Page 3 - LN-CH-12

• In absence of any particular element, plant shows certain morphological changes.
These morphological changes are called deficiency symptoms.

• The parts of plant that show deficiency symptoms depend upon mobility of elements

in the plants. Elements that are actively mobilized (N,Mg,K) show deficiency in older
regions. On the other hand, symptoms appear first in young region if the elements

are relatively immobile (Ca) and not transported out of mature tissues.

• Kinds of deficiency syndrome are as follows-
• Deficiency of any element may cause many symptoms or same symptoms may be
caused by different elements. To identify the deficient elements various symptoms

are compared with standard chart.

Toxicity of micronutrients- in higher doses, micronutrients become toxic. Any

tissue concentration which reduces dry weight of tissue by 10% is called toxic

concentration. Critical toxic concentration is different for different elements.

Mechanism of absorption ofelements

• It takes place in two phases. In first phase, rapid intake of ions occurs in free space or
outer space of the cells, apoplast. In second phase, ions are taken slowly into inner

space, the symplast of the cells.
• Passive movement of ions in apoplast occurs through ion channels and trans•

membrane protein. On the other hand, movement of ions into symplast occurs

by expenditure of energy by active process.

• The movement of ion is called flux. The inward movement is called influx and

outward movement is called efflux .

• Translocation of solutes occur through xylem along with ascending stream of water

Soil as reservoir of essential elements- most of the nutrients required for growth and

development is obtained from soil by roots. These minerals are formed by weathering of

rocks. Soil also harbours nitrogen fixing bacteria and other microbes, holds water and
supplies air to roots. Deficiency of essential elements affects the crop yield. So, fertilisers are

used to supplement these elements.

Metabolism of Nitrogen

• Nitrogen is the most prevalent element in living world along with C, Hand 0. lt is the

main constituent of proteins, nucleic acids, fats, hormones, enzymes etc.