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Prof A. B. Deshmukh's Biology Class

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1. REPRODUCTION IN LOWER & HIGHER PLANTS

-CREATED BY-

PROF. DESHMUKH A. B.

ASST. TEACHER

SEC. & HIGHER SEC. SCHOOL, SHENDI (BHANDARDARA DAM), TAL. – AKOLE, DIST. - AHMEDNAGAR

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1.9 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.

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  • It usually enters ovule through the micropyle.
    • It is termed as porogamy.
  • But in some cases, it is found to enter through chalaza, known as chalazogamy ,
  • In some plants by piercing the integuments, called mesogamy.
  • Finally, it penetrates embryo sac of ovule through its micropylar end.

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  • 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.

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  • Syngamy is the fusion of haploid male gamete with haploid female gamete (egg) to produce a diploid zygote, whereas in triple fusion, second haploid male gamete fuses with diploid secondary nucleus producing primary endosperm nucleus (PEN) that develops into triploid endosperm.

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  • 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.

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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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