Q. Appearance of brown spots surrounded by chlorotic veins is a toxicity symptom of :

Q. Appearance of brown spots surrounded by chlorotic veins is a toxicity symptom of :

1. Mo
2. Mn
3. Mg
4. Zn

Solution :

Correct option : B Micronutrients are always required in low amounts. Their moderate decrease in the soil causes deficiency symptoms. However, a moderate increase in their concentration can cause toxicity as there is a narrow range of concentration at which the elements are optimum. Any mineral ion concentration in tissues that reduces the dry weight of tissues by about ten percent is considered to be toxic concentration. Appearance of brown spots surrounded by chlorotic veins is a toxicity symptom of Mn. Excess of Mn cause: 1.Reduction in uptake of Mg and Fe. 2. Prevention of binding of Mg with enzymes. 3. Inhibition of Ca translocation to shoot apex.