Pollen germination, storage and allergy

Pollen germination

          

Pollen germination is the first step of fertilization. It requires moisture. Few seconds to few minutes are required for hydration. It causes rapid metabolite activities and following changes take place in the cell-

1. E.R. folds become free.

2. Production of vesicles increases.

3. Formation of a thin callose layer.

4. Ribosomes get aggregated into polysomes.

5. Increased lamellation in plastids.

6. RNA transcription starts.

           

The exine of the pollen grain ruptures and the intine comes out in the form of a small tube. This is the pollen tube. Factors that influence pollen germination are Hydration, Carbohydrates, Boron, Calcium, enzymes such as cellulose, pectinase and callase, temperature (20-30 C) and humidity.

 Pollen tube growth and guidance

       

 The pollen tube usually comes out at the germ pore region in a pollen grain. The entire cellular contents migrate into the tube. Growth of the tube is in apical portion, where most of the cytoplasm is located. A large vacuole fills the pollen grain and basal portion of the pollen tube. A series of callose plugs are formed from the inner side of the wall in the basal portion, to stop the backflow of the cytoplasm. The tip of the pollen tube is called as Cap block, it has very few cell organells.

        

 Chemically, the wall of the tube is made up of pectocellulosic substances. Path of the pollen tube is guided by tissue secretions of stigma and style. Chemotropic substances secreted by micropyle, are helpful in entering the tube into embryo sac, where it bursts in a few seconds and then stops to grow.

Pollen storage

            

During hybridization process, if male parent is situated at a long distance or it matures earlier than female parent; the pollen grains are stored at low temperature in controlled humidity, and utilized as and when needed.

Pollen allergy

            

During their path from anthers to stigma pollen grains become air borne. When sensitive people inhale them, they secrete certain chemicals, when they come in contact with the mucuous members of nose, eyes and mast cells present on skin. These chemicals excite the immune system to produce specific antibodies, which causes higher production of histamine. Due to which symptoms like breathlessness, redness of eyes rashes on skin may occur. These are termed as pollen allergy. Common pollen allergenic pollen are pollen grain of grasses, amaranths, chenopods, Parthenium, Eucalyptus , Cassia.