When the plants are grown in magnesium deficient but urea rich soil, the symptoms expressed are:

Options

A. Yellowish leaves
B. Colourless petiole
C. Dark green leaves
D. Shoot apex die

Answer

**Step-by-Step Solution:**

1. **Understanding the Nutrient Deficiency**: The question specifies that the plants are grown in magnesium-deficient soil. Magnesium is an essential nutrient for plants, playing a crucial role in various physiological processes, including photosynthesis.

2. **Role of Magnesium**: Magnesium is a key component of chlorophyll, the green pigment in plants responsible for photosynthesis. It also serves as a cofactor for many enzymes involved in metabolic processes.

3. **Effects of Magnesium Deficiency**: When plants lack magnesium, they cannot produce enough chlorophyll. This leads to a condition known as chlorosis, which is characterized by yellowing of the leaves.

4. **Impact of Urea**: Urea is a source of nitrogen, which is vital for plant growth and development. However, if the soil is deficient in magnesium, the application of urea will not alleviate the symptoms of magnesium deficiency. The nitrogen from urea cannot compensate for the lack of magnesium.

5. **Symptoms of Deficiency**: The primary symptom of magnesium deficiency in plants is yellowing of the leaves (chlorosis). Other symptoms may include colorless petioles and stunted growth, but the most prominent and immediate symptom is the yellowing of leaves.

6. **Conclusion**: Given the options provided in the question, the correct symptom expressed by plants grown in magnesium-deficient but urea-rich soil is **A: yellowish leaves**.

**Final Answer**: A. Yellowish leaves

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