Question

Which one of the following symptoms is not due to manganese toxicity in plants?
A. Calcium translocation in shoot apex is inhibited.
B. Deficiency in both iron and nitrogen is induced.
C. Appearance of brown spot surrounded by chlorotic veins.
D. None of the above

Answer 1

Hint: Effects of manganese can be seen in plants. The lack of the element is generally based on the alkalinity of soil and inadequate depleted soil. Its deficiency symptoms look like those of iron deficiency.

Complete answer: One of the three elements of essential micronutrients is manganese, while magnesium is one of the essential macronutrients required to properly complete the life cycle of a plant and its physiological activity. In contrast to its role in plant growth and metabolism, excess manganese, while being an essential nutrient, causes toxic effects on plants. As a consequence, its toxicity results in chlorosis in young leaves, necrotic dark spots on mature leaves, and crinkled leaves, ultimately inhibiting the growth of plants. In plants, manganese (Mn) toxicity is also not an obviously identifiable disease. Symptoms of manganese toxicity differ widely among plant different species. The presence of a brown spot surrounded by chlorotic veins is the main symptom of manganese toxicity. It is important to note that manganese competes for absorption with iron and magnesium and with magnesium for enzyme binding. In the shoot apex, manganese also inhibits calcium translocation. Therefore, in fact, excess manganese can induce iron, magnesium and calcium deficiencies. Chlorosis (pale or yellow colour), most extreme on younger leaves due to induced iron deficiency, is also often caused by manganese toxicity. Hence, the correct answer is option B.

Note: Manganese deficiency affects the plant photosynthetic processes because, much like magnesium, molybdenum and zinc, it is an important plant nutrient. Manganese deficiency is easy to cure and homeowners have several options when treating these symptoms. The first is to adjust the soil pH. Two materials commonly used for lowering the soil pH are ammonium sulfate and sulfur.