Molybdenum: It is present in minute quantity 0.00001%. Source: soil, in the form of Molybdale Mo 04- Functions: Role in nitrogen fixation Activator & nitrate reeducate
Deficiency symptoms: Interveinal chlorosis followed by necrosis. Young leaves become twisted. Whip tail disease of crucifers.
6. Boron: 0.002% of dry weight Source: Soil, it is absorbed as borate ions (H2Bo3-)
Functions of Boron: Translocation of sugars involved.DNA synthesis in meristems. Acts as natural inhibitor.
Deficiency Symptoms of Boron: Death of shoot tips. Leaves become thick coppery texture & curling. Flowering is suppressed.Root growth is stunted. In storage organs browning of internal tissue occurs. Heart rot of beet root, water core of turnip, top sickness of tobacco etc.
7. Chlorine: 0.01% of dry weight Source: Soil, as chloride ions Cl- Functions: Stimulates splitting of water molecule during Photosynthesis. Essential for growth of roots and for division of leaf cells.Deficiency symptoms:Leaves become wilted. Leaves may show chlorosis & necrosis.Roots become thick & stunted.
Toxicity of Micronutrients:Requirement of micronutrients is always low but their further decrease in concentration causes deficiency symptoms and their increase causes toxicity.Any mineral ion concentration in tissues that reduces the dry weight by about 10% is consideread toxic. Toxicity levels for any element also very for different plants. Sometimes excess of an element may inhibit the intake of another element. Example: Symptoms of Manganese toxicity is the appearance of brown spots surrounded by chlorotic veins. Manganese Competes with Iron and Magnesium for uptake & with Magnesium for binding with enzymes. Manganese also inhibits Calcium translocation in shoot apex. Therefore excess of Manganese may induce deficiencies if Iron Fe, Magnesium and Calcium. Thus what appear as symptoms of Manganese toxicity may be the deficiency symptoms of Iron, Magnesium and Calcium.

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