Plant Growth and Development: Class 11 Biology Chapter 13 Hinglish mein

Monsoon shuru hote hi aam ki guthli geeli zameen par phenk do, aur kuch hafton baad jahan woh giri thi wahan naram, latakti pattiyon wala ek laal-sa shoot khada milta hai. Kuch dashakon mein wahi shoot ek ped ban sakta hai jo har spring mein flower deta hai, garmiyon mein fruit deta hai, aur aakhir mein boodha hokar mar jaata hai. Inmein se kuch bhi random nahi hota: roots pattiyon se pehle aati hain, pattiyan flowers se pehle, flowers fruit se pehle, aur har organ apni sahi jagah par banta hai (Fig. 13.1).

Root-hair cell, xylem vessel aur petal cell dikhne aur kaam karne mein bilkul alag hain, phir bhi teeno ek hi single cell, zygote, se aaye hain. Ek cell itne saare types mein kaise badal gaya, aur plant ko kaun batata hai ki ab leaves banana band karo aur flowers banana shuru karo? Biologists iska jawab do ideas se dete hain jo milkar development (परिवर्धन) banate hain: growth, jo plant ko bada banati hai, aur differentiation, jo uske cells ko alag-alag banata hai.

Sab kuch germination se shuru hota hai, lekin seed is baare mein choosy hota hai ki kab. May mein dhool bhari sadak ke kinare pade grass ke seeds hafton tak waise hi pade rehte hain, zinda lekin lagbhag idle, ek suspended growth ki state mein. Pehli achhi baarish yeh badal deti hai: seeds paani peete hain, respiration aur enzyme activity phir shuru hoti hai, aur root bahar nikalti hai. Plant grow karne, flower dene ya rest karne se pehle kaun se signals padhta hai? Kuch uske andar se aate hain (intrinsic factors, jaise genes aur chemical messengers) aur kuch bahar se (extrinsic factors, jaise light, temperature aur paani). Yeh chapter dono ko dekhta hai.

13.1 Growth

Kisi se bhi poocho ki plant zinda hai yeh kaise pata chalta hai, to sabse pehle jawabon mein 'woh badhta hai' hoga. Biologists is word ko ek narrow sense mein use karte hain: growth (वृद्धि) kisi cell, organ ya poore organism ke size mein ek irreversible, permanent increase hai. Iski keemat metabolism chukata hai: anabolic reactions naya protoplasm aur wall material banate hain aur respiration jaise catabolic reactions energy dete hain. Tane par kai mahino tak phoolta kathal grow kar raha hai, kyunki woh kabhi apne pehle size mein wapas nahi sikudega.

13.1.1 Plant Growth Aam Taur par Indeterminate Hoti hai

Zyadatar animals adult size par pahunchkar badhna band kar dete hain. Kai plants kabhi band nahi karte: ek bargad sadiyon tak roots, branches aur wood jodta reh sakta hai. Woh yeh hamesha young rehne wale tissue ke chhote pockets rakhkar karte hain, jinhe meristems (विभज्योतक) kehte hain. Jab meristem cell divide hota hai, to ek daughter aam taur par meristem mein hi rehta hai jabki doosra side mein dhakel diya jaata hai, jaldi divide karna band kar deta hai aur mature hokar body ka hissa ban jaata hai. Isliye meristem plant banate hue bhi khud ko renew karta rehta hai.

Kyunki meristems plant ki poori life tak cells dete rehte hain, botanists plant growth ko open, ya indeterminate, kehte hain. Lekin har organ open-ended nahi hota: leaf, flower ya fruit ek fixed size tak badhkar ruk jaata hai, yeh determinate growth hai.

Meristems kahan hain, isse tay hota hai ki plant kis direction mein badhega (Fig. 13.2). Dono tips ke meristems, shoot apical meristem aur root apical meristem, plant ko uske axis ke along lamba karte hain: yeh primary growth hai. Plant ke establish hone ke baad dicots aur gymnosperms ek doosra set jodte hain: vascular cambium aur cork cambium, jinhe lateral meristems kehte hain kyunki yeh stems aur roots ki sides ke along chalte hain. Inke divisions sideways layers jodte hain, to stems aur roots mote hote hain; yeh secondary growth hai. Grasses aur bamboo mein internodes aur leaves ke base par intercalary meristems bhi hote hain, isiliye kata hua lawn neeche se phir ugg aata hai.

13.1.2 Growth Measurable Hai

Cell ke grow karne par asal mein jo jama hota hai woh protoplasm hai, lekin root tip ke protoplasm ko koi balance par nahi rakh sakta. Isliye hum ek proxy track karte hain jo uske saath badhta hai, jaise fresh weight, dry weight, length, area, volume ya cells ki sankhya, aur sahi proxy is par depend karta hai ki kya grow kar raha hai (Table 13.1).

Koi ek yardstick plant ki poori life ke liye kaam nahi karta. Bhiga hua chana paani lene ki wajah se jaldi fresh weight badhata hai, lekin pehle kuch dinon tak uska dry weight girta hai: leaves ke photosynthesis shuru karne se pehle woh stored food jalata hai. Life ke aakhir mein leaf fall aur seed shedding se weight records girte hain jabki plant abhi zinda hai. Isliye biologists measure ko organ aur stage se match karte hain, aur aksar ek se zyada measures use karte hain.

13.1.3 Growth ke Phases

Badhti root tip ko lambai mein kaato aur tumhe growth space mein bichhi hui dikhegi (Fig. 13.3). Root cap ke theek peeche cells baar-baar divide karte hain: meristematic phase. Thoda aur peeche naye cells divide karna band karke khinchte hain: elongation phase. Aur peeche cells apna final form le lete hain: maturation phase. Shoot tip mein bhi yahi sequence dikhta hai. Har cell baari-baari teeno phases se guzarta hai, isliye yeh zones root ke along jami hui ek timeline jaise hain.

13.1.4 Growth Rates

Koi cheez kitni tezi se badhti hai, woh uska growth rate hai: unit time mein size ka increase. Iske peeche cell division ke do bilkul alag patterns ho sakte hain (Fig. 13.4).

Arithmetic growth mein har division ke baad ek daughter divide karta rehta hai aur ek ruk kar mature hota hai. Divide hone wala cell ek press ki tarah kaam karta hai jo har round mein ek finished cell nikalta hai, to organ har interval mein utna hi badhta hai. Ek aisi root socho jo har ghante utni hi length jodti hai: time ke against plot karne par uski length ek seedhi line deti hai (Fig. 13.5):

Geometric growth mein dono daughters divide karte rehte hain, to har round mein cell number double hota hai. Real systems ise lambe samay tak jaari nahi rakh sakte. Growth ek lag phase mein dheere shuru hoti hai, log ya exponential phase mein tez hoti hai, phir nutrients kam padne par stationary phase mein sapaat ho jaati hai. Tab size vs time ka graph S-shape ka hota hai, ek sigmoid curve. Culture mein cells, organs aur natural surroundings mein badhte poore plants, sab yahi curve banate hain. Embryo dono patterns use karta hai: uske pehle divisions geometric hote hain, phir sirf kuch regions divide karte rehte hain jabki baaki differentiate ho jaate hain.

Exponential phase ek simple law follow karta hai:

Is law mein constant $r$ relative growth rate hai: pehle se maujood material ki har unit se unit time mein bana naya material. Yeh naapta hai ki plant jo uske paas pehle se hai use kitni efficiently aur zyada khud mein badalta hai, isliye ise efficiency index bhi kehte hain. Dhyaan do ki $W_1$ $W_0$ ke proportional hai: same $r$ aur $t$ ke saath, jo plant do guna bada shuru hota hai woh do guna bada hi khatam hota hai. Natural logarithms lene par $r=\frac{1}{t}\ln (W_1\mathrm{/}{W}_0)$ milta hai, aur size har $\ln 2\mathrm{/}r$ units time mein double hota hai.

Do badhte systems ko do tarah se compare kiya ja sakta hai. Absolute growth rate unit time mein total badhat hai. Relative growth rate us badhat ko starting size se divide karta hai, taaki ek seedling aur ek poore bade plant ko fairly compare kiya ja sake:11Chhote interval ke liye dono forms ek jaisa result dete hain. Exponential growth ke lambe stretch mein iski jagah $r=\frac{1}{t}\ln (W_1\mathrm{/}{W}_0)$ use karo, kyunki interval ke dauraan base bhi badhta rehta hai.

13.1.5 Growth ke liye Conditions

Khidki par rakha seedling kis cheez ke bina mar jaayega? Uski har zaroorat ka ek pakka kaam hai:

• Paani. Cells paani lekar bade hote hain, aur isse bana turgor extension growth ke dauraan wall ko bahar dhakelta hai. Naya material banane wale enzyme reactions ko bhi ek aqueous medium chahiye.
• Oxygen. Aerobic respiration ko iski zaroorat hai taaki woh energy release ho jo naye cells banane mein kharch hoti hai.
• Nutrients. Macronutrients aur micronutrients naye protoplasm ke liye raw material dete hain, aur kuch energy ke source ka kaam bhi karte hain.
• Temperature. Har plant ek optimum range mein sabse achha badhta hai; kisi bhi taraf zyada door jaao to growth dheemi hoti hai, ruk jaati hai ya plant mar jaata hai.
• Light aur gravity. Yeh signals ki tarah kaam karte hain jo khaas stages ko steer karte hain, jaise shoot kis taraf mudega ya seedling kab hara hoga.

13.2 Differentiation, Dedifferentiation aur Redifferentiation

Root apical meristem ke ek cell ko teak ke tane ki wood ke ek vessel element se compare karo. Dono meristems se aaye, phir bhi ek protoplasm se bhara ek chhota zinda dabba hai, aur doosra ek mara hua, khokhla pipe. Iski moti lignocellulosic secondary wall, mazboot lekin elastic, ise collapse hone se bachati hai jab iske through paani zyada tension mein upar khincha jaata hai. Pehle type ke cell se doosre tak, ya kisi bhi doosre specialised cell tak, ka safar differentiation (विभेदन) hai. Kuch cells raaste mein sirf thoda badalte hain, kuch bahut zyada, aur yeh changes wall, protoplasm ya dono mein ho sakte hain.

Plant cells film ko ulta bhi chala sakte hain. Jab ek woody dicot stem mota hona shuru karta hai, to kuch parenchyma cells jo kab se divide karna band kar chuke the, division phir se on kar dete hain: vascular bundles ke beech wale cells interfascicular cambium ban jaate hain, aur cortex ke kuch cells cork cambium ban jaate hain. Jo mature, zinda cell is tarah phir se divide karna shuru karta hai, usmein dedifferentiation (निर्विभेदन) hua hai. In naye meristems se bane cells jaldi settle ho jaate hain, divide karna band karte hain aur khaas roles le lete hain; yeh doosri baar mature hona redifferentiation (पुनर्विभेदन) hai. Secondary xylem, secondary phloem, cork aur secondary cortex sab iske products hain (Fig. 13.8).

Openness growth ki tarah differentiation par bhi laagu hoti hai (Section 13.1.1). Meristem ek hi standard product nahi nikalta: uske derivatives kaafi alag cells mein mature hote hain, aur cell kahan pahunchta hai, iska uski kismat mein bada haath hota hai. Root apex par, meristem se aage tip ki taraf khiske cells root-cap cells bante hain, jabki side mein surface ki taraf khiske cells epidermis bante hain. Vascular cambium sideways yahi rule follow karta hai: uske andar ki side ke derivatives xylem bante hain aur bahar ki side wale phloem.

13.3 Development

Development mein organism ki life ka har change aata hai, seed ke germinate hone ke pal se lekar uske boodha hokar senesce hone tak. Ek single cell ke liye sequence yeh hai: cell division, protoplasm ki growth (plasmatic growth), expansion ya elongation, differentiation, maturation, aur aakhir mein senescence aur death (Fig. 13.9). Tissues aur organs bhi inhi stages se guzarte hain.

Plant ka body plan pehle se fixed nahi hota: same plant apni umar ya apne surroundings ke hisaab se alag shapes ke organs bana sakta hai, is flexibility ko plasticity (सुघट्यता) kehte hain. Classic example heterophylly hai, yaani ek hi plant par ek se zyada shape ki leaves (Fig. 13.10). Dhaniye ki zameen ke paas wali pehli leaves chaudi aur lobed hoti hain, lekin baad mein upar bani leaves patle dhaagon jaisi kati hoti hain; cotton aur larkspur bhi juvenile aur adult leaf shapes ke beech switch karte hain, to yahan trigger life phase hai. Buttercup mein trigger surroundings hain: talaab ke through upar badhta shoot paani ke neeche bareek kati leaves banata hai aur hawa mein pahunchne par chaudi leaves.

Teeno ideas ko saath rakho to ek chhota formula milta hai: development = growth + differentiation. Ise steer kaun karta hai? Kuch controls plant ke andar se aate hain aur kuch bahar se:

13.4 Plant Growth Regulators

13.4.1 Characteristics

Chemically plant growth regulators (पादप वृद्धि नियामक), yaani PGRs, alag-alag tarah ke hote hain, lekin sab chhote, simple molecules hain, aur milkar growth aur development ko steer karte hain. Tumhe yeh plant hormones, phytohormones ya plant growth substances naam se bhi milenge. Paanch major classes aur unki chemical nature Table 13.3 mein di gayi hai.

Function ke hisaab se PGRs do bade groups mein aate hain. Growth promoters (auxins, gibberellins aur cytokinins) cells ka divide aur bada hona, patterns banana, tropic bending, aur flowers, fruits aur seeds banana jaisi activities chalate hain. Doosra group, growth inhibitors, plant ko chot aur stress se nipatne mein madad karta hai, chahe woh pests aur pathogens se ho ya drought aur thand se, aur dormancy aur abscission ke through growth par brake lagata hai; abscisic acid iska main member hai. Ethylene kisi bhi group mein theek se fit nahi hota, halaanki uske zyadatar actions growth ko rokte hain.

13.4.2 Plant Growth Regulators ki Discovery

Paanch mein se koi bhi class plan karke nahi mili: har ek tab saamne aayi jab scientists kisi aur sawaal ke peeche the. Kahani Charles Darwin aur unke bete Francis se shuru hoti hai. Unhone dekha ki canary grass seedlings ke coleoptiles (pehli leaf ke around ki sheaths) ek side se aati light ki taraf mudte hain, is response ko phototropism kehte hain. Alag-alag parts ko dhakkar ya hatakar unhone nateeja nikala ki tip light ko sense karti hai aur mudne wale region tak neeche ek signal bhejti hai (Fig. 13.11). Baad mein F. W. Went ne oat coleoptiles ki tips se us influence ko agar ke chhote blocks mein ikattha kiya, jisse pata chala ki yeh ek chemical hai: auxin.

Japan ke dhaan kisaan bakanae, yaani 'foolish seedling', naam ki ek bimari jaante the, jismein infected seedlings lambe aur patle ho jaate hain. Yeh fungus Gibberella fujikuroi se hoti hai. 1926 mein E. Kurosawa ne dikhaya ki fungus ka ek sterile filtrate, jismein koi zinda fungus nahi tha, healthy seedlings mein bhi wahi symptoms paida karta hai. Baad mein chemists ne dikhaya ki active compounds gibberellic acid the.

F. Skoog ki team tobacco stem ke tukdon ko culture mein badhte rakhne ki koshish kar rahi thi. Sirf auxin kaafi nahi tha: tukdon ne ek callus banaya, undifferentiated cells ka ek dher, jo tabhi badhta rehta tha jab medium mein kuch extra daala jaata, chahe coconut milk, yeast extract, vascular tissue ka extract, ya DNA. Active ingredient dhoondhte hue C. O. Miller aur saathiyon ne 1955 mein ise crystallise kiya; kyunki yeh cells mein cytokinesis karata tha, unhone iska naam kinetin rakha.

Abscisic acid ke teen birth certificates hain. 1960s ke beech tak alag-alag groups ne alag sources se growth inhibitors purify karke unhe alag naam diye the: dormin (bud dormancy se juda), abscisin II (young cotton fruits ke girne se juda) aur inhibitor-B. Chemical analysis se pata chala ki teeno ek hi molecule the, jiska naya naam abscisic acid (ABA) rakha gaya. Paanchvi class ka clue pehle hi, store kiye fruit se, mil chuka tha: 1910 mein H. H. Cousins ne report kiya ki pake santron se nikalne wali gases unke saath rakhe kachche kelon ko jaldi paka deti hain. Saalon baad chemists ne dikhaya ki zimmedaar gas ethylene thi.

13.4.3 Plant Growth Regulators ke Physiological Effects

13.4.3.1 Auxins

Auxin ka naam Greek auxein se aaya hai, jiska matlab 'badhna' hai. Ajeeb baat hai ki sabse pehla isolate kiya gaya auxin kisi plant se nahi balki human urine se mila tha. Aaj yeh word ek poori family ke liye hai: indole-3-acetic acid (IAA) aur indole butyric acid (IBA), jo plants banate hain, aur lab mein bane naphthalene acetic acid (NAA) aur 2,4-dichlorophenoxyacetic acid (2,4-D) jaise compounds jo usi tarah kaam karte hain. Plant ke andar auxin zyadatar badhte shoots aur roots ki tips par banta hai aur wahan se un cells tak jaata hai jin par woh kaam karta hai. Kisaan aur gardeners poori family ko kaam mein lagate hain:

• Weed control. 2,4-D dicot weeds ko maar deta hai lekin mature monocots par asar nahi karta, isliye gardeners lawns ko weed-free rakhne ke liye ise use karte hain.
• Cuttings mein roots. Stem cutting ke kate sire ko auxin se treat karne par roots shuru hoti hain, yeh plants ko propagate karne ka ek standard tarika hai.
• Seedless fruit. Auxins parthenocarpy induce karte hain, yaani bina fertilisation ke fruit banna, jaise tomato mein.
• Flowering. Yeh flowering ko promote karte hain, jaise pineapple mein.
• Pakad kar rakhna, phir chhod dena. Yeh young fruits aur leaves ko jaldi girne se rokte hain, lekin purani, mature leaves aur fruits ko gira dete hain (abscise).
• Plant ke andar. Auxin yeh bhi control karta hai ki xylem kaise differentiate ho, aur cell division mein madad karta hai.

Sunflower ka stem dekho to har leaf ke kone mein buds khaali baithi dikhengi. Unhe top par badhti bud rok kar rakhti hai, is effect ko apical dominance kehte hain. Us apical bud ko kaat do (decapitation) to cut ke neeche ki buds aam taur par side branches ke roop mein badhne lagti hain (Fig. 13.12). Chai todne wale iska fayda uthate hain: shoot tips ko baar-baar hatakar woh jhaadiyon ko kamar tak ooncha aur naram naye shoots se bhara rakhte hain. Hedge ko kaatna bhi isi tarah kaam karta hai, jisse woh ghana aur bhara hua ho jaata hai.

13.4.3.2 Gibberellins

Gibberellins promoters ki sabse badi family hain: 100 se zyada pata hain, fungi aur flowering plants dono se. Naam ki jagah inke numbers hote hain ($\mathrm{G}{\mathrm{A}}_1$, $\mathrm{G}{\mathrm{A}}_2$, $\mathrm{G}{\mathrm{A}}_3$ waghairah), aur har ek acid hai. Sabse famous aur sabse zyada study kiya gaya gibberellic acid, $\mathrm{G}{\mathrm{A}}_3$, hai, jo sabse pehle milne walon mein se ek tha. Gibberellins kya karte hain, aur growers inhe kaise use karte hain:

• Bolting. Yeh beet, cabbage aur rosette habit wale doosre plants mein bolting promote karte hain, yaani flowering se theek pehle internodes ka tezi se lamba hona.
• Sugarcane. Yeh fasal apne stem mein sugar store karti hai; ispar gibberellins spray karne se stem lamba hota hai aur harvest mein per acre 20 tonnes tak ganna badh sakta hai.
• Lambe axes. Yeh axis ko lamba karte hain, isliye growers angoor par spray karte hain taaki gucchhon ke stalks lambe hon.
• Fruit shape. Yeh apple jaise fruits ko lamba aur behtar shape ka banate hain.
• Der se senescence. Fruit ped par zyada der tak reh sakta hai, jisse market period lamba hota hai.
• Conifers mein jaldi seed. Juvenile conifers par spray karne se maturity jaldi aati hai, to woh jaldi seed dete hain.
• Brewing. $\mathrm{G}{\mathrm{A}}_3$ brewing industry mein malting ko tez karta hai.

13.4.3.3 Cytokinins

Jaisa naam batata hai, cytokinins cytokinesis, yaani cytoplasm ke division, par kaam karte hain. Plants inhe wahan banate hain jahan cells tezi se divide hote hain: root apices, develop hoti shoot buds aur young fruits mein. Lekin pehla mila cytokinin plant ka product tha hi nahi. Kinetin, ek modified adenine (ek purine), herring sperm DNA se mila tha jise autoclave mein garam kiya gaya tha, aur yeh plants mein naturally nahi milta. Same activity wale natural compound ki khoj zeatin par khatam hui, jo maize (corn) ke daanon aur coconut milk se mila, aur tab se bahut saare natural aur synthetic cytokinins pehchane ja chuke hain. Inke effects:

• Yeh leaf mein nutrient mobilisation promote karte hain, jisse leaf senescence der se hoti hai.
• Yeh tip ke auxin ke against kaam karke apical dominance ko overcome karne mein madad karte hain.
• Yeh lateral shoot growth aur adventitious shoots banne ko promote karte hain.
• Yeh nayi leaves, aur leaves mein chloroplasts, banane mein madad karte hain.

13.4.3.4 Ethylene

Ethylene ($\mathrm{C}{\phantom{X}}_2\mathrm{H}{\phantom{X}}_4$), paanch classes mein akeli gas, ripening hormone ke roop mein sabse famous hai. Pakte hue fruits aur boodhe hote tissues ise bahut zyada matra mein chhodte hain, aur badle mein yeh gas pakne ko tez karti hai: yeh fruit ke respiration rate ko ek uchhaal mein badha deti hai jise respiratory climacteric kehte hain (Fig. 13.13). Yeh plant organs, khaas kar leaves aur flowers, ke boodhe hone aur girne ko tez karti hai. Dicot seedlings par iska ek kamaal ka teen-tarfa effect hota hai: seedling side mein badhta hai, uska axis phool jaata hai, aur uski tip mud kar ek apical hook ban jaati hai.

Ethylene ke kai aur effects bhi hain:

• yeh deep-water rice ke internodes aur petioles ko tezi se lamba karti hai, jisse leaves aur upar ka shoot badhte paani ke upar rehte hain;
• yeh root growth aur root-hair banne ko promote karti hai, jisse absorb karne wali surface badhti hai;
• yeh seed aur bud dormancy todti hai, jisse peanut seeds mein germination aur potato tubers mein sprouting shuru hoti hai;
• pineapple mein flowering shuru karne aur fruit set ko synchronise karne ke liye ise use kiya jaata hai, aur yeh mango mein flowering induce karti hai.

Kyunki yeh itne saare processes regulate karti hai, ethylene kisaanon ke sabse zyada use kiye jaane wale PGRs mein se hai. Woh gas ko khud shayad hi handle karte hain. Iski jagah woh ethephon spray karte hain, ek compound jo paani mein ghul jaata hai, jaldi absorb hokar plant mein failta hai, aur phir toot kar dheere-dheere ethylene chhodta hai. Yeh tomatoes aur apples ke pakne ko tez karta hai, cotton, cherry aur walnut ki fasal ko patla karne ke liye flowers aur fruits girata hai, aur female flowers ka hissa badhakar cucumber ki paidavaar badhata hai.

13.4.3.5 Abscisic acid

Jab leaf mein paani kam padne lagta hai, to abscisic acid uska alarm signal hai. ABA guard cells se stomata band karwata hai (Fig. 13.14) aur drought, thand aur doosre stresses ke liye plant ki tolerance badhata hai, isliye iska nickname stress hormone hai. Seeds mein yeh shuru se aakhir tak zaroori hai: yeh seed development aur maturation ko guide karta hai, phir dormancy laata hai, jisse seed sookhne ke baad bhi bacha rehta hai aur bure seasons mein intezaar kar sakta hai, aur yeh seed ko germinate hone se rokta hai. Zyada broadly, yeh growth aur metabolism ko dheema karta hai. Yeh aam taur par gibberellins ka virodh karta hai, isliye ise GA antagonist kaha jaata hai. Iska naam un roles, abscission aur dormancy, ki yaad dilata hai jinke liye yeh sabse pehle discover hua tha.

Plant ki life ki koi bhi stage akele ek regulator par nahi chhodi jaati. Kabhi do PGRs ek hi direction mein push karte hain (complementary ya synergistic action), kabhi ek doosre ke against kheenchte hain (antagonism), aur kabhi ek akela kaam karta hai. Dormancy, abscission, senescence aur apical dominance, har ek kai PGRs ke beech balance se tay hota hai (Table 13.4).

Lekin PGRs ko sahi nazariye se dekho. Har cell ke genes tay karte hain ki plant kya kar sakta hai, aur environment kaafi had tak tay karta hai ki woh asal mein kya karta hai; PGRs aksar beech ke messengers hote hain. Jaise, light aur temperature PGRs ke through seed germination, dormancy, plant movements, flowering aur vernalisation ko control karte hain.