Sexual Reproduction in Flowering Plants: Class 12 Biology Chapter 1 Hinglish mein

February mein kisi mango orchard se guzro to har branch par chhote-chhote flowers ka guchha dikhta hai. May tak inmein se zyaadatar gir jaate hain, aur jo thode bache rehte hain woh fruit ban kar latakte hain, har ek ke andar ek hi seed. Us flower aur us seed ke beech events ka ek dhyaan se set kiya hua sequence hai: flowering plant ki sexual life.

Individual plants mar jaate hain, lekin ek species tab tak bachi rehti hai jab tak uske members offspring chhodte rehte hain. Asexually apni copy banakar plant tezi se phail sakta hai, lekin sirf sexual reproduction hi genes ko reshuffle karta hai, isliye har generation mein aise combinations aate hain jo pehle kabhi try nahi hue. Yahi variety nayi diseases aur badalte climate se nipatne ka raw material hai. Yeh chapter angiosperms mein sexual reproduction ko follow karta hai, pehle floral bud se lekar us seed tak jo ugne se pehle saalon intezaar kar sakta hai.

1.1 Flower – Angiosperms ka ek Fascinating Organ

Poore India mein flowers woh baat keh dete hain jo shabd nahi keh paate: Diwali par darwaze ke upar marigold ki ladiyan, choti mein gunthi jasmine, mandir mein lotus, funeral par white chrysanthemums. Bechne ke liye flowers aur ornamental plants ugana apne aap mein ek farming business hai, floriculture; marigold, rose, tuberose aur chrysanthemum un flowers mein se hain jo India commercially ugata hai.

Ek botanist ko flower mein colour aur khushboo se zyaada dikhta hai. Flower ek chhota shoot hai jiski leaves thalamus par chaar whorls mein reshape ho gayi hain Fig. 1.1. Bahar ke do whorls, sepals (calyx) aur petals (corolla), bud ko protect karte hain aur uska advertisement karte hain. Andar ke do reproduction ka kaam karte hain: stamens (androecium) male whorl banate hain aur pistils (gynoecium) female whorl.

To asal mein kaun se do parts sexual reproduction ki units banate hain? Pollen grains, jo male gametes le kar chalte hain, anthers ke andar develop hote hain. Embryo sac, jismein egg hota hai, ovary ke har ovule ke andar develop hota hai. Baaki chapter in do structures ko tab tak follow karta hai jab tak inke gametes mil nahi jaate.

1.2 Pre-fertilisation: Structures aur Events

Pre-fertilisation mein woh sab aata hai jo gametes ke fuse hone se pehle hona zaroori hai: male aur female gametophytes banana, phir unhe ek saath laana. Iski shuruaat ek switch se hoti hai. Koi bhi bud dikhne se bahut pehle, day length aur temperature jaise cues, hormones ke zariye, shoot tip ko leaves banane se hata kar floral primordium banane par laga dete hain. Woh primordium buds ke ek cluster mein badhta hai, aur har bud ke andar androecium aur gynoecium bante hain.

1.2.1 Stamen, Microsporangium aur Pollen Grain

Flower se ek stamen kheecho to tumhare haath mein do parts hote hain: ek patla stalk, filament, aur uske tip par anther, jo aam taur par two-lobed hota hai, jahan pollen banta hai. Filament thalamus se nikal sakta hai ya, brinjal aur datura mein, seedhe petals se (aise stamens epipetalous kehlate hain). Flowers mein stamens ki ginti aur unki lambai mein bahut farak hota hai. Mustard mein chhe hote hain, chaar lambe aur do chhote, jabki china rose mein darjanon hote hain jinke filaments style ke chaaron taraf ek tube mein fuse ho jaate hain.

Anther ko end-on dekho to usmein do lobes hote hain. Har lobe mein do microsporangia hote hain, isliye ek typical anther mein chaar hote hain Fig. 1.2. Botanists ise ek line mein kehte hain: bilobed, dithecous aur tetrasporangiate.11Alag-alag books ise alag tarah se kehti hain: kuch har lobe ko theca kehti hain, kuch sacs ke har pair ko. Ginti kabhi nahi badalti: do lobes, chaar microsporangia. Aksar anther ke dono halves ke beech neeche tak ek groove chalti hai. Sterile tissue ki ek patti, connective, lobes ko jodti hai aur filament se upar ek vascular strand le jaati hai.

Cross-section mein young anther lagbhag square hota hai, har corner par ek microsporangium. Har sac anther ki poori length mein chalta hai, aur maturity par yahi chaar pollen sacs hote hain.

Microsporangium ka structure

Cross-section mein microsporangium lagbhag circular hota hai. Bahar se andar ki taraf, iski wall mein chaar tarah ki layers hoti hain: epidermis, endothecium, kuch middle layers aur, sabse andar, tapetum. Sac ko protect karna aur anther pakne par use kholna pehli teen layers ka kaam hai. Endothecium cells mein thickening ki strips hoti hain; jab anther sookhta hai to yeh unevenly sikudti hain aur wall ko ek kamzor line par phaad deti hain, is process ko dehiscence kehte hain.

Tapetum nursery layer hai. Iske cells mein aksar do ya zyaada nuclei hote hain, kyunki nucleus mitosis se divide ho sakta hai bina uske baad cell ke divide hue. Tapetal cells develop hote pollen ko food dete hain, ek enzyme release karte hain jo young microspores ko ek doosre se alag karta hai, aur pollen ki sakht outer wall ka raw material secrete karte hain. Pollen ban jaane ke baad tapetum toot jaata hai.

Young microsporangium ke centre mein ek jaise cells ka ek compact block hota hai, sporogenous tissue. Inmein se har cell pollen mother cell ban sakta hai.

Microsporogenesis

Pollen mother cell (PMC) diploid hota hai. Yeh meiosis se chaar haploid cells mein divide hota hai jo kuch der ek saath microspore tetrad ke roop mein rehte hain Fig. 1.3. PMC se microspores tak ke is meiotic route ko botanists microsporogenesis kehte hain. Kyunki meiosis chromosome number ko aadha kar deta hai, tetrad ka har cell haploid (n) hota hai. Pakte anther ke sookhne se tetrads dheele padte hain, aur har free microspore mature hokar pollen grain banta hai; ek akele sac mein hazaaron ho sakte hain.

Pollen grain

Har pollen grain ek male gametophyte hai, ek chhota sa haploid structure jo male gametes banayega aur pahunchayega. Ek pakke lily ya marigold anther ko slide par paani ki boond ke upar thapthapao aur microscope mein dekho: grains size, shape, colour aur surface pattern mein alag hote hain. Scanning electron microscopes mein yeh kaanton wali balls, jaali wale spheres ya grooved ovals jaise dikhte hain, aur yeh patterns itne khaas hote hain ki ek grain se uske plant ki pehchaan ho sakti hai.

Zyaadatar grains lagbhag 25–50 µm ke spheres hote hain, insaan ke baal ki motai se bhi chhote, aur ek two-layered wall mein lipte hote hain. Bahari layer, exine, sabse mazboot part hai. Yeh sporopollenin se bani hai, ek aisa polymer jo itna tikaau hai ki heat, strong acid ya strong alkali bhi use kuch nahi kar paate, aur koi aisa enzyme pata nahi hai jo use digest kar sake. Scientists is mazbooti ka faayda uthate hain: pollen rocks mein fossils ke roop mein bacha rehta hai, aur jheel ki mitti mein phanse grains batate hain ki hazaaron saal pehle aas-paas kaun se plants ugte the.

Exine mein gaps hote hain. Ek ya zyaada patli jagahon par, jinhe germ pores kehte hain, sporopollenin nahi hota, aur baad mein inmein se kisi ek se pollen tube bahar niklegi. Exine ke neeche cellulose aur pectin ki ek bina tooti layer, intine, grain ko andar se line karti hai, aur andar ke cytoplasm ki apni plasma membrane hoti hai.

Andar, ek pakke grain mein do bahut alag size ke cells hote hain. Dense cytoplasm wala ek chhota, spindle-shaped generative cell ek kaafi bade vegetative cell ke andar latka hota hai, jismein food reserves aur ek bada, irregular nucleus hota hai. Generative cell gametes banayega; vegetative cell tube banayega. Species mein timing alag hoti hai. Zyaadatar (60 % se zyaada) pollen ko isi two-celled state mein release karti hain, jabki baaki pehle generative cell ko mitosis se divide hone deti hain aur do male gametes wale three-celled grains shed karti hain.

Release hone ke baad pollen grain ko zinda rehte hue hi stigma tak pahunchna hota hai. Yeh kitni der viable rehta hai, yeh species aur temperature aur humidity par depend karta hai. Rice aur wheat ka pollen lagbhag aadhe ghante mein mar jaata hai, jabki rose, pea aur potato families ke kuch members ka pollen mahinon tak viable rehta hai.

1.2.2 Pistil, Megasporangium (ovule) aur Embryo sac

Gynoecium ek single carpel ka ho sakta hai (monocarpellary, jaise pea mein) ya kai carpels ka (multicarpellary). Kai carpels fuse hokar ek compound pistil bana sakte hain (syncarpous, jaise lady's finger aur tomato mein) ya alag reh sakte hain (apocarpous, jaise lotus aur custard apple mein) Fig. 1.4.

Pollen grain ke saath andar chalo to pistil ke teen parts kram se milte hain. Pehle aata hai stigma, ek chipchipi ya feathery receiving surface. Phir style, ek gardan jo chhoti ya bahut lambi ho sakti hai. Aakhir mein ovary, phooli hui base. Ovary ek cavity ko gherti hai, locule, aur uski wall par tissue ki ek ridge, placenta, ovules ko rakhti hai. Ovary mein ek hi ovule ho sakta hai (maize, ya sunflower head ka har chhota floret) ya saikdon (brinjal, guava, tomato).

Ovule (megasporangium)

Ovule ko, jo flower ka megasporangium hai, ek parcel ki tarah socho. Iske core mein nucellus hai, food se bhare cells ka ek mass. Nucellus mein dabba hai embryo sac, yaani female gametophyte; normally har ovule mein ek hota hai, jo ek single megaspore se banta hai. Nucellus ke chaaron taraf ek ya do protective wrappings hoti hain, integuments, jo sirf ek patla entry channel chhodti hain, micropyle Fig. 1.5.

Yeh parcel ek stalk se placenta par latka hota hai, funicle, aur jahan stalk ovule body se milta hai woh point hilum hai. Micropyle ke ulte end ko, jahan integuments aur nucellus base par mil jaate hain, chalaza kehte hain. Zyaadatar angiosperm ovules anatropous hote hain: ovule body apne funicle par poori tarah palat jaati hai, isliye micropyle wapas hilum ki taraf point karta hai.

Megasporogenesis

Micropyle ke paas nucellus ka ek cell alag dikhta hai: yeh apne padosiyon se bada hai, iska cytoplasm dense hai aur nucleus bada hai. Yeh diploid megaspore mother cell (MMC) meiosis se chaar haploid megaspores mein divide hota hai, jo aam taur par ek row mein hote hain Fig. 1.6. MMC se megaspores banne ko megasporogenesis kehte hain.

MMC ko meiosis se hi divide kyun hona padta hai? Baad mein fertilisation do gametes ko fuse karke chromosome number double kar dega. Pehle use aadha karne se zygote apne parents jitne hi diploid number par rehta hai, aur meiosis ka crossing over genes ke naye combinations jodta hai.

Female gametophyte (embryo sac)

Zyaadatar flowering plants mein chaar megaspores mein se teen degenerate ho jaate hain, aur sirf ek, aam taur par chalaza ke sabse paas wala, functional megaspore ke roop mein bachta hai. Kyunki embryo sac isi single megaspore se banta hai, iske development ko monosporic kehte hain.

Iske baad mitosis ke teen rounds hote hain, 1 → 2 → 4 → 8 nuclei, aur inmein se kisi ke baad bhi cell wall nahi banti. Pehle round ke baad dono nuclei badhte sac ke ulte ends par chale jaate hain, aur har agla round dono ends par nuclei double kar deta hai. Aisa free-nuclear division young sac ko aath nuclei wala ek bada cell bana deta hai; uske baad hi walls banti hain.

Mature sac ko chalazal end se padho. Wahan teen antipodal cells ek group mein hote hain. Beech mein ek bada central cell hai jo ek ki jagah do nuclei rakhta hai, polar nuclei. Micropylar end par egg apparatus hai: ek egg cell jiske dono taraf do synergids hain, jinke micropylar tips par ungli jaisi wall ingrowths hoti hain, filiform apparatus, jo aati hui pollen tube ko raasta dikhane mein madad karti hain. Sabko jodo to sac mein sirf saat cells mein aath nuclei hain Table 1.2.

1.2.3 Pollination

Pollen grains aur embryo sacs alag-alag organs mein bante hain, aur na male gametes na egg khud se travel kar sakte hain. Inke beech ka pul hai pollination. Kyunki plant apna pollen khud nahi le ja sakta, woh bahar ke carriers par depend karta hai: wind, water ya animals.

Pollination ke prakaar

Pollination ka naam pollen ke source ke hisaab se rakha jaata hai Fig. 1.7. Autogamy mein pollen usi flower ke stigma par girta hai jisne use banaya. Open flower ke liye yeh jitna lagta hai usse mushkil hai: uske anthers aur stigma ek hi samay par ready hone chahiye aur itne paas hone chahiye ki chhoo sakein. Bahut se open flowers ek ya doosri shart mein fail ho jaate hain, isliye unmein complete autogamy rare hai.

Violets (Viola) aur dayflower (Commelina) ek hi plant par do tarah ke flowers banakar risk kam karte hain. Normal open, chasmogamous flowers ke saath woh cleistogamous flowers bhi banate hain jo zindagi bhar band rehte hain. Aise band bud ke andar anthers stigma ke saamne hi khulte hain, isliye pollination apne aap ho jaata hai, aur kyunki bahar se kuch andar nahi aa sakta, yeh hamesha autogamy hota hai. Faayda yeh hai ki bina pollinators wale season mein bhi seed pakka milta hai; keemat yeh hai ki woh saare seeds selfing se aate hain.

Geitonogamy mein pollen usi plant ke doosre flower par jaata hai. Ise cross-pollination ki tarah ek carrier chahiye, isliye bahar se yeh crossing jaisa dikhta hai. Lekin genetically yeh selfing hai, kyunki pollen aur egg ek hi individual se aate hain. Xenogamy mein pollen doosre plant ke flower se aata hai. Sirf xenogamy hi genetically alag pollen stigma tak laata hai, isliye sirf xenogamy hi naye gene combinations wale offspring banata hai.

Pollination ke agents

Zyaadatar flowering plants carriers ke roop mein animals ko 'hire' karte hain. Kuch hi plants wind par, ya kabhi-kabhi water par, bharosa karte hain, aur iski keemat pollen mein chukate hain. Jo carrier nishaana nahi laga sakta woh zyaadatar grains ko stigma se kahin door gira deta hai, isliye wind- aur water-pollinated plants har us ovule ke liye jise fertilise karna hai, bahut zyaada pollen shed karte hain.

Do non-living carriers mein wind zyaada common hai. Iske liye design kiye gaye flower ko imagine karo. Use showy petals ki zaroorat nahi. Uska stigma bada aur aksar feathery hona chahiye, taaki hawa se grains ko kangi ki tarah nikaal sake, aur uske stamens khule mein latakne chahiye jahan hawa unhe hila sake. Pollen halka, sookha aur non-sticky hona chahiye. Kyunki har grain ka nishaane par lagna mushkil hai, aise flowers mein aam taur par ek-ek ovule hota hai aur woh darjanon ki sankhya mein ek inflorescence mein bhare hote hain. Wheat, rice, sugarcane aur bamboo jaisi grasses is description mein fit hoti hain. Young maize cob par silky dhaagon ka guchha lambe styles aur stigmas ka bundle hai, har future kernel ke liye ek.

Water pollination do tarah ka hota hai Fig. 1.8. Surface par: Vallisneria mein, jo ponds aur dheemi nadiyon ki ek eelgrass hai, female flower ek lambe, ghumaavdaar stalk par surface par tika rehta hai. Iske male flowers paani ke neeche toot kar alag hote hain, upar aate hain aur surface film par tab tak bahte hain jab tak kuch usse takra na jaayein. Surface ke neeche: Zostera jaisi seagrasses mein flowers paani mein doobe rehte hain aur lamba, dhaage jaisa pollen chhodte hain jise current stigmas tak bahaa le jaata hai. Dono tarah se pollen ko paani se bheegna nahi chahiye, aur aisi zyaadatar species mein mucilage ki ek chikni coat use protect karti hai.

Water pollination unusual hai: sirf lagbhag 30 genera ise use karte hain, zyaadatar monocots, jinmein Vallisneria ke saath Hydrilla bhi hai. Sirf paani mein rehna kaafi nahi hai. Lotus aur water hyacinth apne flowers ko surface ke upar rakhte hain aur zyaadatar land plants ki tarah insects se pollinate hote hain. Algae, mosses aur ferns se compare karo, jinke male gametes ko egg tak tair kar jaana padta hai; maana jaata hai ki paani ki yeh zaroorat kuch mosses aur ferns ke ugne ki jagah ko limit karti hai.

Wind ya water se pollinate hone wale flowers aam taur par chhote aur pheeke hote hain aur nectar nahi banate. Unhe kisi animal ko attract nahi karna hota, isliye colour, scent ya nectar par energy kharch karna bekaar hota.

Zyaadatar kaam animals karte hain, aur insects, sabse zyaada bees, sabse aage hain. Butterflies aur moths lambi jeebh se nectar peete hain; flies, beetles, wasps aur yahan tak ki ants bhi pollen le jaate hain. Vertebrates mein, sunbirds coral-tree aur silk-cotton ke flowers par khaate hain, bats baobab jaise raat mein khulne wale bade flowers par jaate hain, aur kuch species mein lemurs, pedon par rehne wale rodents ya geckos yeh kaam karte hain. Aksar flower ki shape, colour aur timing ek tarah ke visitor ko baaki sabse kahin zyaada suit karti hai.

Animal-pollinated flower ek simple deal chalata hai: advertise karo, reward do, aur pollen mein fee lo. Advertisement colour, scent ya dono hota hai, aam taur par bade flowers par. Chhote flowers milkar showy heads banate hain, jaise sunflower aur marigold mein, aur jo flowers flies ya beetles chahte hain woh sadte maans ya gobar ki badboo se advertise karte hain. Reward aam taur par nectar ya pollen hota hai. Fee tab li jaati hai jab visitor kha raha hota hai: woh anthers se ragad kar nikalta hai aur chipchipe pollen se dhaka hua jaata hai, jismein se kuch woh agle chhue stigma par poonch deta hai.

Outbreeding devices

Inbreeding ki ek keemat hoti hai. Generation dar generation selfing harmful recessive alleles ko saath le aati hai aur kamzor, kam fertile plants banati hai; is girawat ko inbreeding depression kehte hain. Phir bhi zyaadatar flowering plants mein anthers aur stigma ek hi flower mein hote hain, isliye apna pollen hamesha paas hi hota hai. Evolution ne iska jawab kai outbreeding devices se diya hai.

• Timing. Pollen usi flower ke stigma ke receptive hone se pehle shed ho jaata hai (protandry), ya stigma pollen shed hone se pehle receptive ho jaata hai (protogyny). Isse autogamy rukti hai.
• Position. Anthers aur stigma aise rakhe hote hain ki flower ka apna pollen uske stigma tak kam hi pahunchta hai (herkogamy). Isse bhi autogamy rukti hai.
• Self-incompatibility. Ek genetic recognition system pistil ko same plant ka pollen reject karne deta hai, chahe woh same flower se ho ya bagal wale flower se, germination ya tube growth ko block karke. Tab na autogamy se seed milta hai na geitonogamy se.
• Unisexual flowers. Jab male aur female flowers ek hi plant par hote hain (monoecious, jaise maize, castor, cucumber aur coconut mein), to autogamy impossible hai lekin geitonogamy nahi. Jab male aur female flowers alag plants par hote hain (dioecious, jaise papaya, date palm aur spinach mein), to autogamy aur geitonogamy dono ruk jaate hain.

Pollen–pistil interaction

Stigma ek security desk ki tarah kaam karta hai. Har tarah ke grains aate hain: sahi species ke, doosri species ke aur, self-incompatible plants mein, plant ke apne. Har grain ko pollen aur pistil ke beech molecules ke exchange se check kiya jaata hai, aur sirf compatible pollen ko germinate hone aur tube banane ke liye aage jaane diya jaata hai. Incompatible pollen ko mana kar diya jaata hai, ya to desk par hi, jahan woh stigma par germinate nahi kar paata, ya aur andar, jahan uski tube style mein ruk jaati hai.

Botanists ne is exchange ke pollen aur pistil molecules mein se sirf kuch ko hi pehchaana hai, aur kaam abhi jaari hai.

Accept kiye gaye pollen ke liye ek safar shuru hota hai Fig. 1.10.

1. Germination. Grain stigma se paani absorb karta hai, aur ek pollen tube ek germ pore se bahar ubharti hai; grain ka cytoplasm aur nuclei usmein chale jaate hain.
2. Growth. Tube ka tip stigma aur style ke cells ke beech zor lagakar neeche badhta hai, kabhi-kabhi kai centimetres tak, jab tak woh ovary mein na pahunch jaaye. Two-celled shed hone wale pollen mein generative cell raaste mein divide hokar do male gametes banata hai; three-celled pollen unhe shuru se hi le kar chalta hai.
3. Entry. Zyaadatar tubes ovule mein uske micropyle se ghusti hain aur phir ek synergid mein push karti hain; is aakhri hisse mein filiform apparatus unhe raasta dikhata hai.

Stigma par pollen ke pahunchne se lekar tube ke ovule mein ghusne tak sab kuch biologists ek naam ke neeche rakhte hain, pollen–pistil interaction. Ise samajhna breeders ki madad karta hai: ise manipulate karke woh kabhi-kabhi un crosses se bhi hybrids paa lete hain jinhe pistil normally reject kar deta.

Artificial hybridisation

Breeders aksar do varieties ko, kabhi-kabhi do species ya genera ko bhi, cross karte hain taaki useful traits ek plant mein aa jaayein. Yeh artificial hybridisation tabhi kaam karta hai jab stigma ko sirf chuna hua pollen mile aur kuch nahi Fig. 1.11. Maan lo ek breeder high-yielding tomato (female parent) ko ek aise wild relative (male parent) se cross karna chahta hai jo leaf virus ko resist karta hai. Tomato ke flowers bisexual hote hain aur khud ko pollinate kar sakte hain, isliye breeder chaar steps mein kaam karta hai.

1. Emasculate karo. Jab chuna hua flower abhi bud hi ho, kisi bhi anther ke pollen release karne se pehle, fine forceps se uske saare anthers nikaal do. Ise emasculation kehte hain.
2. Bag karo. Emasculated bud par butter-paper ka ek chhota bag chadhao aur baandh do, taaki insects ya wind se aaya koi pollen stigma tak na pahunch sake. Ise bagging kehte hain.
3. Pollinate karo. Jab stigma receptive ho jaaye, bag kholo aur wild parent ke anthers se ikattha kiya pollen stigma par chhidko.
4. Phir se bag aur label karo. Bag dobara band karo, flower par date aur dono parents ka tag lagao, aur fruit ko develop hone do; uske seeds hi hybrids hain.

Unisexual flowers wale female parent, jaise bottle gourd, ko emasculation ki zaroorat nahi, kyunki uske female flowers mein anthers hote hi nahi. Female bud ko khulne se pehle bag kiya jaata hai, stigma ready hone par pollinate kiya jaata hai aur phir se bag kiya jaata hai.

1.3 Double Fertilisation

Pollen tube do male gametes laati hai, aur flowering plant dono ko use karta hai, jo koi aur plant group nahi karta. Jaise hi tube ka tip synergid ke andar phatta hai, gametes release hote hain aur do alag targets ki taraf jaate hain Fig. 1.12.

• Gamete 1 → egg. Iska nucleus egg nucleus se judta hai (n + n). Gametes ka yeh fusion, syngamy, diploid zygote banata hai, jo embryo ka pehla cell hai.
• Gamete 2 → central cell. Iska nucleus dono polar nuclei se judta hai (n + n + n). Teen nuclei judte hain, isliye naam hai triple fusion; result triploid primary endosperm nucleus (PEN) hai, aur ise rakhne wala central cell ab primary endosperm cell (PEC) hai.

Kyunki ek hi embryo sac mein dono events hote hain, poore process ko double fertilisation kehte hain. Yahan se dono products ke raaste alag ho jaate hain: zygote embryo banega, jabki PEC endosperm banata hai jo use khana dega. Synergids aur antipodals, apna kaam khatam karke, degenerate ho jaate hain.

1.4 Post-fertilisation: Structures aur Events

Double fertilisation khatam hote hi chaar changes saath-saath chalte hain: endosperm develop hota hai, embryo develop hota hai, har ovule mature hokar seed banta hai aur ovary mature hokar fruit banti hai. Inhe milakar post-fertilisation events kehte hain.

1.4.1 Endosperm

Endosperm pehle kyun aata hai? Zyaadatar zygotes tab tak divide nahi hote jab tak kuch endosperm ban na jaaye, isliye embryo food supply ke bina kabhi badhna shuru nahi karta.

Zyaadatar plants mein endosperm do phases mein banta hai Fig. 1.13. Pehle mein PEN baar-baar divide hota hai lekin walls nahi banti, isliye central cell free nuclei se bhar jaata hai: yeh free-nuclear endosperm hai. Doosre mein nuclei ke chaaron taraf walls banti hain, edge se shuru hokar andar ki taraf, aur tissue cellular endosperm ban jaata hai. Walls aane se pehle kitne free nuclei bante hain, ismein species bahut alag hoti hain. Dono tarah se, taiyaar endosperm triploid hota hai aur uske cells food se bhare hote hain.

Coconut dono stages ek saath dikhata hai. Tender green coconut ka meetha paani free-nuclear endosperm hai, free nuclei se bhara hua. Jaise-jaise nut mature hota hai, bahar se andar ki taraf nuclei ke chaaron taraf walls banti hain, aur white kernel paani ki keemat par mota hota jaata hai. Jo kernel tum chutney ke liye kaddukas karte ho woh cellular endosperm hai.

Phir seeds is baat mein alag hote hain ki woh kitna endosperm bachate hain. Gram ya groundnut ka embryo seed pakne se pehle hi saara endosperm absorb kar leta hai aur food ko apne cotyledons mein store karta hai. Castor, coconut aur cereals germination tak bada endosperm rakhte hain, jab seedling usse khana leta hai.

1.4.2 Embryo

Bean aur wheat ka daana bilkul alag dikhte hain, phir bhi unke embryos ek hi tarah shuru hote hain; farak baad mein embryogeny, yaani embryo ke development, mein aate hain Fig. 1.14. Growth sac ke micropylar end par shuru hoti hai, jahan zygote hota hai. Zygote divide hokar ek proembryo banata hai jo cells ki ek chhoti chain, suspensor, par tika hota hai, jo use endosperm mein dhakelti hai. Proembryo cells ki ek ball banta hai (globular stage), phir do lobes wala heart-shaped embryo jiske lobes pehle cotyledons hain, aur aakhir mein ek mature embryo.

Cotyledons ko landmark ki tarah use karo Fig. 1.15. Dicot embryo ke do cotyledons uske central embryonal axis se ek level par judte hain, cotyledonary node par. Us level ke upar axis ka hissa epicotyl hai (epi, upar), jiske top par plumule hai, yaani future shoot. Neeche ka hissa hypocotyl hai (hypo, neeche), jo radicle par khatam hota hai, yaani future root, jiske tip ko ek root cap bachata hai.

Monocots mein ek cotyledon hota hai, aur grass embryo mein do protective sheaths aur hoti hain. Wheat, rice ya maize mein single cotyledon scutellum hai, ek dhaal jo axis ki ek side par hoti hai aur endosperm se sati hoti hai, jisse woh germination ke dauraan food absorb karti hai. Axis ka root end (radicle aur root cap) coleorrhiza mein lipta hota hai. Shoot end, yaani scutellum ke upar ka epicotyl apne shoot apex aur pehle leaf primordia ke saath, ek khokhle, patti jaise coleoptile se dhaka hota hai. Yahi woh nukeela sheath hai jo wheat ke germinate hone par sabse pehle upar aata dikhta hai.

1.4.3 Seed

Ab tak sab kuch ek product par khatam hota hai, seed: ek paka hua, fertilised ovule, jo fruit ke andar pack hota hai. Koi bhi seed kholo to wahi teen parts milte hain: ek protective seed coat, ek embryonal axis, aur ek ya do cotyledons, jo beans aur gram mein mote, phoole hue food stores hote hain.

Figure ek young seed ko teen raaston par follow karta hai Fig. 1.16. Agar pakne se pehle embryo endosperm ka aakhri cell tak absorb kar leta hai, to seed non-albuminous (exalbuminous) hota hai: pea, gram aur groundnut iske examples hain. Agar kuch endosperm bach jaata hai, to seed albuminous hota hai: castor, coconut aur wheat, maize aur barley jaise cereal grains. Aur kuch seeds mein ek teesra store bhi bachta hai, bacha hua nucellus jise perisperm kehte hain, jaise black pepper aur beet mein.

Do aur changes seed ko poora karte hain. Iske coats sakht ho jaate hain: outer integument testa banta hai aur inner wala, jahan ho, tegmen, jabki purana micropyle ek pore ke roop mein bacha rehta hai jo baad mein paani aur oxygen andar aane deta hai. Aur yeh sookhta hai: paani seed ke mass ka lagbhag 10–15 % reh jaata hai, aur embryo ka metabolism lagbhag ruk sa jaata hai. Phir pakka seed ya to dormancy mein aaraam karta hai ya, moisture, oxygen aur sahi temperature milne par, germinate karta hai.

Isi beech seeds ke chaaron taraf ki ovary fruit ban rahi hoti hai, aur uski wall fruit wall, yaani pericarp. Tomato, grape ya papaya mein pericarp naram aur rasila ho jaata hai; pea pod, cotton boll ya sunflower ke 'seed' (jo asal mein ek sookha one-seeded fruit hai) mein yeh sookh jaata hai. Dono tarah ke fruits mein hooks, wings, gooda ya springs ho sakte hain jo seeds ko bikherne mein madad karte hain. Aur kyunki har seed ek fertilised ovule hai, fruit mein kabhi bhi uski ovary ke ovules se zyaada seeds nahi ho sakte.

Apple ke andar dekho to tum ek false fruit dekh rahe ho: kurkura gooda zyaadatar phoola hua thalamus hai, aur seeds ke chaaron taraf ka sirf kaagazi core ovary se aaya hai. Strawberry bhi aisi hi hai, uska laal gooda thalamus hai jis par chhote-chhote true fruits lage hain. Iske ulat, zyaadatar plants mein baaki floral parts murjha jaate hain aur fruit sirf ovary se banta hai: ek true fruit.

Banana mein kehne laayak seeds nahi hote kyunki uska fruit fertilisation ke bina badhta hai, is condition ko parthenocarpy kehte hain. Growers kuch crops mein, jaise tomato mein, flowers par auxins jaise growth regulators spray karke yahi cheez karwa sakte hain; isse bane fruits seedless hote hain.

Seeds itne successful kyun rahe hain? Seed ek travel case hai: sakht coat wala aur sookha, yeh wind, water ya animals ke saath nayi zameen tak le jaaye jaane ko jhel leta hai, isliye species naye areas mein phail sakti hai. Yeh ek packed lunch hai: iske reserves seedling ko tab tak chalate hain jab tak uski pehli leaves photosynthesis na karne lagein. Yeh ek genetic reshuffle hai: har seed mein parents ke genes ka naya mix hota hai. Aur yeh khade paani par depend nahi karta, kyunki pollination aur fertilisation ko paani nahi chahiye, isliye sookhi jagahon mein bhi seeds bharose se bante hain.

Seeds hi farming ka aadhaar bhi hain. Sookha, dormant seed store kiya ja sakta hai, isliye ek harvest logon ko saal bhar khilata hai aur uska kuch hissa agle season mein bone ke liye rakha jaata hai. Farmers jaante hain ki jab yeh fail hota hai to kya hota hai: bemausam baarish ke baad grain plant par hi sprout ho sakta hai, aur sprout hua grain na store ho sakta hai na boya ja sakta hai.

Seeds ki umr kuch mahinon se lekar sadiyon tak hoti hai, yeh species par aur is par depend karta hai ki seeds ko kitna sookha aur thanda rakha gaya hai; zyaadatar kuch saal chalte hain.

1.5 Apomixis aur Polyembryony

Dandelion ka seed apni mother jaisa hi plant ban sakta hai, bina kabhi koi pollen flower tak pahunche. Sunflower family (Asteraceae) ke kuch members, jinmein dandelion bhi hai, aur kuch grasses bina kisi fertilisation ke seeds banate hain. Is process ko apomixis kehte hain: sexual reproduction ke bhes mein asexual reproduction, kyunki end product phir bhi seed hi hai. Iski tulna parthenocarpy se karo, jo fertilisation skip karke seedless fruit banati hai.

Plants is result tak alag-alag raaston se pahunchte hain. Ek raasta meiosis ko skip karta hai: diploid nuclei wala embryo sac banta hai, aur uska egg bina fertilise hue embryo ban jaata hai. Ek zyaada common raasta, jo bahut si citrus aur mango varieties mein dikhta hai, nucellus ko use karta hai: embryo sac ke paas ke cells divide hona shuru karte hain, usmein ubhar aate hain aur apne khud ke embryos ban jaate hain Fig. 1.18.

Jab ek seed mein do ya zyaada embryos hote hain, to hum ise polyembryony kehte hain. Extra nucellar embryos mother ke apne diploid cells se bante hain, bina meiosis aur bina fusion ke. Isliye woh genetically mother plant aur ek doosre jaise hi hote hain: woh clones hain. Sirf zygotic embryo, agar bacha rahe, pollen parent ke genes le kar chalta hai.

Apomixis plant breeders ko itna excite kyun karta hai? Hybrid cotton ugane wali ek farmer ke baare mein socho. Hybrid ki high yield uske do parents ke genes ke ek khaas combination par depend karti hai, aur woh combination sirf pehli generation mein hi tikta hai. Uski fasal se bachaya gaya seed segregate hote, ek jaise na dikhne wale plants ka khet dega, isliye use har season mehngi hand-crossing se bana taaza hybrid seed khareedna padta hai.

Agar uska hybrid apomictic hota, to uske seeds hybrid mother plant ke clones hote, bina segregation ke wahi gene combination le kar. Tab woh unhe saal dar saal bacha kar dobara bo sakti thi. Isiliye duniya bhar ki laboratories apomixis ki genetics samajh rahi hain aur apomixis genes ko hybrid crop varieties mein daalne ki koshish kar rahi hain.