Pollen grains that would easily germinate on stigma are found to germinate in vitro, only when 10-200 p p m of boric acid is added. This suggest that

Options

A. boron accelerates protein synthesis in pollen grain
B. boron has an abrasive effect on the exine
C. boric acid serves as a solvent for sporopollenins
D. pollen wall is boron deficient and high levels of boron occour in the style and stigma.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Context**: The question discusses the germination of pollen grains on the stigma and in vitro (artificial) conditions. It highlights that pollen grains germinate easily on the stigma but require the addition of boric acid (10-200 ppm) for germination in vitro.

2. **Identifying the Role of Boron**: Boron is known to play a crucial role in the germination of pollen grains. It is particularly important for the formation and growth of the pollen tube, which is essential for successful fertilization.

3. **Analyzing the Stigma Environment**: The stigma of flowers is rich in boron, which aids in the germination process. When pollen grains land on the stigma, the presence of boron helps facilitate the growth of the pollen tube.

4. **In Vitro Conditions**: In a laboratory setting (in vitro), the natural presence of boron in the stigma is absent. Therefore, to mimic the natural conditions that promote germination, boric acid must be added to the medium.

5. **Conclusion**: The need for boric acid in vitro suggests that pollen grains are deficient in boron, which is necessary for their germination and subsequent pollen tube formation. This leads to the conclusion that the pollen wall is boron deficient, and high levels of boron occur in the style and stigma.

6. **Final Answer**: The correct suggestion is that the pollen wall is boron deficient, and high levels of boron occur in the style and stigma.

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