ACME SMART PUBLICATION
- Books Name
- A TEXT OF BIOLOGY - CLASS XII
- Publication
- ACME SMART PUBLICATION
- Course
- CBSE Class 12
- Subject
- Biology
DOUBLE FERTILIZATION
Pollen tube enters the degenerating synergid and bursts, thereby releasing two male gametes. One
male gamete fuses with the egg to form diploid zygote. This fusion is called syngamy or
generative fertilization.
The other male gamete fuses with secondary nucleus (2n, i.e., fused polar nuclei of both polar
nuclei) to form primary endosperm nucleus (3n). This fusion is also called triple fusion because
three nuclei takes part in this fusion. It is also known as vegetative fertilization or
pseudofertilization or trophomixis.
Since two types of fusions, i.e., syngamy and triple fusion take place in an embryo sac the
phenomenon is termed double fertilisation. This event occurs in flowering plants only. Five nuclei
are involved in double fertilization.
Concept Builder
(i) The syngamy was discovered by Strasburger.
(ii) Triple fusion and double fertilization was discovered by S.G. Nawaschin and Guignard in Lilium and Fritillaria.
(iii) Entry of more than one pollen tubes in an ovule leading to the occurrence of supernumerary male nuclei (polyspermy).
(iv) When two pollen tubes enter an ovule and release their contents, it is possible that the egg may be fertilized by male gamete from one tube and triple fusion may involve participation of male gamete from another tube. This phenomenon is called as heterofertilization, e.g., Zea mays.
(v) When the entry of male gamete is not accompanied by fusion,the phenomenon is called as semigamy.
(vi) X-bodies are darkly stained DNA containing bodies found in synergid receiving pollen tube.
(vii) The percentage of pollen germination and tube growth is better in larger populations. This is referred to as "population effect" or "crowding effect".
