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.

Answer

D

Explanation

During in vitro pollen grain germination among inorganic substanes, 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 dificient 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 (10-200p pm) are suppied exogenously. Boron reduced bursting of pollen tubed as well as enhances percentage germination and pollen tube growth. some of the role attributed to boron are:
(i) Effect on water relationship and, thus, preventing pollen tube bursting.
(ii) Translocation of sugars.
(iii) Direct or indirect influence on enzymatic steps in the biosynthesis of carbohydrates.