Pollen pistil interactions & Double fertilization.

Good morning class. Today we will achieve the following learning outcomes:-
Students will be able to -
1) Define various outbreeding devices used by plants to prevent self pollination.
2) Elaborate about pollen pistil compatibility interactions.
3) Explain double fertilization process in plants.
4) Analyse the new plant breeding technique for Artificial Hybridisation.


I will be sharing with you all at the end of explanation the YouTube video link to have better clarity of the process.
Kindly write these notes in your register.

         OUTBREEDING DEVICES.

We know most of the plants undergoes self pollination. This could result in INBREEDING DEPRESSION in a plant species , i. e  plant decrease it pollen grain count & it may result in poor productivity of seeds.

So to overcome these inbreeding depression, plants by default has developed certain outbreeding devices.

Some of these devices are :-
A. DICHOGAMY -  In this process plant anthers & stigma matures at different time.
This is of 2 types -
 I. Protandry - Anthers are released before stigma reaches maturity.
II. Protogyny - Stigma matures prios to the pollen released.

B. HETROSTYLY / HERKOGAMY - in this process the style is longer than the anther filament or anther filament is longer than pistil.

C. SELF - INCOMPATIBILITY/ SELF STERILITY - it prevents self pollen from the same flower or different flower borne on the same plant from Germinating or developing a pollentube, a move that prevents fertilization of the egg.

D. POLLEN PREPOTENCY - in certain plants like Dolichos, this mechanism allows the pollen from another plant of the same species to germinate earlier than the pollen of the same flower.

E. UNISEXUAL FLOWER - in certain plants there are unisexual flowers which are borne on different plants or maybe different branches of the same plant. This prevents autogamy.

     

POLLEN PISTIL INTERACTIONS

So far to date, genes specifically associated with pollen germination has not been identified. But it is observed that if compatible pollen falls on stigma, then stigma provides the pollen with water & necessary medium in the form of exudates for the pollen tube germination. The exudates are highly  viscous, refractive & adhesive. These are rich in lipids, small amount of free sugars, amino acids, proteins & peptides.

---> The digestion of the cuticle of stigma allows the tube to enter the pecto - cellulosic wall of papillae & finally pollen tube grows  from the germ pore area & the tube is the extension of INTINE, through stgma & reaches towards style.

----> Once the pollen tube germinates from stigma, it undergoes style specific interactions, where style provides nutrition, growth & guidance of the pollen tubes towards the ovary.


IMPORTANCE OF POLLEN PISTIL INTERACTIONS :-



Just giving you all the basic event sequence in pollen pistil interaction 

P. S. When  the Pollen tube is extending in the style  then both vegetative & generative cells comes in the pollen tube. Generative cells divide into 2 male gametes while vegetative cell degenerates. 

DOUBLE FERTILIZATION IN PLANTS. 

1. The two male gametes enters the egg apparatus from the micropyle end via a filliform apparatus. It is at this stage the two male gametes are released in synergids.. 

2. One fuses with the egg cell to form  

ZYGOTE -----> EMBRYO 

3. The other fuses with the polar nuclei to form PEN ( Primary Endosperm Nucleus. 

https://images.app.goo.gl/PoSML6mAEYge8FLg9

One more Advantage of pollen pistil interactions are with plant breeders, where they use ARTIFICIAL HYBRIDISATION Teachinques to grow desired kind of plant. 

This technology requires following two important steps :

I. EMASCULATION - in cases of bisexual flower anthers are removed with forceps before they matures. 

II. BAGGING - in this a small butter paper bag is used to cover the flower that is emasculated to prevent contamination of the flower. 

The plant breeders dust desired pollenbgrains on the stigma of the bagged flower thus resulting in a artificial Hybridisation process.

I will be sharing the video for better clarification on your official watsapp group. 

Kindly make the notes for today. Also ask your doubts related to the topic taught  on the blog. 

See you now on 1st April  according to our Bio period in the DAY 1 time table.