Polyembryony , Its type and example

• In plants, polyembryony wasfirst reported by Anton von Leuwenhoek in orange.

• The occurrence of more than one embryo in ovule or seed or fertilised ovum is termed polyembryony.

• In several gymnosperms, polyembryony is frequently seen.  

• In some species of plants, a diploid egg cell is formed without reduction division and developed in embryo without fertilization.

• In Citrus and Mango, some of the nuceller cells around the embryo sac, start dividing and protrude in to embryo sac and develop in to embryo.

• In citrus, each ovule contains many embryo.

• In the majority of the gymnosperms there are two or more archegonia present  in a female gametophyte so each archegonium contains two or more eggs.

• During the fertilization, two or more eggs are fertilized. As a result, two or more  embryos are developed.  But only one embryo is flourished  and remaining embryos are degenerated  during the development.

• Polyembryony is of  two types

Types of polyembryony

• Induced Polyembryony comprises experimentally or artificially polyembryony that is induced externally.

• Spontaneous Polyembryony is natural polyembryony.

• Webber  described the process of polyembryony into three types. 

• Cleavage Polyembryony is the development of the number of embryos  from a single fertilized egg.Ex- Gymnosperm.

• Simple Polyembryony is the development of the number of embryos  due to  fertilization of more than two archegonia. For Ex- Brassica Rosette Polyembryony is the development of additional embryos from the rosette cells. Ex-Pinus.

• Adventive polyembryony is development of the embryo from the cell of nucellus or integuments. Ex-Mangifera and Opuntia.

👌👌Remember Polyembryony is also marked in several order of gymnosperms like Cycadales, Coniferales Taxales Gnetales. 

Theories of polyembryony

• There are various theories to explain the polyembryony.

• These theories also reveal about the cause of polyembryony.

• According to the Necro hormone Theory, nucellus is degenerated, this degeneration induces adjacent cells to undergo repeated division and form many embryos.

• This theory explains the formation of adventive embryos. 

• Hybridisation Theory leads  to recombination of genes where a single unit is formed, which creates multiple embryos.

• The Significance of Polyembryony are as -

• It is particularly useful for the propagation of certain species of plants. 

• Adventive embryos retain characteristics of the parent plant, and are used to create genetically uniform seedlings of citrus and mango.

• In the case of citrus, grafts from other types are also used in building of  stock.