elements
  • Toxicity of micronutrients

Deficiency symptoms of essential elements
 

Introduction:

  • The concentration of the essential elements below which plant growth get retarded is termed as critical concentration.
  • This means there is a lack of certain essential elements in the soil.
  • Every element has specific roles in the structural or functional aspect.

Detailed explanation:

  • The changes in morphology which are very clearly visible in the plant body due to lack of certain essential elements are known as the deficiency symptoms.
  • The continuation of element deprivation can lead to plant death as well.
  • These symptoms change depending upon the essential element lacking.
  • The deficiency symptoms can be cured by supplementing the plant with the particular essential element that caused the symptoms.
  • The symptoms also depend on how elements are transported within the plant body.
  • The elements which are actively mobilised or transported tend to move towards growing or young regions resulting in deficiency symptoms at the older tissues.
  • The deficiency symptoms of elements nitrogen, potassium and magnesium are first seen in the older or senescent leaves.
  • The biomolecules which are constituted of N, K and Mg are broken down and are readily mobilized to the young regions or young leaves of the plant.
  • When younger plant parts show deficiency symptoms the reason is that some elements are not easily mobile or rather immobile.
  • Calcium is a structural component in the mature regions that are not easily released causing symptoms in younger regions.
  • Deficiency symptoms might occur due to deficiency or lack of one or more than one element.
  • Deficiency symptoms intensity might vary greatly from one plant to another for the same set of elements.
  • Excessive concentration of elements can also be toxic or harmful to plants.
  • The deficiency of any element can cause multiple symptoms and the same symptoms may be caused by the deficiency of one of several different elements.
  • Hence, to identify the deficient element, one has to study all the symptoms developed in all the various parts of the plant and compare them with the available standard tables.
  • We must also be aware that different plants also respond differently to the deficiency of the same element.

Common deficiency symptoms -

  • The deficiency symptoms observed most commonly in plants are chlorosis, necrosis, stunted plant growth, premature fall of leaves and buds, and inhibition of cell division.

Chlorosis -

  • The yellowing of leaves is due to the absence or loss of chlorophyll. It is caused due to deficiency of elements like N, K, Mg, S, Fe, Mn, Zn, and Mo.

Necrosis -

  • This is also referred to as tissue death, specifically leaf tissue and is caused due to the deficiency of elements like Ca, Mg, Cu, K.

Inhibition of cell division -

  • Cell division inhibition happens due to the lack or loss of elements like N, K, S, Mo.

Delay in flowering -

  • Delay in flowering is caused due to deficiency of the elements N, S, Mo.

Differentiate between mobile and immobile elements
 

Introduction:

  • The parts of the plants that show the deficiency symptoms also depend on the mobility of the element in the plant.
  • The essential elements can be distinguished into two groups based on their ability to translocate.
  • Elements that are easily translocated to young plant parts in need are called mobile elements, while those elements which are a structural component of the cell and are not released out of the mature organs to young parts are called immobile elements.

Detailed explanation:
 

Mobile elements -

  • These are those elements that are mobile or can be translocated from older tissues to younger ones.
  • The deficiency of mobile elements is found in the older plant parts.
  • For example, the deficiency symptoms of nitrogen, potassium and magnesium are visible first in the senescent leaves.
  • In the older leaves, biomolecules containing these elements are broken down, making these elements available for mobilising to younger leaves.

Immobile elements -

  • These are those elements that are immobile and cannot be translocated towards younger regions from the older ones due to structural complexity or other reasons.
  • These elements do not move around in the plant body and remain active in the regions they first get deposited to.
  • These elements can be a part of structural organs such as cell walls. For example, calcium is a structural component of the cell that functions during cell expansion and hence cannot be released as normally as nitrogen.
  • Due to lack of calcium in the younger shoots or younger regions, these regions exhibits deficiency symptoms.
  • Calcium (Ca) and sulphur (S) are considered as immobile elements.
  • Although, calcium is more immobile as compared to sulphur.

Toxicity of micronutrients
 

Introduction:

  • Micronutrients are those elements that have a narrow range of operation.
  • They are needed by plants in minimal quantities.
  • Toxicity is the harmful effect caused due to the slight excess of these nutrients.

Detailed explanation:

  • The requirement of micronutrients is always in low amounts while their moderate decrease causes the deficiency symptoms and a moderate increase causes toxicity.
  • There is a narrow range of concentration at which the elements are optimum.
  • Just like deficiency symptoms is the reduction or lack of the correct amount of elements. Toxicity is a mild increase of an element.
  • Toxic concentration can be described as the concentration of mineral ions in tissues that reduces the dry weight of tissues by 10 %.
  • Such critical concentrations vary widely among different micronutrients.
  • The toxicity symptoms are difficult to identify as they are not very direct like deficiency symptoms. Toxicity works in a more complex manner.
  • Toxicity levels for any element also vary for different plants.
  • Toxicity can be described as an excess of a particular element that could hinder (inhibit) the uptake or absorption of another essential element.
  • Manganese toxicity can be characterized by the appearance of brown spots accompanied by chlorotic veins.
  • Manganese directly competes with magnesium and iron for uptake and with magnesium for enzyme binding.
  • Manganese toxicity can inhibit calcium translocation to the shoot apex.
  • Therefore, excess of manganese may, in fact, induce deficiencies of iron, magnesium and calcium.
  • Thus, what appears as symptoms of manganese toxicity may actually be the deficiency symptoms of iron, magnesium and calcium.

Frequently Asked Questions: FAQs
 

Q1. What do you mean by critical concentration?
Answer:
The concentration of the essential elements below which plant growth get retarded is termed as critical concentration.

Q2. How deficiency of essential elements can lead to death in plants?
Answer:
The changes in morphology which are very clearly visible in the plant body due to lack of certain essential elements are known as the deficiency symptoms.The continuation of element deprivation can lead to plant death as well.

Q3. How do deficiency symptoms occur in older tissues?
Answer:
The elements which are actively mobilised or transported tend to move towards growing or young regions resulting in deficiency symptoms showing at the older tissues.The deficiency symptoms of elements nitrogen, potassium and magnesium are first seen on the older or senescent leaves.

Q4. Chlorosis symptoms appear due to deficiency of?
Answer:
The yellowing of leaves is due to the absence or loss of chlorophyll. It is caused due to deficiency of elements like N, K, Mg, S, Fe, Mn, Zn, and Mo.

Q5. Describe mobile elements.
Answer:

  • These are those elements that are mobile or can be translocated from older tissues to younger ones.
  • The deficiency of mobile elements is found in the older plant parts.
  • For example, the deficiency symptoms of nitrogen, potassium and magnesium are visible first in the senescent leaves.
  • In the older leaves, biomolecules containing these elements are broken down, making these elements available for mobilising to younger leaves.

Q6. Define immobile elements.
Answer:

  • These are those elements that are immobile and cannot be translocated towards younger regions from the older ones due to structural complexity or other reasons.
  • These elements do not move around in the plant body and remain active in the regions they first get deposited to.
  • These elements can be a part of structural organs such as cell walls. For example, calcium is a structural component of the cell that functions during cell expansion and hence cannot be released as normally as nitrogen.
  • Due to lack of calcium in the younger shoots or younger regions, these regions exhibits deficiency symptoms.
  • Calcium (Ca) and sulphur (S) are considered as immobile elements.
  • Although, calcium is more immobile as compared to sulphur.

Q7. How does micronutrient toxicity happen?
Answer:

  • The requirement of micronutrients is always in low amounts while their moderate decrease causes the deficiency symptoms and a moderate increase causes toxicity.
  • There is a narrow range of concentration at which the elements are optimum.
  • Just like deficiency symptoms is the reduction or lack of the correct amount of elements. Toxicity is a mild increase of an element.
  • Toxic concentration can be described as concentration of mineral ions in tissues that reduces the dry weight of tissues by 10 %.
  • Such critical concentrations vary widely among different micronutrients.

Q8. Explain the effect of Manganese toxicity.
Answer:

  • The toxicity symptoms are difficult to identify as they are not very direct like deficiency symptoms. Toxicity works in a more complex manner.
  • Toxicity levels for any element also vary for different plants.
  • Toxicity can be described as an excess of a particular element that could hinder (inhibit) the uptake or absorption of another essential element.
  • Manganese toxicity can be characterized by the appearance of brown spots accompanied by chlorotic veins.
  • Manganese directly competes with magnesium and iron for uptake and with magnesium for enzyme binding.
  • Manganese toxicity can inhibit calcium translocation to the shoot apex.
  • Therefore, excess of manganese may, in fact, induce deficiencies of iron, magnesium and calcium.
  • Thus, what appears as symptoms of manganese toxicity may actually be the deficiency symptoms of iron, magnesium and calcium.

Q.9. Discuss the common deficiency symptoms in plants.
Answer:
The deficiency symptoms observed most commonly in plants are chlorosis, necrosis, stunted plant growth, premature fall of leaves and buds, and inhibition of cell division.

Chlorosis-

  • The yellowing of leaves is due to the absence or loss of chlorophyll. It is caused due to deficiency of elements like N, K, Mg, S, Fe, Mn, Zn, and Mo.

Necrosis-

  • This is also referred to as tissue death, specifically, leaf tissue and is caused due to the deficiency of elements like Ca, Mg, Cu, K.

Inhibition of cell division-

  • Cell division inhibition happens due to the lack or loss of elements like N, K, S, Mo.

Delay in flowering-

  • Delay in flowering is caused due to deficiency of the elements N, S, Mo.
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