Class-12 , 2 [sexual reproduction in flowering plant ] chapter notes

         Chapter -2

     Sexual reproduction in               flowering plants...

:-Flower is a reproductive organ / part of plant .

:-A flower have four whorl /cycle .

Reproductive part :-1.gynoesium- innermost

                                    2.androecium

Accessory part :- 3.corolla

                               4.calyx -outermost

Typical plant :- capsella (cruciferrdx) 

Sexual reproduction in flowering plants

#Sexual reproduction in angiosperms:-

1.pre fertilization :-

                                     • male reproductive                                                 part.

                                     • female reproductive                                             part.

                                     • pollination.

2.Fertilization :- 

                                    • Double fertilization                                            and triple fusion .

3.Post fertilization :- 

                                     • endosperm                                                            formation.

                                     • embryo development.

1.Pre- fertilization:-

(a) Male reproductive structure -( Stamen, microsporangium, pollen grain).

Androcium:- 

                 |    Male reproductive part.

              Unit:- stamen

Stamen also known as :- Microsporophylls 

[Filament, connect and another form :- stamen]

•Filament:-

Long , slendrically, thread like sterile part.

•Connect:-

Connection b/w anther and filament.

:-Contain vascular connective tissue.

•Anther:-

Main and fertile part of stamen .

:- i

In typical angiosperm anther is two lobed and each lobe have two theca ,hence called it dithecous .

:- Total four theca / microsporongia (at corner ) present in the anther , called tetrasporangia.

Note :-In malraciae family (cotton , china rose, lady finger) single lobe present in the another (two theca present in this lobe ) called monothecous or bisporangiate.

:- In transversal section a typical microsporongium apper near circular to tetragonal .

:- The microsporangium is made up of four wall layer which is outer to inner epidermis , endothesium , middle layer and tapetum .

1.Endothecium :-

-It is a single cellular layer made up of thick walled cells .

-The outer wall of cells of this layer is thin while inner wall is thick .

-

-celluosic thickning present in radial / tangential wall of there cells .

-callose band is also deposited in this wall .

-At some places alpha- cellulose thickning and callose band are nor present on stomium.

-Endothesium is hygroscopic in nature (water obsorbing)

-Endothesium resposible of deniscence of anther (pollen grain) .

-It is also known as fibrous layer .

3. Middle layer:- 

-It present just bellow the endothesium.

-It is made up of 1-3 cellular wall made up of parenchymatous cell.

-The main function of this layer is storation of food .

-It is ephemeral (short lived ) in nature.

-Before degeneration it transfer store food into tapetum .

-It is absent in nature anther.

Pollen grain:-

                       Protect pollen grain from Uv-rays help in adnesion with insect .

Sporopollanine :-

                      Hardest material of plant kingdom .

#Tapetum:-

There are two types -

1. Amoebiadal tapetum:-

Lower plants present 

2. Glandular tapetum:-

Higher plants present

- It is innermost layer of the microsporangium.

- It nourisnes the developing pollen grain .

- The cells of tapetum posses dence cytoplasm and generally have more than one nucleus .

Note:- tapetum cells become multinucleated ( mostly binucleated and tetraploid due to endomitosis process.

:- Tapetum layer clegenerate after providing the nourishment.

(Just before difference of anther)

#Function of tapetum:-

:- Tapetum provide nutrition to developing microspore and microspore mother cell.

:- Tapetum provide growth hormone (auxine-IAA) and cottage callose enzyme .

:- Tapetum secrete sporopollanine , which forms the exine of pollen grain.

:- Tapetum secrete ubisch granule.

:- Tapetum secrete pollen kit of pollen grain (oily layer) 

#Microsporogenesis:-

                                Formation haploid microspore ( pollen grain ) by diploid pollen mother cell / microspore mother cell through meiosis division.

- Initially all microspore of a tetral remain fuse to each other by the help of callose .

- Tapetum secreate callose enzyme, which disociate callose and microspore become free to each other .

- In callotropis ( asclepediceue family ) all pollen grains of microsporangia glued together and form a group called polinium.

- In typha and clrossera pollen grain remain attach in the form terrad compound pollen grain.

#Pollengrain :-

[Study of pollen grain:-polynology]

:- Pollen grains are generally spherical meusing about 25-50 um in diameter.

:- Pollen grain has prominent two layer walled.

:- The outer hard layer is known as exine which is made up of sporopolline( most resistant organic material)

:- Sporopollanine not degrade be any known enzyme and it is resistant against high temperature and strong acid and alkyl .

:- Pollen grain exine has prominent appurture called gumpore when sporopollanine is absent ( pollen tube release from this site )

Note :- pollen grains are well preserved as fossils because of the presence of sporopollanine.

:- The inner wall of pollen is intinit is a thin and continuous layer made up of cellulose and pectin .

:- The cytosplasm of pollen grain is surrounded by plasma membrane.

:- The mature pollen grain contain two cells large vegetative and small germinating .

Note :- In pollen grain of dicot plant zerm pores are present called tricolpate while in pollen grain of monocot plant single germspore is present called monocolpate .

#Dehisence of anther :-

:- During the maturation of anther changes takes place in the wall of anther .

:- At the beginning middle layer degenerate due to absorption of food to Tapetum .

:- In mature anther only two layer epidermis and endothecium are present in the form of covering because Tapetum also degenerate after nourishment.

:-Now both pollen sac of each lobe fuse together and form single pollen sac, therefore only two pollen are present in nature anther .

:-During the dry season waterlosses occurs from the cells of endothecium.

:-Now the wall of endothecium cells contract due to loss of water inner and radical wall do not contract due to presence of fibrous thickning where is outer thin wall become contract .

( Curved inward and concave shape )

:-Incurving of outer wall exert pulling force or tension over the entire surface of anther due to the pulling force or tension thin wall containing stomial cell break off and dehisence of anther takes place ( Pollen release from anther)

NOTE :- Dehisence of anther in of angiosperm is longitudinal.

Eg:- dhatura , Capsella.

#POLLEN VIBALITY:-

:-Ability to germination of pollen grain is known as Pollen vibality.

:-Pollen grain of wheat and rice loss the vibality after 30min of releasing but the memer of rnogaceue, solanace, leguminace, maintain the vibality for a month .

:-The perial for which pollen grain remain viable is highly variable and depends on temperature and humidity .

# POLLEN PRODUCT( SYRUP & TABLET )

:- Pollen green are rich in nutrient in recent time Pollen tablet used as food substance .

:- In western countries large number of POLLEN product in the form of tablet and syrup are available in market .

:- Pollen Consumption has been claim to increase the performance of Arhlete AND Race horse .

:- Pollen also used as preparation of cosmotic product .

# AERO ALLERGAN                          ( POLLEN ALLERGY):-

:- Pollen grain of some plant cause allergy (coughing / sneezing) asthma .

Eg:- Chinopodium, parthenium ( carrot grasses) , amaranthus, sorynum, etc .

NOTE :- pollen grain of ambrocia grass cause high fever.

:- Parthenium import in India as contaminent along with wheat .

:- In cyapracea family only one pollen grain produce from one pollen mother cell.

:- largest pollen :- mirabilis galapa.

:- longest pollen :- zostera (sea grasses) .

:- Smallest :- myasotis alpesris.

# CYAPRESERVATION :-

Pollen grain store in liquid nitrogen in -196°C for long time.

# DEVELOPMENT OF MALE GAMETOPHYTE :-

 :- Haploid pollen grain conside as first cell of male gametophyte stage.

 :- The development of male gametophyte occurs in two stages.

1] Insitu development / pre pollination development :-

:- This development of male gametophyte occurs inside the anther before the pollination called insitu devlopment .

:- Haploid pollengrain undergoes unequal nuclear division resultant on small [generative nuclous] and other large irregular [vegetative nucleus ] are formed .

:-both nucleus surrounded by dense cytoplasm .

:- After nuclear division unequal cytokinesis also takes place resultant generative [ small ] and vegetative [ large ] cells are formed .

:- The vegetative cells has abundant food reserve and a large irregular shape nucleus . while in generative cell dense cytoplasm and small nucleus is present .

:- Generative cell enter into the cytoplasm of vegetative cell and float in it .

:- Generating cell shape :- spindle shape 

                                         [ vermiform shape ]