Question

Molybdenum is involved in plant metabolism in
A. Translocation of solution
B. Nitrate reduction
C. Tryptophan synthesis
D. Ascorbic acid synthesis

Answer 1

Molybdenum (Mo), the last of the micronutrients available, is needed by plants in the smallest quantity. The normal range for most plant tissues is between 0.3-1.5 ppm and between 0.01-0.20 ppm in the rising medium.

Complete Answer:
- Molybdenum is an important component of two enzymes that convert nitrate to nitrite (a toxic form of nitrogen) and then to ammonia until it is used to synthesise amino acids within the plant. Symbiotic nitrogen fixing bacteria in legumes were wanted to repair atmospheric nitrogen. Plants can use molybdenum to transform inorganic phosphorus to organic forms in the plant.
- Since molybdenum is required to convert nitrate to ammonia inside the plant, feeding with mostly nitrate fertilizer will cause molybdenum deficiency earlier than feeding with ammonia fertilizer. Research has shown that high sulphate levels can reduce molybdenum plant uptake. Molybdenum is the only macronutrient that becomes inaccessible as the pH of the rising medium decreases.
- As molybdenum is closely related to nitrogen, its deficiency can easily imitate nitrogen deficiency. Molybdenum is the only macronutrient that is mobile inside the plant so the signs of deficiency occur on the old and middle leaves, but extends the stem and affects the new leaves.

Thus the correct answer is option(B) Nitrogen reduction.

Note: Molybdenum deficiency or toxicity is not very common, but there is a higher occurrence of molybdenum deficiency in poinsettias. Like any nutrient deficiency or toxicity, it must be fixed before there is a detrimental effect on crop growth and quality.