POLLEN GRAIN STRUCTURE, VIABILITY, ALLERGY & PRODUCT

 

STD-12      UNIT-6   CHA-2

REPRODUCTION IN FLOWERING PLANT

POLLEN GRAIN STRUCTURE, VIABILITY, ALLERGY & PRODUCT 

• Structure of Pollen Grain 

• It is commonly globular in outline , though several other shapes are also found . 
• The diameter is 25-50 micrometer . There is a highly resistant wall on the outside and cellular contents inside .
• Its cytoplasm is rich in starch and unsaturated oils . 
• The latter protect the chromosomes from radiation damage .
• Pollen grain protoplast is uninucleate in the beginning but at the time of libera tion it becomes 2-3 celled . 
• Wall or covering of pollen grain is called sporoderm . 
• It has two layers , outer exine and inner intine . 

• Intine is pecto - cellulosic nature . At places it contains enzymatic proteins ( Knox and Heslop - Harrison , 1971 ) . 
• Exine is made of a highly resistant fatty substance called sporopollenin ( Zelisch , 1932 ) . Sporopollenin is not degraded by any enzyme . 
• It is not affected by high temperature , strong acid orstrong alkali . Because of the sporopollenin , pollen grains are well preserved as microfossils . 
• The study of external morphology of mature pollen grains is called palynology . 
• In insect pollinated pollen grains the exine is spiny as well as covered over by a yellowish , viscous sticky and oily layer called pollenkit . 
• Pollenkit is made up of lipids and carotenoids . 
• At certain places the exine is thin or absent . 
• The areas may have thickened intine or deposition of callose . They are called germ pores ( if rounded ) or germinal furrows ( if elongated ) . 
• Pollen grains are generally tricolpate ( with three germ pores ) in dicots and monocolpate ( with single germinal furrow ) in monocols

• Pollen Viability 

• It is the period for which pollen grains retain the ability to germinate Pollen viability is little in flowers which are pollinated in bud condition .
• It is 30 minutes in Rice and Wheat . 
• In others the period of viability is long , even months in some mem bers of family rosaceae , leguminosae and solanaceae . It , however , depends upon envi ronmental conditions of temperature and hu midity . 
• It is possible to store pollen grains for years in liquid nitrogen ( - 196 ° C ) in pollen banks for later use in plant breeding programmes .

• Pollen Allergy . 

• Pollen grains are produced in large number , especially in anemophilous spe cies . 
• They float in air and enter respiratory tracts . 
• Some individuals develop allergy to them , producing respiratory disorders like rhinitis , asthma and bronchitis , bronchial allergy ( Hay Fever ) 
• The major contributor to pollen allergy is Carrot Grass , Parthenium . 
• It entered India as contami nant with imported Wheat but has spread in all parts of the country . 
• Chenopodium , Amaranthus Sorghum , Ricinus , Prosopis , Cynodon are other common sources of pollen allergy . 
• Since different plants produce pollen grains in different sea sons , pollen calenders of atmosphere can be scanned and the allergic reaction pinpointed to particular plants . 

• Pollen Products . 

• The pollen grains especially the ones collected by Bees are being used for a variety of purposes like nature cure , cosmeticsand as food supplements.
• Pollen grains are believed to be rich in nutrients ( Protein 7-26 % , carbohydrates 24-48 % , fats 0.9-14.5 % ) . 
• They are taken as tablets or syrups to improve health , enhance performance of athletes and race horses .

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