Biology Today - May 2018

• In contrast, true fruits develop only from the ovary.


• In few species, fruits develop without fertilisation. Such fruits are called parthenocarpic fruits. Banana is an example of
  parthenocarpic fruit.

Albuminous and non-albuminous seed

• Mature seeds may be albuminous or non-albuminous. Albuminous seeds retain a part of endosperm as it is not completely
  used up during embryo development (e.g., wheat, maize, barley, castor, sunflower). Non-albuminous seeds have no residual
  endosperm as it is completely consumed during embryo development (e.g., pea, groundnut). Occasionally, in some seeds such
  as black pepper remnants of nucellus are also persistent. This residual persistent nucellus is the perisperm.

APOMIXIS AND POLYEMBRYONY

• A few flowering plants such as some species of Asteraceae and grasses have evolved a mechanism to produce seeds without
  fertilisation called apomixis.


• There are several methods of apomictic development in seeds, two common methods are recurrent agamospermy and adventive
  embryony.


• Agamospermy is the formation of seed that has an embryo formed without meiosis and syngamy.

Agamospermy

Non-recurrent agamospermy

• The embryo is haploid and
  therefore the seed having it
  is nonviable.

Recurrent agamospermy

• All the cells of the embryo sac are diploid as it is formed directly either from a nucellar cell (apospory) or diploid
  megaspore mother cell (diplospory).


• The diploid egg as well as other diploid cells of embryo sac can grow into normal embryos.


• Formation of embryo directly from diploid egg without fertilisation is called diploid parthenogenesis, e.g., apple, Poa.


• Adventive embryony - An embryo develops directly from a diploid cell other than egg like that of nucellus and integument,
  e.g., Citrus, Opuntia. It gives rise to a condition called polyembryony or the phenomenon of having more than one embryo.
  In gymnosperms, polyembryony can also occur due to cleavage of growing embryo. It is called cleavage polyembryony.
  Occurrence of polyembryony due to fertilisation of more than one egg is called simple polyembryony while formation of
  extra embryos through sporophytic budding is called adventive polyembryony.


• Polyembryony is common in onion, groundnut, mango, lemon, orange.

3. What type of outbreeding contrivance is found in Primula?


4. What is the advantage of recurrent agamospermy over non-recurrent agamospermy?

Many : Monocots

Smart : Scattered vascular bundles

People : Parallel leaf venation

Ta ke : Threes (units of floral parts)

French : Fibrous roots

To easily remember the characteristics of monocots, the mnemonic

“Many Smart People Take French” can be used as follows:

APRIL 2018

1-c- OPSONIN 2-d- EPHYRA

3-f- TURION 4-a- PITUICYTES

5-g- RIBOPHORIN 6-h- PUTREFACTION

7-j- BLEPHAROPLAST 8-i- GRISEOFULVIN

9-e- BICOLLATERAL 10-b- POLLINIUM

Winner : Aswini Mura (West Bengal)