mrbudjoy-blog

[mrbudjoy-blog]

My favorite books in the past

I read these books in the past and still can't get them out of my mind. These books are worth a shot and totally engrossing.

(read it when I was a kid and it left a deep impact on me on family and divorce

[mrbudjoy-blog]

Embryo sac:

v P.Maheshwari  classified the embryo sac on  the  basis of no. of  megaspore nuclei

Ø Monosporic embryo sac: one nucleus. Eg. Polygonum, Oenothera

Ø Diasporic embryo sac: two nuclei. eg. Allium, nuclei fromEndymion.

Ø Tetrasporic embryo sac: four nuclei.

Development of embryo sac

The functional megaspore (chalazal) divides mitotically giving rise to 2 nucleate stage. It is followed by two more division to form 4 and 8 nucleate stage.Each nucleus from pole comes to the middle and form polar nuclei. These mitotic divisions are strictly free nuclear  followed by cell wall formation.

This is called Polygonum type of embryo sac  studied by Starsburger in Polygonum.

a)    The three nuclei gets organized at chalazal end called antipodal

b)   While other three nuclei gets organized  at micropyle called synergid and egg cell.

c)    The polar nuclei are present in the cenral cell.

This constitutes a 7 celled and 8 nucleate embryo sac.

Organization of embryo sac:

a)    Synergid: These cell possess micropyle nucleus and chalazal vacuole. Synergid lacks cell wall at the chalazal end and one synergid degenerate just with pollination. They have filiform apparatus which guides the pollen tube.  They secrete chemotropic substance that helps in the growth of pollen tube inside the embryo sac.

b)   Egg cell: They show cytoplasmic polarity and have cell wall thicker at the micropyle end. They have microplye vacuole and  chalazal nucleus. Plasmodesmata connection is present b/w synergid  and egg cell.

c)    Antipodal:

d)   Central cell: Largest cell.

Pollination: Types of pollination-

         i.            Autogamy: transfer of pollen grain b/w anther to stigma of the same flower.

Adaptation:

·       Homogamy: maturation of anther and stigma at the same time.

·       Bisexuality:  presence of both the whorls in the same flower.

·       Cleistogamy: The flower do not open at all. The anther and stigma lie very close to each other and ensure pollination in absence of pollinating agent and produce assured seed set.

·       Bud pollination: When pollination takes place in bud stage before opening. Eg. Pea, Rice .

      ii.            Geiotnogamy: The transfer of pollen grain from anther to stigma  of one flower to another.

   iii.            Xenogamy: Transfer of pollen grain from anther to stigma in different flower.

Agents of pollination:

·       Abiotic  agent:

1.    Wind(Anemophily):

 i. The pollen grains are light and non-sticky

ii. The stamen are well exposed to disperse pollen grains.

iii. The stigma are large and feathery to capture the pollen grains.

 iv. Presence of single ovary.

 v.   Flowers packed in inflorescence.

It’s common in grass.

2.    Water (Hydrophily):

Pollination by water is quite rare in flowering plant and is limited to 30 genera mostly monocots.

  i.            On the surface: (epihydrophily)

Eg.Vallisneria

The female flower has long pedicel which reaches the surface and the pollens are released by the male flower and carried passively by water current which is received by the stigma.

    ii.            Beneath  the surface: (hypohydrophily)

Eg. Zostera

The female flower is submerged under water where the pollen –ribbon shaped is released under water .

In majority, the flowers emerge above the water level surface and is pollinated by bees or wind. Eg. Water Haycinth or Water Lilly.

Biotic agent:

Insect (entmophily):

 Birds-Orinthophily

eg. Bombax, Callistemon

Bats-Chiropterophily

eg. Anthocephalus

Snakes-Ophiophily

eg.Santalum, Machelia

Snails-Malacophily

eg. Arisaema

 Outbreeding devices:

a.     Unisexuality:

·       Monocious : male and female are in same plant. It prevents Autogamy and but not geiotnogamy.

·       Deicious:

b.     Self incompatibility: inhibits the growth of pollen tube genetically.

c.      Dichogamy:

Pollen pistil interaction:

The stigma is able to recognize the right type of pollen by constant chemical dialogue b/w pollen grain and stigma. Its acceptance is followed by germination of pollen on stigma to produce pollen tube in style. The content of pollen grain move through the stigma. The generative cell divides mitotically to produce two male gamete.

Entry of pollen tube into ovule takes place through:

·       Micropyle (Porogamy): Most common type.

·       Chalaza(Chalazogamy): eg. Casurina

·       Integuments (Mesogamy) eg.Cucurbita.

The pollen pistil interaction is a dynamic process.