Plant Growth and Development | NEET Hinglish Notes | Class 11 Biology

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1. Introduction

Kya aapne kabhi socha hai ki roots, stems, leaves, flowers, fruits, aur seeds jaise structures plant me kaise develop hote hain aur woh bhi ek specific order me? Ab tak, aapko shayad seed, seedling, plantlet, aur mature plant jaise words pata hi honge. Aapne notice kiya hoga ki trees waqt ke sath height aur thickness me grow karte rehte hain. Lekin, chahe tree continue kare grow karna, uske leaves, flowers, aur fruits size me limited rehte hain. Aur ye specific time par appear hote hain aur girte bhi hain, aur kabhi-kabhi ye repeat bhi hota hai. Kya aapne kabhi socha ki plant pehle apne leaves aur stems (vegetative phase) kyun grow karta hai before ki wo flowers (flowering phase) produce kare?

Har part of plant different kinds of tissues se bana hota hai, aur ye important hai poochhna ki kya structure of a cell, tissue, ya organ ka connection uske function se hai jo wo perform karta hai. Kya possible hai ki unka structure aur function change ho sakta hai?

Plant ke saare cells originally ek single cell se aate hain jise zygote kehte hain. Toh, kaise aur kyun plant ke different cells alag dikhte aur behave karte hain, jabki wo sab same starting cell se aaye hain?

Word development me do main processes include hote hain: growth aur differentiation. Abhi ke liye, ye jaana important hai ki ek plant ka development zygote (fertilised egg) se ek bahut hi specific aur well-organised way me hota hai. Jaise-jaise plant develop karta hai, wo ek complex body form karta hai jo roots, leaves, branches, flowers, fruits, aur seeds ko janam deta hai. Eventually, plant apni life complete karta hai aur mar jaata hai.

Plant growth ka sabse pehla step hai seed germination. Ek seed tab germinate karta hai jab environment uske grow karne ke liye right conditions provide karta hai. Agar ye favourable conditions missing ho, toh seed grow nahi karta aur ek resting stage me chala jaata hai jahan uski growth kuch time ke liye ruk jaati hai. Jab right conditions wapas aati hain, seed apni metabolic activities phir se start karta hai aur grow karna shuru karta hai.

Is chapter me, aap ye bhi seekhenge ki kaunse various factors plant’s developmental processes ko affect aur control karte hain. Ye factors do types ke hote hain — kuch intrinsic (internal) hote hain plant ke liye, aur kuch extrinsic (external) hote hain, iska matlab ye hai ki ye outside environment se aate hain.

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2. Progressive and Irreversible Increase in Plant Body Dimensions

Growth ko consider kiya jaata hai as one of the most important aur easily noticeable features of all living organisms. Lekin growth exactly kya hai? Isko describe kiya jaa sakta hai as a permanent aur irreversible increase in the size of an organ, kisi bhi part, ya even ek single cell. Iska matlab hai ki ek baar kuch grow kar jaaye, toh wo apne original size me apne aap nahi jaa sakta.

Usually, growth hota hai metabolic processes ke saath, jo dono anabolic (building up) aur catabolic (breaking down) reactions include karte hain. Ye processes energy use karte hain growth me help karne ke liye. For example, jab ek leaf expand karta hai, ye growth ka form hai. Lekin ab kuch alag sochiye: agar ek piece of wood water me dalne par swell ho jaata hai, kya ise growth kaha jaa sakta hai? Nahi, kyunki ye swelling temporary hai aur original size me wapas aa sakta hai, toh ye definition of permanent growth me fit nahi hota.

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2.1 Unlimited and Continuous Expansion in Plants

• Plant growth special hai kyunki, animals ke unlike, plants apni entire life me without limits grow kar sakte hain. Ye continuous growth ability aati hai plant body ke special areas se jise meristems kehte hain. Meristems me jo cells hote hain unke paas unique ability hoti hai ki wo again and again divide kar sakte hain, aur apne aap ko maintain bhi kar sakte hain.
• Lekin jo new cells meristem se produce hote hain, wo eventually divide karna stop kar dete hain, aur instead, wo plant body ke different parts me develop karte hain. Is type ka growth, jahan new cells constantly meristem activity se add hote rehte hain, ise open form of growth kehte hain.
• Lekin ek moment ke liye sochiye — agar meristem divide karna stop kar de ? Us case me plant ki growth kya hoti ? Kya aise stoppage kabhi ho sakta hai ?
• Aapki earlier classes me, aapne already root apical meristem aur shoot apical meristem ke baare me padha hai. Ye meristems mainly responsible hote hain plants ke primary growth ke liye. Ye help karte hain plant ko longer grow karne me along its main axis — matlab, root se shoot tak.
• Aap ye bhi jaante hain ki dicotyledonous plants aur gymnosperms me, kuch aur meristems later life me appear hote hain. Ye hote hain lateral meristems, aur main ones hain vascular cambium aur cork cambium. Ye lateral meristems responsible hote hain plant organs jaise stem aur root ki thickness (girth) increase karne ke liye jahan ye active hote hain. Is type ka thickening of plant body ko secondary growth kehte hain.

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2.2 Increase in Plant Size Can Be Quantified

Cellular level par, growth mainly hota hai because of increase in the amount of protoplasm in the cell. Lekin, protoplasm ko directly measure karna kaafi hard hai, isliye instead, hum dusre cheezein measure karte hain jo usually proportional hoti hain protoplasm ke amount ke.

Isliye growth ko measure kiya jaata hai using different parameters. Kuch examples hain: increase in fresh weight, dry weight, length, area, volume, aur number of cells.

Aapko shayad surprise ho ki ek single maize root ka apical meristem har ghante me 17,500 se zyada new cells produce kar sakta hai. Dusri taraf, ek watermelon ka cell apni size me 3,50,000 times tak increase kar sakta hai.

Pehle example me, growth dikhaya jaata hai by increase in cell number, jabki dusre example me, ye dikhaya jaata hai by increase in cell size.

Jab ek pollen tube grow karta hai, uska growth measure kiya jaata hai by increase in its length. In contrast, ek dorsiventral leaf ka growth measure kiya jaata hai by increase in its surface area..

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2.3 Stages in the Process of Growth

Wo time jahan ek plant growth show karta hai, usually divide kiya jaata hai into three phases: meristematic phase, elongation phase, aur maturation phase. In stages ko better samajhne ke liye, hum root tips ko dekh sakte hain.

Root apex aur shoot apex me jo cells hote hain, wo continuously divide karte rehte hain, aur ye meristematic phase ka part hote hain. Ye meristematic cells me bahut saara protoplasm hota hai, aur inke paas large, clearly visible nuclei hote hain. Inke cell walls thin hote hain, cellulose se bane hote hain, aur primary nature ke hote hain. Ye cells me kai plasmodesmatal connections bhi hote hain, jo cells ke beech communication me help karte hain.

Jo cells meristematic region ke just piche (proximal) hote hain, wo elongation phase me enter karte hain. Is phase me, cells me increased vacuolation hoti hai, wo larger grow karte hain, aur new cell walls deposit karte hain.

Root tip se thoda aur piche jaane par, cells maturation phase me enter karte hain. Is phase me, cells apni full size tak pahunchte hain, unke walls thicken ho jaate hain, aur unka protoplasm change hota hai taaki wo special functions perform kar sake. Zyada tar tissues aur cell types jo aapne earlier classes me study kiye hain, wo maturation phase me belong karte hain.

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2.4 Speed at Which Growth Occurs

• Term growth speed ka matlab hai ki ek specific amount of time me kitna growth hota hai. Simple words me, ye increase in size ya number over time hai.
• Ye rate of growth mathematical expressions ka use karke calculate kiya jaa sakta hai. Ek plant ya uske kisi bhi part me more cells different ways me produce ho sakte hain.
• Growth rate do main patterns follow kar sakta hai: arithmetic growth aur dusra.
• Arithmetic growth me, jab ek cell mitosis ke through divide karta hai, sirf ek daughter cell divide karna continue karta hai, jabki doosra cell divide karna stop kar deta hai aur mature hokar apna function perform karna start karta hai.
• Arithmetic growth ka simple example hai ek root jo constant speed se grow karta hai. Agar aap is root ke length over time ka graph banate hain, toh aapko ek straight line milegi, jise linear curve bhi kehte hain.
• Arithmetic growth ka formula likha jaata hai as:
  • Lt = L₀ + rt,
    Jahan Lt hai length at time t, L₀ hai initial length, aur r hai growth rate ya elongation per unit time.
• Ab chaliye geometrical growth ko samajhte hain. Is type ke growth me, shuru me plant slowly grow karta hai — is slow start ko lag phase kehte hain. Uske baad, growth bahut fast ho jaati hai, jise log phase ya exponential phase kehte hain. Is case me, dono daughter cells jo mitosis se produce hote hain, wo divide karna continue karte hain, jiska result hota hai rapid growth. Lekin agar nutrient supply limited ho, toh growth phir se slow down karna start karta hai, aur plant stationary phase me enter karta hai. Agar aap is entire pattern of growth over time ka graph banate hain, toh ye ek S-shaped curve show karega, jise sigmoid curve kehte hain. Ye curve typical hai saare living plants, unke cells, tissues, aur organs ke liye, especially jab wo natural environment me grow karte hain.
• The formula for exponential growth is:
  W₁ = W₀ × eʳᵗ,
  Jahan W₁ hai final size (jo ho sakta hai weight, height, ya cell number), W₀ hai initial size, r hai growth rate, t hai time, aur e hai base of natural logarithms. Is formula me, r ko relative growth rate bhi kehte hain, aur ye measure karta hai ki plant kitna achha new material produce kar sakta hai. Isse efficiency index bhi kehte hain. Toh, plant part ka final size (W₁) uske initial size (W₀) par depend karta hai.
• Growth ko living systems me compare karne ke bhi do tarike hote hain. Pehla hai absolute growth rate, jiska matlab hai measure aur compare karna ki kitna total growth ek specific time me hota hai. Dusra hai relative growth rate, jiska matlab hai measure karna ki kitna plant grow karta hai ek certain time me, uske starting size ke relative.
• For example, imagine kijiye do leaves, A aur B, jo alag-alag sizes ke hain. Kuch time ke baad, dono larger ho jaate hain aur ban jaate hain A₁ aur B₁, aur even agar dono equal increase in area show karte hain, tab bhi ek ka relative growth rate zyada ho sakta hai. Ye isliye hota hai kyunki uska starting size chhota tha, toh uska growth original size ke comparison me zyada hai.

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2.5 Essential Factors Required for Growth

• Kya aap soch sakte ho ki plant growth ke liye kaunse basic needs zaruri hain? Is list me definitely water, oxygen, aur nutrients shamil honge, kyunki ye growth ke liye bahut important hain. Plant cells mainly cell enlargement ke through bade hote hain, aur is process ke liye water ki zarurat hoti hai. Jab cells water lete hain, to wo turgid (swollen) ho jate hain, aur ye turgidity plant ke parts ko stretch aur grow karne me help karti hai. Toh, plant ki growth aur development ki ability closely connected hai uske water status se. Water ek medium ke roop me bhi kaam karta hai jahan enzymes kaam kar sakte hain, aur ye enzymatic activities saari growth processes ke liye zaruri hain. Oxygen bhi ek important role play karta hai — ye metabolic energy release karne me help karta hai jo growth activities ke liye essential hai. Plants ko nutrients bhi chahiye, jisme dono macronutrients aur micronutrients shamil hain. Ye nutrients protoplasm (cells ka living part) banane aur energy ke source ke liye required hain.
• Iske alawa, har plant ka ek specific optimum temperature range hota hai jahan wo best grow karta hai. Agar temperature is range ke comparison me bahut high ya bahut low ho jaye, to ye plant ko harm kar sakta hai ya uski growth ko rok bhi sakta hai. Saath hi, environmental signals jaise light aur gravity bhi plant ke different stages of growth ko affect kar sakte hain.

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3. Cell Specialization, Reversal, and Re-acquisition of Function

• Jo cells root apical meristem, shoot apical meristem, aur cambium se aate hain, wo baad me changes se guzarte hain taaki wo specific functions perform kar sakein. Ye process, jahan cells mature aur specialized ho jate hain, usse differentiation kehte hain. Differentiation ke dauran, ek cell me bahut saare structural changes hote hain, dono cell wall aur protoplasm me. For example, jab ek plant tracheary elements banata hai (jo water transport me help karte hain), to cells apna protoplasm completely lose kar dete hain. Ye cells strong, elastic secondary cell walls bhi develop karte hain jo lignocellulose se bane hote hain, aur ye unhe long distances tak water carry karne me help karte hain, even jab tension bahut high ho. Aap try kar sakte ho ki in anatomical structures ko unke functions ke saath connect karo jo plant ke different parts me perform hote hain.
• Plants ek bahut hi interesting feature bhi dikhate hain. Kabhi-kabhi, even fully mature cells jo already differentiated ho chuke hote hain aur jinke paas divide karne ki ability nahi hoti, wo certain conditions me dobara dividing start kar sakte hain. Is special ability ko dedifferentiation kehte hain. Ek acha example hai jab interfascicular cambium ya cork cambium already mature parenchyma cells se form hota hai. Jab ye hota hai, newly formed meristematic tissues dobara divide karna start kar dete hain, aur ye cells eventually stop dividing karke mature ho jate hain taaki specific tasks perform kar sakein. Is process ko redifferentiation kehte hain. Ek woody dicot plant me, bahut saare tissues hote hain jo redifferentiation ke through form hote hain — aap try kar sakte ho ki unhe examples ke roop me list karo.
• Ab socho ki tumour kaise banta hai. Ye ek abnormal growth of cells hota hai. Plant tissue culture me, jab parenchyma cells ko controlled laboratory setting me divide karwaya jata hai, to unhe aap kya call karoge? Ye bhi dedifferentiated cells ke examples hain.
• Humne mention kiya tha ki plant growth open hoti hai, matlab ye long time tak continue kar sakti hai (isko indeterminate growth bhi kehte hain) ya fir ek certain point ke baad stop ho sakti hai (determinate growth). Ab, hum ye bhi keh sakte hain ki differentiation plants me open hai. Iska reason ye hai ki same meristem different types ke cells ya tissues produce kar sakta hai depending on ki wo plant ke kis part me ban rahe hain. Ek cell ya tissue ka final structure aur function kaafi depend karta hai uske position par plant me. For example, jo cells root apical meristem se door hote hain, wo root cap cells ban jate hain, aur jo cells root ke outer edge ki taraf push hote hain, wo epidermis ban jate hain. Aap other examples bhi soch sakte ho jahan ek cell ki position decide karti hai ki wo plant organ me kaunsa type ka cell banega — ye clear sign hai open differentiation ka.

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4. Overall Progression in Structure and Function of an Organism

Development ka matlab hai saare changes jo ek organism me uski poori life cycle ke dauran hote hain, starting from germination of the seed tak jab tak plant senescence tak pahuchta hai, matlab uske life ka final stage. Isme saare stages aur transformations shamil hain jo plant apni life ke beginning se end tak undergo karta hai.

Ek diagram jo sequence of processes dikhata hai jo ek plant cell ke development me involved hote hain. Ye diagram sirf individual cells ke liye nahi, balki tissues aur organs ke development ke relation me bhi samjha ja sakta hai higher plants me. In steps me different processes shamil hote hain jo ek cell ko change aur mature hone me help karte hain poori life ke dauran.

Plants alag-alag tarike se grow kar sakte hain depending on unke environmental conditions ya unke life cycle ke stage par. Ye different situations ke basis par plants alag structures develop kar sakte hain. Is ability ko plasticity kehte hain. Ek acha example hai plants jaise cotton, coriander, aur larkspur, jahan young (juvenile) plants ke leaves ka shape mature plants ke leaves se alag hota hai. Ye leaf shape me time ke sath hone wale change ko heterophylly kehte hain.

Kuch plants me, jaise buttercup, leaves ka shape depend karta hai ki wo air me grow kar rahe hain ya water me. Ye ek aur type ka heterophyllous development hai, lekin is case me change age ki wajah se nahi, balki environmental conditions ki wajah se hota hai. Ye example bhi plasticity ka concept dikhata hai, jahan same plant alag-alag forms ke leaves develop kar sakta hai depending on uske surroundings.

Ek plant cell me developmental process me ek series of steps shamil hote hain. Ye start hota hai cell division se, fir plasmatic growth, elongation (expansion), differentiation, maturation, aur finally death ya senescence tak. Ye complete cycle ek meristematic (actively dividing) cell ko mature cell me badal deta hai. General me, development ko growth aur differentiation ka combined result maana jata hai. Ye processes dono internal (intrinsic) aur external (extrinsic) factors se control hote hain. Intrinsic factors me genetic material jo cells ke andar hota hai aur chemical signals jaise plant growth regulators shamil hote hain jo cells ke beech kaam karte hain. Dusri taraf, extrinsic factors environment se aate hain, jaise light, temperature, water, oxygen, aur nutrients.

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5. Chemical Substances Controlling Plant Growth and Development

5.1 Distinctive Features or Traits

Plant growth regulators (PGRs) chhote aur simple molecules hote hain jo kaafi different chemical structures rakh sakte hain. Inme kuch include hain indole compounds jaise indole-3-acetic acid (IAA), adenine-based molecules jaise kinetin (N6-furfurylamino purine), carotenoid derivatives jaise abscisic acid (ABA), terpenes jaise gibberellic acid (GA3), aur even gases jaise ethylene (C2H4). Scientific writings me, ye substances kabhi plant growth substances, plant hormones, ya phytohormones ke naam se bhi jaane jate hain. Naam alag ho sakta hai, lekin ye sab same category ke compounds ko refer karte hain jo plants me various processes regulate karte hain.

Ye plant growth regulators generally do main groups me divide kiye jate hain depending on ki ye plant me kya kaam karte hain. Pehla group hota hai growth-promoting regulators ka. Ye important processes me help karte hain jaise cell division, cell enlargement, pattern formation, tropic movements, flowering, fruit development, aur seed formation. In roles ki wajah se, inhe aksar plant growth promoters kaha jata hai. Inke main examples hain auxins, gibberellins, aur cytokinins.

Dusra group of PGRs plants ko damage ya stress ke response me help karta hai, jo ki living organisms (biotic) ya non-living factors (abiotic) ki wajah se ho sakta hai. Ye regulators growth ko slow karte hain aur actions jaise dormancy (jab growth temporarily stop ho jati hai) aur abscission (leaves, flowers, ya fruits ka girna) me responsible hote hain. Is type ka main example hai abscisic acid (ABA). Ek gaseous plant hormone bhi hai jise ethylene kehte hain, jo unique role play karta hai. Ye growth promoter ya inhibitor dono ke roop me kaam kar sakta hai, lekin zyada cases me ise growth inhibitor mana jata hai.

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5.2 Uncovering the Existence of Growth-Controlling Substances in Plants

Ye kaafi interesting hai ki saare five main types of plant growth regulators (PGRs) ka discovery accident se hua. Ye story start hui Charles Darwin aur unke bete Francis Darwin se, jinhone canary grass study karte waqt ek important observation kiya. Unhone notice kiya ki coleoptile (young shoot ke upar protective covering) light ki taraf bend hota hai jab light sirf ek side se padti hai. Is movement ko phototropism kehte hain. Kai experiments karne ke baad, unhone pata lagaya ki coleoptile tip responsible hai signal bhejne ke liye jo poore structure ko light ki taraf bend karwata hai. Baad me, ek scientist F.W. Went ne oat seedlings ke coleoptile tips se ek substance isolate kiya, jo is bending ke liye responsible tha. Is substance ko auxin naam diya gaya, pehla known plant growth hormone.

Ek aur major discovery hui ek strange disease ki wajah se rice plants me, jise ‘bakanae’ ya foolish seedling disease kehte hain. Disease se affected rice seedlings bahut tall aur weak grow karte the. 1926 me, ek scientist E. Kurosawa ne paaya ki even jab rice seedlings ko sterile (germ-free) liquid diya jata jo Gibberella fujikuroi fungus se liya gaya tha, to bhi wo similar abnormal growth dikhate the. Baad me, fungus me active compound identify hua as gibberellic acid, jo ek type ka gibberellin hai, aur ab ise growth-promoting PGR ke roop me jaana jata hai.

Aage ka progress kiya F. Skoog aur unki team ne, jinhone tobacco plant stems ke pieces study kiye. Unhone paaya ki ek mass of undifferentiated cells, jise callus kehte hain, sirf tab grow aur multiply karta hai jab auxins ke sath kuch substances jaise vascular tissue extracts, yeast extract, coconut milk, ya even DNA present ho. 1955 me, ek scientist Miller aur unke colleagues ne identify aur crystallize kiya active substance jo cytokinesis (cell division) ko promote karta tha. Is new growth substance ko unhone kinetin naam diya, jo ek type ka cytokinin hai.

1960s ke mid me, teen alag-alag scientist groups ne independently teen separate substances discover kiye jo plant growth ko inhibit karte the. Ye the inhibitor-B, abscission II, aur dormin. Lekin later studies ne prove kiya ki ye teeno actually same chemical compound the. Ye single substance eventually naam diya gaya abscisic acid (ABA), aur ye ek major growth-inhibiting PGR ke roop me jaana gaya.

Final discovery kaafi pehle, 1910 me, H.H. Cousins ne ki. Unhone notice kiya ki ripe oranges ek gaseous substance release karte hain jo nearby unripe bananas ko jaldi ripen karwata hai. Ye gas later identify hua as ethylene, ek gaseous plant growth regulator jo fruit ripening ko influence karta hai. Ethylene ab widely known hai apne role ke liye kai plant processes me, including senescence aur abscission.

Ab jab hum samajh gaye ki ye five major categories of PGRs—auxins, gibberellins, cytokinins, abscisic acid, aur ethylene—kaise discover hui, hum unke effects on plant physiology ko next section me seekh sakte hain.

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5.3 Impact of Growth Substances on Plant Functions

1. Auxins

Auxins ek type ka plant growth regulator hain, jiska naam Greek word ‘auxein’ se aaya hai, jiska matlab hai “to grow.” Pehla auxin actually human urine se isolate kiya gaya tha. Term “auxin” usually refer karta hai indole-3-acetic acid (IAA) ko, saath hi other natural aur synthetic compounds jo plant growth control karte hain. Auxins mostly growing tips (apices) of stems aur roots me bante hain aur fir un areas me transport hote hain jahan wo act karte hain. Natural auxins ke examples hain IAA aur indole butyric acid (IBA). Kuch commonly used synthetic auxins hain NAA (naphthalene acetic acid) aur 2,4-D (2,4-dichlorophenoxyacetic acid). Ye compounds agriculture aur horticulture me widely use hote hain.

Auxins plants me kai important roles play karte hain. Ye root formation me help karte hain stem cuttings se, jo ek common method hai plants propagate karne ka. Ye flowering me bhi help karte hain, jaise pineapple plants me, aur early fruit ya leaf drop prevent karte hain. Lekin ye older leaves aur fruits ke falling (abscission) ko promote karte hain. Kai plants me, main growing shoot (apical bud) side buds (axillary buds) ko grow karne se rokta hai, is phenomenon ko apical dominance kehte hain. Agar shoot ka tip remove kar diya jaye (process ko decapitation kehte hain), to lateral buds grow karna start karte hain. Ye technique commonly tea gardens aur hedges banane ke liye use hoti hai.

Auxins parthenocarpy bhi cause kar sakte hain, matlab fruit formation without fertilization, jaise tomatoes me. Ye herbicides ke roop me bhi use hote hain. For example, 2,4-D broad-leaved weeds (dicots) ko maar deta hai, lekin monocot crops jaise grass ko harm nahi karta. Gardeners ise use karte hain lawns ko weed-free rakhne ke liye. Auxins xylem formation ko bhi influence karte hain aur cell division me help karte hain.

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2. Gibberellins

Gibberellins ek aur group hain growth-promoting plant hormones ka. 100 se zyada gibberellins different organisms me paye gaye hain, jaise fungi aur higher plants. In hormones ko label kiya jata hai GA1, GA2, GA3, aur aise hi aage. Sabse well-known type hai Gibberellic acid (GA3), jo pehla discover hua aur abhi tak sabse zyada study kiya gaya hai. Saare gibberellins acidic nature ke hote hain. Ye plants me kai important effects produce karte hain. For example, ye plant stem ka length increase karne me help karte hain, jo grape stalks ko lamba banane me use hota hai. Apples me ye fruits ko bada aur better shape me grow karne me help karte hain. Gibberellins senescence ko delay karte hain, matlab fruits tree par zyada time tak reh sakte hain aur unka market life lamba ho jata hai.

Brewing industry me, GA3 use hota hai malting process ko speed up karne ke liye, jo beer banane ke liye essential hai. Sugarcane me, jo sugar stem me store karta hai, gibberellins spray karne se stems lamba hote hain, jo yield ko 20 tonnes per acre tak badha sakta hai. Young conifer plants me, gibberellins plant ko faster mature karne me help karte hain, taaki wo seeds jaldi produce karna start kare. Gibberellins bolting me bhi help karte hain, jo rapid stem growth hai flowering se pehle, jo plants me dekha jata hai jaise beet aur cabbage.

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3. Cytokinins

Cytokinins ek group hain plant hormones ka jo mainly cell division (cytokinesis) me help karte hain. Ye pehli baar discover hue substance kinetin se, jo isolate kiya gaya tha autoclaved herring sperm DNA se. Interestingly, kinetin khud plants me naturally nahi hota, lekin isne scientists ko natural cytokinins dhundhne ke liye inspire kiya. Is search me zeatin discover hua, jo corn kernels aur coconut milk me paya jata hai. Tab se, kai natural aur synthetic cytokinins identify kiye gaye. Ye hormones un areas me bante hain jahan cell division active hoti hai, jaise root tips, developing buds, aur young fruits.

Cytokinins help karte hain new leaves produce karne me, chloroplasts form karne me leaves me, side shoots ka growth promote karne me, aur adventitious shoots ke growth ko encourage karte hain. Ye auxins ke effect ko bhi counter karte hain by reducing apical dominance. Ek aur important role of cytokinins hai nutrients ko mobilize karna, jo help karta hai aging (senescence) of leaves ko delay karne me.

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4. Ethylene

Ethylene ek gaseous plant hormone hai jo large amounts me produce hota hai aging plant tissues aur ripening fruits ke dwara. Iska plant development par kai effects hote hain. Ye horizontal growth cause karta hai seedlings me, swelling of plant stems karta hai, aur dicot seedlings me apical hook create karta hai. Ethylene promote karta hai aging aur shedding (senescence and abscission) of plant parts jaise leaves aur flowers. Iska ek sabse important role hai fruit ripening me, jahan ye respiration rate ko increase karta hai fruits me, ek phenomenon jo respiratory climactic kehlaata hai.

Ethylene seed aur bud dormancy ko break kar sakta hai, peanut seed germination me help karta hai, aur potato tubers ko sprout karwata hai. Ye deep-water rice plants me stems aur leaf stalks ko elongate karta hai, jo plant parts ko water ke upar rehne me help karta hai. Ethylene root growth aur root hairs formation ko promote karta hai, jisse plant ki water aur nutrients absorb karne ki ability badh jati hai. Ye flowering trigger karne aur crops jaise pineapple me fruit development synchronize karne ke liye bhi use hota hai. Mango me ethylene flower formation me help karta hai.

Ethylene agriculture me extensively use hota hai kyunki ye kai plant activities regulate karta hai. Ek compound ethephon commonly use hota hai source of ethylene ke roop me. Jab plants par spray kiya jata hai, ethephon absorb hota hai aur slowly ethylene gas release karta hai. Ye help karta hai fruits jaise tomatoes aur apples ko ripen karne me, aur crops jaise cotton, cherry, aur walnut me extra flowers aur fruits remove karne me. Ye female flowers development ko cucumbers me encourage karta hai, jisse unka yield badhta hai.

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5. Abscisic Acid (ABA)

Abscisic acid (ABA) apne role ke liye jaana jata hai leaf fall (abscission) aur dormancy me. Lekin ye plant growth aur development ke kai aur aspects ko bhi affect karta hai. ABA mostly kaam karta hai plant growth inhibitor ke roop me aur plant metabolism ko slow karta hai. Ye seeds ko too early germinate hone se rokta hai aur plants ko energy conserve karne me help karta hai stress ke time. ABA stomata (leaves ke tiny pores) ko close karwata hai, jisse plant drought ya other harsh conditions me survive kar sakta hai, isliye ise aksar “stress hormone” kehte hain.

ABA seeds ke development, maturation, aur dormancy me bhi important hai, especially dry periods ke dauran. Seeds ko dormant rakh kar, ABA unhe harsh conditions jaise dryness ya extreme temperatures se bachata hai. Kai baar, ABA aur gibberellins (GAs) ek dusre ke against kaam karte hain. Jab GAs growth promote karte hain, ABA zarurat padne par ise slow kar deta hai.

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6. Combined Action of PGRs

Har stage of plant’s growth, development, aur differentiation ek ya zyada plant growth regulators (PGRs) dwara control hoti hai. Kabhi ye ek dusre ko help karte hain (isko synergistic effects kehte hain), aur kabhi ye ek dusre ke opposite kaam karte hain (isko antagonistic effects kehte hain). Plant ki life ke kai important events, jaise seed dormancy, leaf fall (abscission), aging (senescence), aur apical dominance, multiple PGRs ke interaction ki wajah se hote hain.

Ye yaad rakhna important hai ki PGRs plants me internal control system ka sirf ek part hain. Genes (genomic control) aur external environmental factors ke sath, PGRs plant ke growth ko control karne me key role play karte hain. Factors jaise light aur temperature, jo external (extrinsic) hain, bhi plant growth ko influence karte hain by affecting hormone activity. Kuch major plant events jaise flowering, vernalisation, dormancy, germination, aur movement of plant parts dono, environmental signals aur plant hormones ke dwara regulate hote hain.

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6. Brief Overview of Key Concepts

• Growth ek bahut noticeable feature hai sabhi living things me. Iska matlab hai permanent increase in things jaise size, area, length, height, volume, aur number of cells. Ye increase hota hai protoplasmic material ke rise ki wajah se, jo cells ke andar living part hota hai.
• Plants me, jahan growth hoti hai un regions ko meristems kehte hain. Ye special tissues hote hain jo roots aur shoots ke tips me paye jate hain, jise root aur shoot apical meristems kehte hain. Kabhi, teesra type of meristem, intercalary meristem, bhi plant body ke length ko increase karne me help karta hai. Bade plants me, ye growth continuous hoti hai aur isse indeterminate growth kehte hain.
• Jab cells apical meristems me divide karte hain, growth ka type arithmetic ya geometrical ho sakta hai. Lekin growth hamesha same fast rate par continue nahi hoti; ye usually time ke sath slow ho jati hai. Generally, growth ke teen main phases hote hain – lag phase (slow start), log phase (rapid growth), aur senescent phase (decline in growth).
• Jab ek cell divide karna band kar deta hai, to wo apni structure change karna start karta hai specific function ke liye. Is change ko differentiation kehte hain. Differentiation ke dauran, cell special parts develop karta hai jo uske kaam me help karte hain. Ye rule cells, tissues, aur organs ke development par bhi apply hota hai.
• Kabhi-kabhi, differentiated cell apni pehli state me wapas ja sakta hai; ise dedifferentiation kehte hain. Baad me, ye fir se specialized cell ban sakta hai, jise redifferentiation kehte hain. Plants me ye process open hoti hai, matlab cells ke paas zarurat ke hisaab se change hone ki ability hoti hai. Isliye, plants me development (jo growth aur differentiation dono include karta hai) flexible hota hai.
• Is flexibility ko plasticity kehte hain. Iska matlab hai ki plants apna growth aur development change kar sakte hain surrounding situation ke hisaab se.
• Plant growth aur development dono internal aur external factors se control hote hain. Internal factors mainly chemicals hote hain jo plant ke andar hote hain aur jise plant growth regulators (PGRs) kehte hain. Ye five main types ke hote hain – auxins, gibberellins, cytokinins, abscisic acid, aur ethylene.
• Ye PGRs plant ke different parts me bante hain aur kai processes jaise differentiation aur development ko control karte hain. Ek single PGR plant par kai physiological effects (body functions) la sakta hai. Alag-alag PGRs kabhi-kabhi similar kaam bhi kar sakte hain. Ye together (synergistic effect) kaam kar sakte hain ya ek dusre ke opposite (antagonistic effect) kaam kar sakte hain.
• Internal factors ke alawa, external factors bhi plant growth aur development ko affect karte hain. Inme include hain light, temperature, nutrients, oxygen levels, aur gravity.

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