Glossary: Key Terms — PP-03 — Notes

Term	Definition
Abscission	Shedding of leaves, fruits, or other organs from a plant; promoted by ethylene
Abscisic Acid (ABA)	Terpenoid plant hormone; the "stress hormone"; promotes stomatal closure and dormancy
Apical Dominance	Suppression of lateral bud growth by high auxin from the apical bud
Arithmetic Growth	Linear growth where only one daughter cell continues dividing; Lt = $L_{0}$ + rt
Auxin (IAA)	Indole compound plant hormone; promotes cell elongation, apical dominance, phototropism
Bolting	Rapid internodal elongation in rosette plants induced by gibberellin
Climacteric Fruit	Fruit that shows a burst of ethylene production during ripening (e.g., banana, mango)
Cytokinin	Adenine derivative hormone; promotes cell division; delays senescence
Day-Neutral Plant (DNP)	Plant that flowers regardless of photoperiod (e.g., tomato, cucumber)
Dedifferentiation	Loss of specialization by mature cells; return to meristematic activity
Differentiation	Permanent structural and functional specialization of cells
Ethylene	Only gaseous plant hormone ( $C_{2}H_{4}$ ); promotes fruit ripening, abscission
Florigen	The transmissible flowering signal produced in leaves; identified as FT protein
Geometric Growth	Exponential growth; both daughter cells divide; $W_{1}$ = $W_{0}$ eʳᵗ
Gibberellin ( $GA_{3}$ )	Terpenoid hormone; promotes stem elongation, dormancy breaking, alpha-amylase induction
Guard Cells	Paired cells surrounding stomata; regulate stomatal opening/closing
Lag Phase	First phase of sigmoid growth; slow preparation for cell division
Log Phase	Second phase of sigmoid growth; maximum exponential growth rate
Long-Day Plant (LDP)	Plant that flowers when day length exceeds critical photoperiod (e.g., wheat, spinach)
Parthenocarpy	Development of fruits without fertilization; induced by auxin or gibberellin
Pfr	Active form of phytochrome (far-red absorbing); promotes LDP flowering
Photoperiodism	Response of plants to relative duration of light and dark periods
Phytochrome	Photoreceptor protein that mediates photoperiodic responses; has Pr and Pfr forms
Pr	Inactive form of phytochrome (red light absorbing)
Redifferentiation	Dedifferentiated cells maturing again into permanent tissue
Richmond-Lang Effect	Delay of leaf senescence by cytokinins
Short-Day Plant (SDP)	Plant that flowers when night exceeds critical night length (e.g., rice, chrysanthemum)
Sigmoid Curve	S-shaped growth curve: lag → log → stationary phases
Stationary Phase	Third phase of sigmoid growth; growth near zero due to limiting factors
Totipotency	Capacity of a single cell to develop into a complete organism
Triple Response	Ethylene-induced response: inhibited elongation + radial swelling + horizontal growth
Vernalization	Cold treatment (0–5°C) to induce or accelerate flowering
2,4-D	Synthetic auxin used as selective herbicide; kills dicot weeds