polyembryony

1. PATNA UNIVERSITY
DEPARTMENT OF BOTANY
A SEMINAR PRESENTATION ON
“ POLYEMBRYONY”
SUBMITTED TO: SUBMITTED BY:
Dr. MEENAKSHI SINGH ALKA KUMARI
HOD, DEPARTMENT OF BOTANY ROLL NO.- 04
PATNA UNIVERSITY M.Sc. BOTANY
SEMESTER –II
SESSION: 2020-22

2.  Introduction
• Polyembryony can be defined as the occurrence
of more than one embryo in a seed.
• The first case of polyembryony was reported in
certain orange seeds by Antonie van
Leeuwenhoek(1719).
• Polyembryony is quite common among conifers
(Gymnosperms) but many species of both
dicotyledons and monocotyledons exhibits this
phenomenon.

3.  Classification
• Ernst and Schnarf classified the polyembryony
into two types:
1. True polyembryony
2. False polyembryony
• True polyembryony may be sub-divided into
two types:
a. Cleavage polyembryony
b. Adventive polyembryony

4. 1. True polyembryony
• The production of embryos within or by
projecting into a single embryo sac is termed
as true polyembryony.
Fig: Cleavage polyembryony

5. a) Cleavage polyembryony
• Where the embryos arise within an embryo
sac either by a cleavage of the egg or from the
synergids , antipodals or endosperms.

6. b) Adventives polyembryony
• Where the embryos arise from the tissue lying
outside the embryo sac.
• The cells of the nucellus or the integuments but
generally they come to lie within the embryo sac.

7. 2. False polyembryony
• Multiple embryo sacs in
an ovule may arise from:
a) Derivatives of the same
megaspore mother cell
b) Derivatives of two or
more megaspore
mother cells
c) Nucellar cells

8.  Causes of polyembryony
• Many theories have been proposed to explain
the occurrence of polyembryony by different
workers.
• Some of the important theories are as follows:
A) Necrohormone theory:
• Haberlandt(1921,1922) proposed the
“Necrohormone theory”. He regarded the
degenerating cells of the nucellus as source of
stimulus for the adjacent cells to divide and
form adventive embryos.

9. B) Hybridization theory
• According to this theory the occurrence of
multiple embryos is due to hybridization.
• The recombination of genes takes place
during the process of hybridization, forming a
single unit that gives rise to the multiple
embryos.

10.  Importance of polyembryony
• Plant breeding and horticulture.
• Nucellar embryos are supposed to be free from disease.
• Propagation of the fruit tree, such as Citrus and Mango.
• The application of adventive embryos is also important for
providing genetically uniform seedlings of fruit trees.
• Can be used for the development of homozygous diploid

11.  Disadvantages of Polyembryony
• It constitutes problem in crop improvement because it
makes the identification of hybrids, particularly in crosses
involving taxonomically closely related parents.
• Loss of vigour of zygote embryo due to suppression by the
nucellar embryos during seed development.
• Germination of monoembryonic seed is low due to the
competition between the embryos in a single seed.
• It reduces the variability since nucellar seed will have the
same genotype as the parental genotypes.