Sexual Reproduction In Flowering Plants

Are we not lucky that plants reproduce sexually? The myriads of flowers that we enjoy gazing at, the scents and the perfumes that we swoon over, the rich colours that attract us, are all there as an aid to sexual reproduction. Flowers do not exist only for us to be used for our own selfishness. All flowering plants show sexual reproduction.
in this slide the chapter explanation is according to NCERT Syllabus which would be helping students in every field..

1. Sexual reproduction in flowering plants Chapter -2 NCERT By- Punya Mohanty

2. Flower-a fascinating organ of angiosperms:

3. P r e fertili z a t ion : s t ruc t u r e and e v ents: Hormonal a n d st r uctu r a l chang e s in p l ant s lead s t o d e v elopment of f l o w e r , A n d r oecium consi s t s of a w ho r l of stamens r ep r esents m a le s e x o r g an. G y n oecium r ep r esents the f e m ale r ep r oduct i v e o r g an. Stame n , M i c r ospo r an g iu m an d P ol l en g r a in: T ypical stamen consi s t s of t w o part s, long an d s l ender stalk called f i lam en t a n d t er m in a l bilob e d struct u r e called a n the r . A typi c a l an g iosperm anthe r is bilobe d . Eac h l obe h av e t w o theca i.e. dithe c ous . Eac h anthe r contains f our m i c r ospo r an g ia loca t ed a t the corners, t w o in each lobe. Mic r ospo r a n gia b e come p o l l en sacs a n d a r e pac k ed wit h pol len g r ains

4. Struc t u r e o f mic r ospo r angium: Structu r e o f mic r ospo r angium: Eac h mic r ospo r angiu m sur r ounded b y f our w al l l a y e r s Epidermis En d othecium M i dd l e l a y e r . T apetum . The in n e rmost l a y er is tapet u m w hich is m u lt i nuclea t ed, w i t h de n se cy t op l asm ; it nourishe s the d e v eloping po l le n g r a i n. The cen t e r s of e ac h mic r ospo r a n g iu m cont a in ho m oge n ous cells called spo r ogenou s tis s u e s.

5. Mic r ospo r ogen e sis : The p r ocess of f ormation of mic r ospo r es f r om polle n mothe r cell th r ou g h meiosis is called mic r o s po r o g en es i s . The spo r ogenous t i ssue of mic r ospo r angium d i f f e r ent i a t ed in t o mic r o s po r e mother c ell o r p o lle n mothe r c ell . Eac h mic r o s po r e mothe r cell unde r goe s meio s is an d g iv es rise t o hap loi d mic r o s p o r e t et r a d . O n de h y d r ati o n mic r ospo r e t et r a d d i ss o cia t ed t o f orm f our mic r o s po r e s . Eac h mic r o s po r e d e v eloped in t o a p o lle n g r ai n .

6. P ollen g r a in: P oll e n g r ain r ep r es e nt s the mal e g ame t op h y t e s . I t is spher i c a l a n d measuri n g a bou t 2 5 -5 mic r ome t er in diamet e r . I t is c o v e r ed b y t w o l a y er s . The ha r d out e r l a y er c a l l ed the e x i ne is made u p of s p o r opol l en i n , w h i ch is one of th e most r e sista n t o r g ani c mat e r i al s kn o w n . I t can w i ths t an d h ig h t e mpe r at u r e a n d s t r ong acids a n d a l k a l i . No e n zyme c an deg r ades sp o r op o l l e n in is so f ar kno w n. The e xin e has p r omin e n t a pertu r es c a l l ed germ po r e w h e r e sp o r op o l l e n in is a bs e n t . The i n n e r w a l l of poll e n g r ain is c a l l ed intin e . I t i s th i n a n d c o ntinuou s l a y er mad e of c el l ulos e an d pecti n . O n mat ur i ty the poll e n g r ain c o nt a i n s t w o cel l s, t he v eg e tat i v e c ell a n d ge n e r at i v e c el l . The v egetat i v e cell is b i gge r , has a b u nd a n t f o o d r es e r v e a n d a la r ge i r r egula r l y sha pe d nucl e us. The ge n e r at i v e cell is sma l l a n d flo a ts in the cytoplasm of v egetat i v e cel l . I n 60 % of a ngios p e r ms , poll e n g r ai n s a r e shed at th i s 2 - c el l ed stag e . I n o t h e rs the ge n e r at i v e cell d i v i des mi t o t ical l y t o f orm t w o ma l e game t es b e f o r e poll e n g r ain a r e shed ( 3 - c el l ed stage ).

7. Ec onomi c importan c e o f p ollen g r ain: P ol l en g r a i n m a y cause s e v e r e a lle r g i es a n d b r onchial a f flict ions. I t m a y cause c h r onic r espi r a t ory diso r de r s – as t h m a , b r onchitis, e t c. P ol l en g r a i n of P a rthe n ium or car r ot g r as s causes po l le n a lle r g y . P ol l en g r a i n s a r e rich in nut r ie n t s hence use d a s polle n t able t s f or f ood s u pp l eme n ts. P ol l en consu m pt i ons in c r e a se per f ormance of a t hle t es a n d r ace horses. A f t er shedding th e v i abilit y depends on t empe r a t u r e and h umidi t y . I n w heat a n d rice th e polle n g r a i n lose vi a bili t y w i thi n 30 min . of the i r r ele as e . I n R osace ae , Leguminose a e a n d So l a n ac e a e th e y r ema i n vi a ble f or m o n ths. P ol l en g r a i n can b e p r es er v ed f or y e a rs in liqu id n i t r ogen ( - 196o C).

8. T h e P i s t il , M e ga spor a ngium ( o v u l e) a nd E m b r y o S ac : The G ynoecium r ep r es e n t s th e f emale r ep r od u ct i v e par t of t he fl o w e r . The G yno e cium m a y cont a in sing l e pis t il ( mon o carp e l l ar y ) or m a y h a v e m o r e t han one pis t il ( multicarpellar y ). F use d pis t ils a r e called s yncarpous a n d f r ee pis t ils a r e called apocarpo u s . Eac h pist i l has th r ee part s th e stigma, st y l e and o v ary . Ins i de th e o v a r y is th e o v aria n c a vity ( l o cule ). The pla c enta lo c a t ed in side th e o v a r i a n c a vi t y . Me g aspo r ong i a o r o v u les a r ise f r om th e plac e n t a. The num ber of o vule in side th e o v a r y m a y b e single o r ma n y .

9. Th e Me g asp o r angiu m (Ovul e ): O v ul e is a small structu r e a t t a c h ed t o th e place n t a of lo c ul e w i t h a s t al k ca lle d funicl e . The b o d y of th e o vu l e fused wi t h th e funicle in the r egion called hilu m . Hilum is t he j u nct i on bet w e e n th e fun i cle a n d o vule. Eac h o vule has one or t w o p r o t ect i v e e n v elops called in t eg u ment s . In teg u m e n t c o v e r ed t he o vule e x cept a n open in g a t the t op called mic r o p y l e . Opposi te of th e mic r o p y la r e nd, is t he chalaza , r ep r es e n t in g th e bas a l par t of t he o vule?

10. F emale g ame t op h y t e: Ou t of f our me g aspo r es, one me g aspo r e is funct i onal a n d other th r ee dege n e r a t es. The funct i onal me g aspo r e d e v eloped in t o th e female g ame t op h y t e . F emale g ame top h y t e is k n o w n a s t he emb r y o sa c . D e v elop m e n t of embr y o sac f r om a s ing l e me g aspo r e is called as mon o sporic t y p e of embr y o sac. The nucleu s of th e funct i onal me g aspo r e d i vid e d b y mi t otic d i visio n t o f orm t w o nuclei w hich m o v e t o th e opposi t e po le, 2 -nuclea t ed emb r y o sa c . T w o s u ccess i v e mi t otic d i vis i on le a ds t o f ormation of 4- nuclea t e a n d la t er 8 -nuclea t e sta g e s of th e e m b r y o sac. Al l mi t otic d i vis i ons a r e f r ee nuc l ea r type ; k a r y okinesi s is no t f ol l o w ed b y cy t okinesi s .

11. Si x of th e eig h t n u clei a r e sur r ounded b y cell w all s a n d o rg a n ize d in t o cells. Th r ee cells a r e g r ou ped t oge t her a t th e mic r o p y la r e nd, const itu t e th e egg ap p a r atus. The egg ap p a r a t us , in tur n consists of t w o s yne r gids and one egg c el l . S yn e rg i ds h a v e spe cial fil i for m ap p a r atus , w hich pl a y an importa n t r ole in guidi n g th e e n t ry of po l le n t u be in t o the s yne r gid s . Th r ee cells a r r a n g e d t o w a r ds c h al azal e n d a r e called antipoda l cells. The la r g e c ent r a l c e l l has t w o pola r nuclei. A t y pica l a n g iosperm embr y o sac a t maturi t y is 8- nuclea t ed and 7-c elled.

12. P olli n a t ion: T r ans f er of pol l en g r a i n s f r om th e a nth e r t o th e s t igma of a pisti l is t er m ed a s po l lination. Bot h m a le an d f emale g ame t es a r e no n - mo t il e . Kinds o f p o ll i nation: A u t o g a m y : P o l lination withi n same fl o w e r . In o pe n an d e x p o s ed anther s an d s t igma a u t o g a m y is r a r e. Vi o l a , O x a l is an d C o m m e l i n a p r o d uc e t w o typ e s of fl o w e r s: Chasmo g amou s : e xpose d anthe r an d sti g m a Cleis t o g amous : c l osed anthe r an d sti g m a. Cl e is t o g amou s fl o w er is i n v ari a b l y au t o g am o u s an d a s s u r ed see d s e t e v en in th e a bs e nc e of th e p o l lina t o r .

13. Me g asp o r ogenesi s : The p r ocess of f ormation of me g as p o r es f r om th e me g as p o r e mothe r c ell is called Me g as p o r o g ene si s . I n th e cent r e of th e o vule the r e is a m as s of t i s s ue called nucellu s . Cells of nuce l lu s h a v e abundan t r eser v e f ood ma t erials. On e cell of th e nuce l lu s t o w a r ds mic r o p y la r end d i f f e r ent i a t ed in t o me g aspo r e mot h er c ell (MMC). I t is a lar g e di p l o id c ell, den s e cy t o p las m wit h p r ominen t nuc l eus. The MM C underg o meioti c d i v i si o n r esulting f our haploid me g asp o r e s .

14. Gei t on o g a m y: P ollinat i on bet w een t w o fl o w ers of th e same plan t . P ollina t i o n b y pollina t ing agen t . Genetical l y similar t o th e au t o g a m y . X eno g a m y : T r ans f er of polle n g r ain s f r om th e anthe r t o the s t igma of d i f f e r ent plan t . I t is common l y called a s c r os s-pollinati o n. I t bring s genet i cal l y d i f f e r ent t y pe s o f polle n g r ains t o th e s t i g ma

15. Agents o f po l lina t io n :  Plant us e t w o abioti c agen t i.e. win d an d w a t er f or pollinati o n. On e bioti c agen t f or pollinati o n such a s animals. Majorit y of p l an t us e biot i c a gen t f or pollinati o n. F ew plan t us e abio t ic pollina t ing agen t .

16. Anemophi l y: P ol lin a t in g a g e n t is w i nd. Pla n t s p r od u ces e n orm o u s am o un t of po l le n w hen co m pa r ed t o th e n u m be r of o vules a v a i labl e f or po l lin a t i on t o c o m p e n sa t e th e unc e rt a i n t ie s of po l lin a t i on. Fl o w e r s wi t h w ell e xpose d sta mens. La r g e f e a ther y st igm a t o t r a p a ir -b o rne po l le n g r a i ns. Mos t w i n d po l lin a t ed fl o w er cont a in s sing l e o vule in one o v a r y a n d nume r ous fl o w er pac k ed in t o an inflo r esc e nc e e.g. corn co b . P ol l en g r a i n s a r e li g ht a n d no n - st i c k y .

17. H y d r ophilic: P ol lin a t ion b y abio t ic a g e n t li k e w a t e r . This t y p e of pollin a t i on is v e r y r a r e, abo u t 3 g e n e r a, m o st l y m o noc o t . V al l i s ne ri a , H y dri l la and Z o s t e r a a r e th e com m on ex ampl e f or H y d r op h i l y . Al l aquat i c p l a n t s a r e no t H y d r op h i l y . P ol l en g r a i n s r ele as e d in t o th e sur f ac e of w a t er a n d carr i ed t o th e st ig m a b y a ir c ur r e n t a s in V al l i s neri a . In sea g r as s th e fl o w e r s r ema i n e d subm e r ge d . P ol l en g r a i n s a r e l o n g , ri b bo n li k e a n d car r ie d pass i v e l y in side th e w a t er P ol l en g r a i n s a r e p r o t ec t ed f r om w et t i ng b y mucilag inous c o v erin g .

18. P olli n a t io n b y bioti c a gent: Majorit y of fl o w e r i n g plan t s us e a r a ng e of a n i ma l s as polli n ati n g age n ts. Among the a n i ma l , i n sect p a rticula r l y b e es a r e the d o mi n a n t b i o t ic age n ts f or polli n ation. Ins e ct polli n ati n g fl o w e r s a r e v e r y la r ge, c o lorful , f r ag r a n t a n d r i ch in n e c t a r . Sm a l l fl o w e r s p r es e n t in clust e r t o ma k e th e m c o nspicuous. Fl o w er polli n a t e d b y fli e s a n d b e etl e s s ec r e t e f oul o d ours. Nectar a n d poll e n g r ai n s a r e the usua l flo r al r e w a r ds f or i n sects. I n so m e speci e s flo r al r e w a r ds a r e in p r o v i ding s a f e pla c es t o l a y eggs: e . g. A morpho p hal l u s . A speci e s of mot h a n d Y ucc a plan t c a nno t c o mpl e t e th e ir l i f e c y cle w i thout each o t h e r . The mo t h deposits its eggs in the locul e of the o v ary a n d the fl o w er in t ur n get polli n a t e d b y t he mo t h. Ma n y i n sects m a y c o nsum e poll e n or n e c t ar w i thout br i n g about polli n ati o n . Suc h flo r al v i si t ors a r e r e f e r r ed as pol l en/nect a r r ob bers.

19. Ou t b r eed i ng D e vi c e s : Major i t y of th e fl o w e r in g plan t s p r od u ce hermaph r odi t e fl o w er a n d underg o au t o g a m y . Contin u o u s a u t o g a m y o r self - pollinatio n r esults i n inb r ee d in g d e p r essio n . Fl o w e r in g plan t s h a v e d e v eloped ma n y d e vice s t o a v oid self p ol lin a t ion a n d t o encou r a g e c r os s-po l lin a t i on. Such d e vice s a r e called Ou t b r ee d in g d e vi c es. P ol l e n r e l eas e d a n d stigma r e c e p t i vity i s n ot s y n ch r o n i zed. Spat i a l sepa r at i o n o f anth e r s an d st i gmas A n the r an d st i gma a r e pla c ed a t di f fe r e n t posit i o n s. S elf in c ompat i bil i t y . P r o d uctio n o f un is e x ua l fl o w e r s.

20. P ollen pisti l In t e r ac t io n : Al l the e v ents – f r om pollen depos i tion on the sti g m a until pol l en tube s en t er the o vule – a r e t o g ether r e f er r ed a s pol le n - pist i l i n t e r act i o n . P ollination does no t gu a r an t ee the t r ans f er of the ri g ht type of pol len g r ain t o the ri g ht typ e of sti g m a. The pi s ti l has the ability t o r eco g nize the pol l en w hether it is compatible or incompatible. I f it is ri g ht typ e the sti g m a all o w the pol l en t o g e rmina t e. I f it is w r ong typ e the sti g m a r ejects the pol l en, p r e v enting g e rmination. The ability of the pi s ti l t o r eco g nize the pol l en b y c ontinuous di alogu e m e di a t ed b y chemical li k e Bo r o n , I n osi t o l and suc r os e l e v el. F oll o win g comp a tible pol lin a tion , the pol l en g r ain p r oduce pol l en tub e th r ou g h one of the g e rm po r e.

21. Artifici a l h y bri d iza t ion: O n e of t he majo r app r oaches of c r op imp r o v eme n t p r og r amme. On l y desi r ed p o lle n g r a i n use d f or p o llina t ion. St i gm a is p r o t ec t ed f r om cont a min a t i on (f r om u n w a n t ed po l le n g r a i n). R em o v a l of a n ther s f r om th e fl o w er b ud be f o r e the an t her dehisces is called emasc u lation. Emasc u la t ed fl o w e r s c o v e r ed b y ba g g e n e r al l y mad e up of b u t t er pape r , t o p r e v e n t cont a min a t i on of i t s st igma w i t h u n w a n t ed po l len . This s t ep is c a lle d baggin g . I f th e f emale fl o w er is un i s ex ua l the r e is n o n e ed of emasculati on.

22. Doub le fertil i za t ion: Af t er en t ering one of the s yn e r gid s , the pol l en tub e r eleases t w o m a le g a m e t es in t o the cy t oplasm of the s yn e r gid s . S y n g a m y : one of the m a le g a m e t e fused wi th e g g cell, t o f orm a di p l oid z y go t e . T w o pola r nuc lei of cent r a l cell fused t o f orm a di p l oid se c o n dar y n u cle u s . T riple fus i on : The s econd m a le g a m e t e fused wi th the secondary nuc leus t o f orm a trip loid p r im ar y e n dos p erm n u cle u s. Since t w o typ e of fusion, s yn g a m y an d tri p le fusion t a k e p l ace in the embr y o sac the phenom en o n is t erm e d a s do u ble fert i lizatio n . The cent r a l cell af t er tri p le fusion become s p r im ary e n d o sp e rm c e l l a n d d e v elop e d in t o the e n d o sp e rm. The z y g o t e d e v eloped in t o a n e m br y o.

23. P O S T - FE R TILI Z A TI O N : S T R UC T URE AND E VEN T S E v ents of endo s p e rm an d embr y o d e v elo pmen t , matu r ati o n o f o v u l e in to s eed and o v ar y in to f r u i t , a r e col l ect i v e l y termed a s p os t - f e rtilizati o n e v en ts. E n d osp e rm: D e v elo pmen t of endos p erm ta k es plac e be f o r e t h e embr y o d e v elo pmen t . Primary endo sp e rm cell d i v i d e s r e p ea t e d l y t o f orm a tr i plo i d endos p erm. C ell s a r e fill ed wi t h r e s er v e f o o d ma t erial an d a r e use d f or t h e nu t riti o n of t h e d e v elo pin g embr y o. P E N unde r goe s succe s s i v e n uclear d i v i s io n to g i v e ri s e to f r ee n uclei. Th i s is c a l l ed f r e e - nuclea r en d os p e r m. Sub s equent l y cell w al l f orm ati o n ta k es plac e an d be come cellu la r endos p erm. The coco nu t w a t er is f r ee n uclear endos p erm an d th e w hite k ernel is th e cell u l ar endos p erm. Endos p erm m a y b e con sume d comple t e l y during embr y o d e v elo p e d or it m a y be con sume d during germ i nat i on of s ee d .

24. Emb r y o: Z y go t e f ormed an d pla c ed a t th e mic r o p y la r end of th e em b r y o sac. Z y go t e s t art s i t s d e v elop m e n t on l y af t er some amoun t of endo s per m f ormed. E m br y o d e v elop m e n t ta k es pla c e in f oll o wing s t age s : P r oembr y o Globula r stage H e ar t sha p ed Matu r ed em b r y o

25. Di c o t emb r y o: A t y pica l d i cot y ledonou s embr y o consi s t s of an embr y ona l axi s an d t w o c ot y led o n s . Emb r y onal axi s ab o v e th e cot y ledo n is th e epi c ot y ls. T er m inal par t of th e epicot y l s is t he pl u mul e (g iv es rise t o th e shoo t ). Emb r y onal axi s bel o w th e cot y ledo n is th e h ypo c ot y l . The t er m inal par t o f t he h ypocot y l is called th e r adicl e ( r o o t tip). The r o o t t i p is c o v e r ed b y th e r o o t ca p .

26. Mono c o t emb r y o: P osse s ses on l y one co t yledon In g ras s fami l y the cotyledon is called scutellum. Scutellum situ a ted t o w ard s one side of t he em b r y onal axi s . Radi c le an d the r oot cap enclosed b y a she a th called coleorhiz a. The po r tion of the em b r y onal axi s ab o v e l e v el of a tt a c hment of scu t ellum is called epicotyl s. Epicotyl has the shoot ape x or plu m ule enclosed b y h o ll o w foliar st r uc t u r e called coleoptil e. Se e d is the final p r odu c t of the s exual r ep r odu c tion. Seed consists of seed co a t, co t yledon an d a n em b r y o axi s .

27. Cot y ledo n s t o r es the r eser v e f ood m a t erial f or d e v elopment and g e rmination. Matu r ed seed wi thout endosperm called n o n - alb um i n o u s . (G r ound nut) A p a rt of the endosperm r et a in e d in matu r ed se e d is A lbumino u s. R e m ain a nt s of nucel l u s in the m a tu r ed seed is cal led pe r isperm . E.g . black peep e r , be e t . The w al l of the o v ary d e v elops in t o the w al l of fruit called p e ricar p . F ruit d e v eloped f r om the o v ary is called tru e frui t . In app le, st r a w ber r y , cashe w , the thalamu s contribu t es in the fruit f ormation is called false frui t . F ruit d e v eloped wi thout f ertilization is called P arthe n ocarpic fruits.

28. A P OMI X IS AND P O L YEMB R Y ON Y . Apomix i s is v e r y co m m o n in As te r ac e a e a n d g r ass e s. Se e ds a r e p r od u ced w i thou t f e rt i lization. Apo m ixis is a t y p e of as e x ua l r ep r od u ction w hich mimic s th e s e x ua l r ep r od u cti on. Dipl o id eg g cell is f ormed w i thou t me i osis a n d d e v elops in t o se e d w i thou t f e rt i liza t i o n . In C i tru s and Man g o th e nucel l a r cells st ar t s d i vid i ng, p r otrude in t o th e e m b r y o sac a n d d e v elop in t o embr y o. O v ul e h a vin g m o r e t han one embr y o is t e r med as po l y emb r y o n y . H y bri d plant s a r e d e v eloped b y apo m ixis t o m a i n t a i n th e g e n e t i c ide n t i t y .

29. Thankin g y ou