Plant Growth and Development

Beginner - Story ModeTopper - Revision

1. Growth - The Increase That You Can Measure

Imagine you mark a plant height daily with pencil on wall. That increase in length, weight, volume is growth. But in plants growth never stops at some parts - root tip, shoot tip keep dividing. That's indeterminate.

Growth has 3 phases like school life: Meristematic - small dense cytoplasm dividing like nursery kids. Elongation - vacuole grows cell wall loosens like teenager stretching height. Maturation - wall thickening differentiation like adult with job. Growth rate: Arithmetic 1,2,3 linear root elongating constant. Geometric 2,4,8,16 J-shaped but with limited food becomes S-shaped sigmoid. Formula Lt=Lo+rt for arithmetic, W1=Wo e^rt for geometric. AGR absolute growth, RGR growth per unit per time efficiency.

Part 1A - Growth Phases & Sigmoid Curve

Part 1B - Arithmetic vs Geometric AGR RGR Zoom

Revision: Growth irreversible increase indeterminate due to meristem. Phases meristematic elongation maturation. Arithmetic linear root, Geometric exponential S-curve. AGR absolute RGR relative.

2. Differentiation & Plasticity

Same baby cells but one becomes xylem pipe one becomes soft parenchyma. How? Differentiation - cells change structure to do specific work.

Dedifferentiation when mature cell forgets job and becomes meristem again like cork cambium from parenchyma interfascicular cambium. Redifferentiation that meristem again matures to secondary xylem. Plasticity same plant shows different leaf shapes due to environment. Cotton coriander larkspur heterophylly juvenile vs adult leaf different. Buttercup leaves in water vs air different. Shows development is flexible.

Part 2A - Differentiation Dediff Rediff Concept

Part 2B - Heterophylly Cotton Coriander Buttercup Zoom

Revision: Differentiation mature to specific Dediff mature to meristem Rediff meristem to mature. Plasticity different forms heterophylly cotton coriander buttercup.

3. Auxins - First Hormone

Darwin saw canary grass tip bends to light. Boysen-Jensen cut tip put mica bending stopped. Went isolated Auxin from coleoptile tip. IAA natural NAA 2,4-D synthetic.

Auxin is manager of top. High at shoot tip suppresses side buds apical dominance if you cut tip side branches grow bushy gardener prunes for bushy plant. Low auxin promotes rooting NAA used to grow roots from cuttings. High auxin kills dicot weeds 2,4-D herbicide. Auxin also makes seedless fruits parthenocarpy tomato prevents fruit and leaf drop.

Part 3A - Auxin Discovery Went Experiment

Part 3B - Apical Dominance Pruning & Herbicide Zoom

Revision: Auxin IAA Darwin Went. Functions apical dominance root initiation NAA parthenocarpy herbicide 2,4-D kills dicot prevents abscission.

4. Gibberellins & Cytokinins

Tall foolish rice seedlings by fungus Gibberella Kurosawa found GA. Bakanae disease. GA makes plants bolt. Cytokinin found from coconut milk Skoog Miller kinetin.

GA story Rosette cabbage stays flat GA makes it shoot up flowering bolting. GA makes malt in barley breaks starch to sugar. Sugarcane spray GA internodes elongate more sugar. Spray GA on grapes bigger size. Cytokinin is youth hormone promotes cell division delays leaf fall by keeping chlorophyll Richmond Lang effect. Cytokinin + Auxin ratio decides shoot vs root in tissue culture high CK shoots high auxin roots. GA and CK are growth pushers opposite ABA.

Part 4A - GA Bolting Amylase Sugarcane

Part 4B - Cytokinin Richmond Lang Delay Senescence Zoom

Revision: GA bolting rosette internode elongation sugarcane parthenocarpy malt breaking dormancy. Cytokinin kinetin zeatin cell division delay senescence Richmond Lang overcome apical dominance tissue culture.

5. Ethylene & ABA

One gas that ripens fruit Cousins found ethylene. One that closes everything in stress ABA. Both inhibitors but useful.

Ethylene triple response pea short stout stem radial swelling exaggerated hook helps seedling cross soil barrier. Ethylene promotes fruit ripening climacteric rise in respiration mango banana commercial ripening with ethephon. Also promotes leaf abscission flower senescence breaks seed dormancy peanut. ABA is stress hormone closes stomata in drought by K+ efflux guard cells flaccid induces seed dormancy prevents germination until favorable helps seeds tolerate desiccation. ABA antagonizes GA.

Part 5A - Ethylene Triple Response & Ripening

Part 5B - ABA Stomatal Closure & Dormancy Zoom

Revision: Ethylene gas C2H4 triple response pea ripening climacteric abscission senescence breaks dormancy. ABA stress stomatal closure drought seed dormancy desiccation tolerance antagonizes GA.

6. PGRs Overview Table

Don't memorize random remember pattern Auxin GA CK growth promoters ABA inhibitor Ethylene both. They talk to each other.

Auxin + CK tissue culture GA + ABA opposite dormancy vs germination ABA + Ethylene both promote abscission Auxin + Ethylene opposite rooting vs ripening. Apical dominance auxin suppresses CK promotes lateral. Senescence delayed by CK Auxin promoted by ABA Ethylene. For exam remember discovery Auxin Went GA Kurosawa CK Skoog Ethylene Cousins ABA Addicott.

Part 6A - PGRs Discovery & Functions Table

Part 6B - Hormone Interactions Synergy Antagonism Zoom

Revision: Growth promoters Auxin GA CK Inhibitor ABA Ethylene both. Discovery Auxin Went GA Kurosawa CK Skoog Miller Ethylene Cousins ABA Addicott.

7. Photoperiodism & Vernalization

Why chrysanthemum flowers in winter spinach in summer? Plant sees day length. Why wheat needs winter cold to flower? Vernalization.

Photoperiodism Leaf perceives light dark via phytochrome Pr Pfr makes florigen FT protein travels via phloem to shoot apical meristem converts to flower. SDP short day less than critical day length Chrysanthemum Soybean Poinsettia flowers when nights long. LDP long day more than 14h light Spinach Lettuce Wheat Radish flowers when days long. DNP day neutral Tomato Cucumber flowers anytime. Vernalization Some plants need low temp 0-5C winter to flower winter wheat sown in winter if sown in spring no flower. Cold suppresses FLC repressor activates florigen. Reduces vegetative phase early flowering.

Part 7A - Photoperiodism SDP LDP DNP Types

Part 7B - Vernalization FLC Silencing & FT Florigen Zoom

Revision: Photoperiodism day length sensing leaf phytochrome florigen FT phloem to SAM. SDP short day long night Chrysanthemum LDP long day Spinach Wheat DNP Tomato. Vernalization cold 0-5C promotes flowering suppresses FLC winter wheat.