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Sex.rep.flo.plants

Sexual Reproduction in flowering plants| digitalnotes

11 minute read

Index:-
  • pre fertilization events
  • fertilization events
  • post fertilizarion events

Pre fertilization events

(i)Flower (Flower parts)

(1)Male reproductive part = microsporophyll( Micro=small,spore=spore,phyll=leaf)
(2)Female reproductive part = megasporophyll( Mega=big,spore=spore,phyll=leaf)

+microsporophyll, microsporangium, microsporongia, microspore+
-Microsporangium (plural = microsporangia)
-Megasporangium (plural = megasporangia)

(a)Microsporophyll

anther
bilobed & dithecous condition

T.S(transverse section) of anther
contain 4 microsporangia(pocket like structure,filled with microspores)

Note:- unilobed or monothecous - bisporangiate condition - Malvaceae family

layers of anther wall:-  
Epidermis
-protection

Endothecium
-Radical wall of endothecium alpha -  cellulose fibrous layer is present.
-it provide strength to the cell.

{stomial cells=stomium cells}
At the corners of anther stomial cells, are present, where these fibrous layers are (-)nt(absent).
From stomium cells, anther  walls ruptures at the time of release of pollen grain. Hence,if froms the lininig of dehiscency.

Middle layer
-short lived as they consume to provide nutrition  to the developing microspores.

Note:-
Epidermis,endothelium and middle layer collectively provide nurishment and protection.

Tapetum

-nutritive layer
-innermost layer
-polyploid and multinucleated  cells
 
Type of taptum:-
Amobiodal teptum 
-cell wall of teptum degenerated.
-remaining cell shead off into microsporangia to provide nourishment to sporogeneous tissue.
-Also k/a Plasmodal taptum

Serectry taptum
-cell wall persists 
-nutrition secreted into microsporangia
-Also k/a glandular tapetum

Function of Teptum
-1)Formation of callose enzyme
-2)Involved - formation of -exine

Exine
  • --sporopollenin
  • -spoeopollenin formed by oxidative polymerisation of carotenoid  derivation.
  • -sporopollenin hardest substance as shows resistance to:-
    • --High temp.
    • --strong acid
    • --strong alkali

-No biological enzyme discovered,--degrade sporopollenin.
-thus preserved as a fossils.

3)Forms pollen kit over pollen grain
4)Formation of proteins over pollen grain
 

Microsporogenesis

-MMC(microspore mother cell)------to microspore.

key- In Aristolochia elegans 5 types of tetrad found.

These are 5 types of tetrads:-
1. Isobilateral Tetrad
2. Tetrahedral Tetrad
3. Linear Tetrad
4. T-shaped Tetrad
5. Decussate Tetrad
 
 
-microgametogenesis - formation of gamate
-Vegetative cell/Generative cell
-vegetative cell-- pollen tube 
-generative cell-- produce 2 male gamete

 
Pollen grain(25-50 um)
-study of pollen grain - polynology

key- layers of pollen grain is known as sporoderm.

Sporoderm
- outer layer- exine
-inner layer- intine(streachable - pollen tube formation)

Note:-
1)Pollen grain contain reserve food,nutrious,hence utilised by atheletes.
2)Viability-time period - pollen grain contain ability to germinate- after releasing from anther.(wheat,rice,maize - 30 min)(solanaceae,malvaceae- few months)
3)cryopreservation of pollen grain occurs at - 196*c in liq N2.

button

Female reproductive system
pistil/carpel = Megasporophyll

Number of carpel
1)Monocarpellary
2)Polycarpellary fused- syncarpous(tomato,tulip),free - apocarpous(rose,lotous)

Ovule
1)1 ovule
2)many ovule

Types of ovule:-
1)Orthotropous 0* (Mostly primitive,all gymnosperms,few angiosperms)
2)Anatropus 180*
3)Hemi - anatropous 90*
4)Campylotropous >90*(more than 90*)
]]5)Amphitropous(embryo sac - also bend like hourse shoe shape.)
6)circinotropous

*dont forget to give examples

Megasporogenesis

-formation of Megaspore from MMC(megaspore mother cell)

**Archesporial cell = megaspore mother cell.

megasporogenesis image

Megagametogenesis - formation of embryo sac(female gametophyte)
female gametophyte or embryo sac = (3+2+3)=Nuclei arrengement,it is 7 celled- 8nucleated structure. 

egg aparatus = 1 egg cell + 2 synergid cell(helping cell)
**cytoplasm of egg cell & synergids are contineous with the help of plasmodesmata.

Filliform Aparatus
-finger like projections in synergid cells
-helps in entry of pollen tube in embryo sac.

having three functions:- cns
c- chemical guidence to pollentube
n-provide nourishment to developing pollen tube.
s-provide mechanical support.

Polar nuclei
-both nuclei fuses to form secondary nucleus(2n).

Antipodal cells 
-function is unknown.🤣
-dgenerate during fertilisation of gamete.

1)Find out number of mitosis & meosis required for the formation of 800 male gametes from a stamen of a flower?

2)Find out number of mitosis and meosis required for the formation of embryo sac in  a  plant from MMC?

Note:-
1)Raphe:-
rigid formed b/w ovule and funicle.- Raphae

2)Aril:-
Arile or third integument.
Litchi - has third integument,which is edible

3)Obturator
Physical barrier arise from funicle to help pollen tube to move towards micropyle.

(ii)pollination

Transfer of pollen grain - to stigma

3 type 
1)Autogamy(self fusion)- pollination occurs in same flower.
2)Geitonogamy(Neighbour fusion)- different flower of same plant.
3)Xenogamy(foreign/Alien fusion)- different flower of diff. plant of same species

Adaptation by flower for self pollination

1)Cleistogamy:-
-Flower that never opens(i.e. Anther is absent)
-such flower is called cleistogamous flower-
eg.
-commelina
-oxalis
-viola
-Arachis hypogea (ground nut)

cleistogamous vs chasmogamous

cleistogamy flower
1)Anthesis (- nt)
2)Only  self pollination
3)underground/Arieal
4)Dull colour

chasmogamous flower
1)(+ nt)
2)self/cross
3)Always aerial
4)dull / bright

*In cleistogamous flower one advantage is assured seed  set.

2)Bisexual flower(monocliny)
Pistil and stamen both present in same flower.
eg:-
catharannthus 

3)Homogamy
Male and female part both mature at same time.

4)Bud pollination
pollination occurs in bud stage(i.g) pisum sativum,wheat,rise,maize

Adoptions by flower for cross pollination

1)Dicliny:-(unisexual flower)
a)dioecious(male/female in other plant) - papaya,date palm,mulberry
b)Monoecious(male/female in same plant)- Coconut

2)Dichrony - male and female part mature at different time
protandry - Androecium mature 1st(eg. sunflower,cotton,salvia .etc)
protogynas -gynoecium mature 1st(eg.ficus,aristotochea etc.)

3)Herbogamy
Physical barrier develop in b/w male/femal resp. - to avoid self pollination.
eg.Translator apparatus in case of calotropis.

4)Heterostyly:-
Different size of pistil and stamen.
eg:-
brinjal etc.

5)Prepotency:-
germ.n of fore.n pollen grain is faster as compare to germination of self pollen grain.eg:-Apple,Grapes

6)self incompatibility:-
inhabit(stop) germ.n of self pollen grain while promote germ.n of diff. pollen grain of same species.

Pollinating Agency

(iii)pollen - postil interaction

Double fertilization:-
-polar nuclei+male gamet = PEN(primary endospermic nucleus)
-egg or female gamete or oosphere +male gamet =(syngamy)= zygote or oospore(2n)
-degenerating synergid(side one)

Note :-
2 fertilization occures i.e triple fusion & syngamy.Hence called double fertilization.

Post fertilisation Events:-
1)endosperm development
2)embryonic development
3)seed for.n
4)fruit for.n

Endospermic development:-
-it occurs prior endosperm development - provide nourishment for the development of embryo.

3 type-
1)Free Nuclear type-(coconut milk [liq.part ])
2)cellular type(coconut copra[white solid])
3)Helobial type(orden helobiales)

image

Chemical nature of endosperm:-

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