Pollen, Pollengrains and their structure

 

Pollengrains

Pollen Grains are formed inside the anther in microsporangia. Anther contains pollen grains and formed inside the four microsporangia. As the Anther dehisced due to dehydration, pollen grains are released in large numbers for better chances of fertilisation.

 

The four Pollen grains are formed from a single microspore mother cell. Microspores are arranged in tetrahedral or isobilateral tetrad.

In tetrahedral tetrad, the four microspores are located at the four corners if we observe from any angle ,only three pollen grains are visible. In isobilateral tetrad ,all four microspores are arranged in one plane.

In Magnolia, pollen grains are arranged in decussate tetrad, In Aristolochia, pollen grains are arranged in T shaped tetrad and in Halophila, pollen grains are found in linear tetrad.

 

Generally the pollen grains are separated from each other during release from the anther. But in Drimys and Drosera, pollen grains are not separated and stuck with each other. Such a group is called compound pollen grains. In member of Asclepiadaceae, all pollen grains collectively form a mass called pollinium.

Structure of Pollen grains

Pollen grains are spherical in shape and their size and shape  may vary from species to species. Pollen grains are covered by the two layers. These layers are called exine and intine. Exine is made up of  sporopollenin. Due to sporopollenin, Pollen grains have great significance. No enzyme or chemical can degrade the sporopollenin. Pollen grains make resistance against abiotic stress like temperature, humidity due to sporopollenin.  Pollen grains are preserved as fossils due to the presence of sporopollenin. 

Sporopollenin covers the pollen grains except at minor pore. This pore is called germ pore. Pollen Tube are germinated through this germ pore. Inner layer of pollen grains called Intine. It is made up of cellulose and pectin.

At the time of pollen germination, intine is protruded through the germ pore and gives rise to the pollen tube.

In 60 percentage of Angiosperms, pollen are released from Anther at 2 celled stage because it contain only vegetative and generative cell . In remaining species of angiosperms, generative cell divide and form two male gamete and pollen grain is 3 celled stage.

Pollen grain also causes pollen allergy in some peoples. It may cause some respiratory affliction like Asthma , Bronchitis etc. It is noted that Parthenium or carrot grass was imported along with wheat in Bharat and it causes pollen allergy at large extent.

Pollens are plant product so these can be used as food supplement in Western countries as pollen tablet or pollen syrups.

Race horses and athletes may also consume the pollens to increase the performance.