Options:
(a) (i), (ii) and (iii)
(b) (i) and (ii)
(c) (iii) and (iv)
(d) (ii), (iii) and (iv)
Answer:(c) (iii) and (iv)
(c) Manganese competes with iron and magnesium for uptake, and with magnesium for binding with enzymes. Manganese also inhibits calcium translocation in shoot apex.
•Any mineral ion concentration in tissues
that reduces the dry weight of tissues by about 10 per cent is considered
toxic.
•Many a times, excess of an
element may inhibit the uptake of another element.
•For example, the
prominent symptom of manganese toxicity is the appearance of brown
spots surrounded by chlorotic veins.
•It is important to know that
manganese competes with iron and magnesium for uptake and with
magnesium for binding with enzymes
• Manganese also inhibit calcium
translocation in 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
•Micronutrients or trace elements, are needed in very small amounts
(less than 10 mmole Kg^ –1 of dry matter). These include iron, manganese,
copper, molybdenum, zinc, boron, chlorine and nickel.
•Manganese: It is absorbed in the form of manganous ions (Mn2+). It
activates many enzymes involved in photosynthesis, respiration and
nitrogen metabolism
•The best defined function of manganese is in the
splitting of water to liberate oxygen during photosynthesis.
