01 Reproduction in Lower and Higher Plants - part 07 - Pollen - Pistil Interaction and Double Fertilization

01 Reproduction in Lower and Higher Plants - part 07 - Pollen - Pistil Interaction and Double Fertilization


Pollen - Pistil Interaction : 

  • It is the interaction of pollen grains with sporophytic tissue (stigma). 
  • It begins with pollination and ends with fertilization. 
  • All the events from the deposition of pollen grain on stigma to the entry of pollen tube in the ovule (synergid) are referred as pollen - pistil interaction.
  •  Pollination does not guarantee the transfer of right type of pollen, often wrong type also land on stigma. 
  • The pistil has the ability to recognise and accept the right or compatible pollen of the same species. Thus wrong type of pollen is discarded by pistil. 
  • Compatibility and incompatibility of the pollen-pistil is determined by special proteins. 
  • This process involves pollen recognition followed by promotion or inhibition of pollen. 
  • The stigmatic surface of flower refuse other wrong type or incompatible pollen grains.
  •  A physiologial mechanism operates to ensure that only intraspecific pollen germinate successfully. 
  • The compatible pollen absorbs water and nutrients from the surface of stigma, germinates and produces pollen tube.
  •  Its growth through the style is determined by specific chemicals. 
  • The stigmatic surface provides the essential prerequisites for a successful germination, which are absent in the pollen. 
  • The pollen tube is finally pushed through the ovule and reaches the embryo sac. 
  • The tip of the pollen tube enters in one of the synergids and then ruptures to release the contents. 
  • Due to pollen pistil interaction, intense competition develops even in the compatible pollen grains (gametes). 
  • It also plays important role in sexual reproduction and seed formation. 
  • Pollen grain can also be induced to germinate in a synthetic medium. 
  • Sucrose induces pollen germination and tube growth in vitro. 
  • Addition of boric acid facilitates and accelarates pollen germination.
Artificial hybridization : 
  • It is one of the major approaches used in the crop improvement. 
  • Only the desired pollen grains are hand pollinated and used  for fertilization.
  • This is accomplished through  emasculation and bagging procedure.
Double Fertilization :
  • Double fertilization is a complex  fertilization mechanism in flowering (angiospermic) plants. 
  • It was discovered by Nawaschin in the liliaceous plants like Lilium  and Fritillaria.
  • After a pollen grain has reached the surface of the stigma, it germinates and forms a pollen . tube, which penetrates the stigma, style, ovary chamber and then enters ovule. 
  • The growth of pollen tube is guided by the chemicals secreted by the synergids. It usually enters ovule through  micropyle. It is termed as porogamy. 
  • But in some cases, it is found to enter through chalaza,known as chalazogamy and in some plants by piercing the integuments, called mesogamy.
  • Finally, it penetrates embryo sac of ovule  through its micropylar end.
  • The pollen tube carrying male gametes penetrates in one of the synergids. 
  • Watery contents of synergid are absorbed by pollen tube which then ruptures and release the contents, including the two non-motile male gametes. 
  • As non motile male gametes are carried through hollow pollen tube, it is known as siphonogamy that ensures fertilization to  take place.
  • Syngamy and triple fusion are two  events of sexual reproduction in angiospermic flowering plants. 
  • Syngamy is the fusion of  haploid male gamete with haploid female  gamete (egg) to produce a diploid zygote.
  • Triple fusion, second haploid male gamete fuses with diploid secondary nucleus  producing primary endosperm nucleus (PEN)that developes into triploid endosperm. 
  • The zygote develops into an embryo. 
  • Syngamy is  a type of generative fertilization whereas triple  fusion is a type of vegetative fertilization. 
  • Here, both the male gametes participate  and therefore, it is described as or called double  fertilization
Significance of Double Fertilization : · 
  • It is a unique feature of angiosperms. 
  • It  ensures that the parent plant invests a  seed with a food store, only if the egg is  fertilized.· 
  • The diploid zygote develops into an embryo which consequently develops into a new  plant.
  • The triploid PEN develops into nutritive endosperm tissue. 
  • It restores the diploid condition by fusion of haploid male gamete with haploid female gamete (i.e. through syngamy). 
  • It also helps to avoid polyembryony.



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