Question

Pollen grains posses certain chemicals and stigma also? Justify.
DO tell for what these chemicals are ?

Answer 1

Dear Student,

The outer layer of the pollen grain is known as exine which consists of sporopollenin. Sporopollenin is a chemically inert substance. The deposition of sporopollenin gives rise to gaps in the exine layer called the germ pores. Sporopollenin is known to provide protection against various biotic and abiotic stress such as UV radiation, fungal attack, desiccation, etc.

The outermost surface of stigma is coated by a secretion that is released by specialized cells known as papillae. This extracellular fluid is called as stigma exudate which consists of water, sugar, lipids, proteins, phenols, amino acids and calcium ions. As the pollen grain falls on the stigma, these secretions break the outer layer of pollen i.e exine and thereby, the growth of pollen tube is initiated.

Regards