Question

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

• 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 occur in the style and stigma

Answer 1

Answer: (D)

Pollen wall is boron deficient and high levels of boron occur in the style and stigma

During in vitro pollen grain germination among inorganic substances, boron, in the form of boric acid or borate, has most dramatic effect on pollen germination and pollen tube growth. Pollen of most species are deficient in boron content. In nature, this deficiency is made up by comparatively high levels of boron in the stigma and style. When such pollen grains are grown in vitro high amounts of boron$(10-200$pp$)$ are supplied exogenously. Boron reduces bursting of pollen tubes as well as enhances percentage germination and pollen tube growth. Some of the role attribute to boron are
(i) Effect on water relationship and, thus, preventing pollen tube bursting.
(ii) Translocation of sugars.

(iii) Direct of indirect influence on enzymatic steps in the biosynthesis of carbohydrates.

So, the correct answer is 'Pollen wall is boron deficient and high levels of boron occur in the style and stigma'.