4.9.12
Plants ek calendar nahi dekh sakte, phir bhi bahut se plants bilkul sahi season mein flower karte hain har saal. KAISE? Woh raat ki lambaai measure karte hain ek light-sensitive protein clock se. Flowering ka timing sahi hona life-or-death matter hai: bahut jaldi flower karo toh pollinators nahi hote ya frost maar deta hai; bahut der se flower karo toh seeds winter se pehle kabhi ripen nahi hote. Toh evolution ne plants ko ek tarika diya ki woh light se seasons padh sakein — ise photoperiodism
Definition PhotoperiodismPhotoperiodism ek organism ka physiological response hai din aur raat ki relative lengths (photoperiod) ke baare mein, jo flowering jaisi processes ko control karta hai.
Critical photoperiod woh day length threshold hai jiske upar ya neeche ek plant flowering ki taraf switch karta hai.
KYU matter karta hai? Yeh flowering ko season ke saath synchronise karta hai, taaki pollinators, favourable weather, aur seed set karne ka time mile.
Definition Plant flowering classes
Short-Day Plants (SDP): flower karte hain jab day length critical value se kam ho (yaani lambi raatein). Examples: chrysanthemum, rice, soybean, tobacco . Autumn/winter mein flower karte hain.Long-Day Plants (LDP): flower karte hain jab day length critical value se zyada ho (yaani choti raatein). Examples: wheat, spinach, radish, henbane . Spring/summer mein flower karte hain.Day-Neutral Plants (DNP): day length se independent hokar flower karte hain. Examples: tomato, cucumber, maize .
Common mistake "Short-day plants ko bahut zyada light chahiye — naam mein shortday likha hai!"
Kyun sahi lagta hai: day word se lagta hai plant daylight measure kar raha hai.
Sahi baat: jo actually matter karta hai woh hai uninterrupted DARK period (raat) ki lambaai . Ek short-day plant actually ek long-night plant hai. Classic proof: ek SDP ki lambi raat ko light ki ek chhoti flash (night break ) se interrupt karo aur woh flower NAHI karega — chahe total daylight unchanged raha ho. Iss ek experiment ne "day-length" waale idea ko khatam kar diya.
Pr red (660 nm) Pfr Pfr far-red (730 nm) Pr
HOW yeh time track karta hai:
Daylight mein (jo red se bhara hota hai), Pr convert hota hai Pfr mein → toh dusk tak leaf mein Pfr bhar jaata hai.Raat ke dauran, Pfr dheere dheere wapas Pr mein revert hota hai (dark reversion) aur degrade bhi hota hai.Dawn pe Pfr ki jo bachi hui maatra hoti hai woh encode karti hai raat kitni lambi thi . Lambi raat → bahut kam Pfr bacha; choti raat → bahut zyada Pfr bacha.
Intuition Leaf detect karta hai, bud act karta haiLeaf shoot apex (bud) par bante hain. Toh ek mobile signal ko leaf → bud tak travel karna padta hai.
Florigen flowering ka hormone-signal hai. Iska molecular identity FT (FLOWERING LOCUS T) genephloem ke through shoot apex tak transport hota hai, jahan yeh vegetative se floral growth mein switch trigger karta hai.
Signalling chain (pathway ko first principles se derive karna):
Sahi photoperiod → leaf mein correct phytochrome state.
Yeh CONSTANS (CO) protein ko regulate karta hai.
CO FT gene on karta hai → FT protein (florigen).
FT phloem se apex tak jaata hai, FD ke saath partner banata hai, aur floral identity genes (e.g. APETALA1 ) activate karta hai.
Apical meristem ek floral meristem ban jaata hai → flower banta hai.
Vernalisation prolonged cold ki period se flowering ka promotion hai. Yahi woh tarika hai jisse kuch plants (e.g. winter wheat) ensure karte hain ki woh spring mein flower karein winter ke baad , pehle nahi. Yeh photoperiodism se alag hai (temperature vs light) lekin dono aksar saath mein kaam karte hain.
Worked example Example 1 — Kya ek SDP flower karega?Ek chrysanthemum (SDP) ka critical photoperiod = 14 h. Use 10 h light, 14 h dark milta hai.
Step: Night length ko required minimum se compare karo. Yeh step kyun? SDP = long-night plant; sirf dark period matter karta hai.
Raat = 14 h. Kya yeh critical night (= 24 − 14 = 10 h) se zyada hai? Haan, 14 > 10. Flowers. ✔
Worked example Example 2 — Night breakSame plant, 10 h light / 14 h dark, lekin raat ke 7th hour par ek red flash .
Step: Flash 14 h raat ko do ~7 h halves mein tod deta hai. Yeh step kyun? Flowering ke liye ek continuous lambi raat chahiye. Red flash Pfr banata hai, clock reset karta hai.
Koi bhi single dark period ≥ 10 h nahi → Flower NAHI karta. ✘
Worked example Example 3 — Red phir far-redSDP ko mid-night mein red flash, phir far-red flash do.
Step: Far-red Pfr → Pr reverse karta hai, break undo karta hai. Yeh step kyun? Aakhri wavelength decide karti hai; final state "dark-night" Pr hai. → Plant phir se lambi raat dekhta hai. Flowers. ✔
Worked example Example 4 — LDP same treatment meinEk radish (LDP, critical photoperiod 12 h) ko 10 h light / 14 h dark milta hai red night break ke saath .
Step: LDP choti raatein chahta hai; night break use "choti raat" ka illusion deta hai. Yeh step kyun? Restored Pfr long-day conditions signal karta hai. → Flowers. ✔ (SDP se bilkul ulta response!)
Recall Feynman: ek 12-saal ke bachche ko samjhaoSocho ek plant ek chhota sa hourglass pakde hua hai jo sirf tab chalta hai jab andhera ho. Din mein sunlight hourglass ke upar ko ek khaas "day-sand" jise Pfr kehte hain se bhar deti hai. Raat ko sand dheere dheere trickle hoti jaati hai. Jab subah aati hai, plant feel karta hai kitni sand bachi hai: zyada sand = raat choti thi (garmi); almost koi sand nahi = raat lambi thi (sardi). Kuch plants flower karte hain jab raatein lambi hoti hain, kuch jab choti. Agar tum andar ghus ke raat ke beech mein ek flashlight jalaao, tum hourglass refill kar dete ho — aur confused plant sochta hai raat choti thi! Leaf yeh sab figure out karti hai, phir ek secret message (florigen/FT ) plant ki "straws" (phloem) se tip tak bhejti hai, use bolta hai: "Flower banane ka time aa gaya!"
Mnemonic Pigment directions yaad rakho"Red Runs it, Far-red Fixes(reverses) it." Aur: P fr = f inished, r eady (active) form.
Categories ke liye: S hort-D ay = S ays it needs D ark (lambi raat).
#flashcards/biology
Photoperiodism specifically kiska response hai? Din aur raat ki relative lengths (photoperiod) ka.
Flowering time karne ke liye plant actually kya measure karta hai — day length ya night length? Continuous dark (raat) period ki lambaai .
Critical photoperiod define karo. Woh threshold day length jiske upar/neeche ek plant flowering ki taraf switch karta hai.
Ek short-day plant flower karta hai jab din critical value se ___ hota hai. kam (yaani raatein lambi hoti hain).
Short-day plants ke do examples do. Chrysanthemum, rice, soybean, tobacco (koi bhi do).
Long-day plants ke do examples do. Wheat, spinach, radish, henbane (koi bhi do).
Day-neutral plant kya hota hai? Example? Day length se regardless flower karta hai; e.g. tomato, maize, cucumber.
Photoperiodism ke liye light-sensing pigment ka naam batao. Phytochrome.
Phytochrome ka kaun sa form active hai aur kaun sa wavelength use convert karta hai? Pfr (active), red ~660 nm light se banta hai.
Pfr ko wapas Pr mein kaun sa wavelength convert karta hai? Far-red ~730 nm.
"Night break" kya hota hai aur SDP par iska kya effect hota hai? Dark period ke dauran red-light ki flash; yeh SDP mein flowering rokta hai.
Red-then-far-red flash SDP mein flowering kyun restore karta hai? Far-red Pfr→Pr reverse karta hai; aakhri wavelength decide karti hai, toh plant phir lambi raat padhta hai.
Photoperiod kahan perceive hota hai aur flowers kahan bante hain? Leaf mein perceive hota hai; flowers shoot apex/bud par bante hain.
Florigen kya hai aur iska molecular identity kya hai? Mobile flowering signal; FT (FLOWERING LOCUS T) protein .
Florigen kaise travel karta hai? Phloem se leaf se shoot apex tak.
Vernalisation define karo. Cold ke prolonged exposure se flowering ka promotion.
Phytochrome and Photoreceptors Plant Hormones Vernalisation Phloem Transport (Translocation) Shoot Apical Meristem and Floral Development Circadian Rhythms in Plants Seed Germination and Light
