Question

Pollen grains that would easily germinate on the stigma, are found to germinate in vitro, only when 10-200ppm of boric acid is added. This suggests that
A. Boron accelerates protein synthesis in pollen grain
B. Boron has an abrasive effect on exine
C. Boric acid serves as a solvent of sporopollenin
D. Pollen wall is boron deficient and high levels of boron occur in style and stigma

Answer 1

Pollen grains are male gametophytes of seed-bearing plants. It is covered by an inner coat called intine and a hard outer layer called exine. The exine is made up of sporopollenin. The germination of pollen grain requires certain organic and inorganic substances.

Complete answer:
Germination of a seed is the process by which the seed develops into a seedling under favorable conditions of temperature, humidity, water and oxygen.
If a seed is artificially germinated in a laboratory under proper conditions, the process will be known as in-vitro germination.
The role of boron in plants is widely studied. Several researches have shown that boron is indispensable to plant growth. It is much more important for reproductive growth rather than vegetative growth.
However, pollen grain of most plants is boron deficient. This deficiency is made up by high concentrations of boron in style and stigma. Thus, the supply of boron is maintained in plants throughout the period of germination of pollen grains. Boron is required to prevent the pollen tube from bursting, helps in translocating sugars, and aids to bring about various biochemical reactions.

Therefore, option (D) is correct.

Additional Information: Boron is an important micronutrient in plants. It helps to maintain the integrity of the plant cell walls and regulate certain metabolic pathways in plants. Boron is present in water soluble and insoluble forms in plants. It is the lack of water-soluble boron that accounts for boron deficiency. The optimum boron content is about 20-100ppm. Excessive boron concentration can lead to toxicity in plants.

Note: Pollen grains bear the male gametophyte. The pollen covering protects the sperm while pollens are being transferred from the anther to the stigma. Pollen grains are transferred by a process called pollination. The process is mediated either through wind, or water, or through animals. The germination of pollen grain requires boron that is present in the style and the stigma. In vitro germination of pollen grains requires the presence of boron in the form of Boric acid. This is because pollen grains lack the micronutrient. Boron deficiency can cause infertility in plants.