Ch 13 covers plant growth — phases, kinetics, and differentiation — and the role of plant growth regulators (hormones) and environmental signals in plant development.
Growth phases: meristematic (active division), elongation (cell expansion), maturation (differentiation). Growth rate: arithmetic (constant addition) or geometric (exponential). Plant hormones: Auxins (indole-3-acetic acid — cell elongation, apical dominance, phototropism). Gibberellins (stem elongation, bolting, seed germination). Cytokinins (cell division, delay senescence). Ethylene (fruit ripening, leaf abscission). Abscisic acid/ABA (stress responses, stomatal closure, seed dormancy).
Photoperiodism: flowering response to relative lengths of light and dark periods. Short-day plants (SDP): flower when day length < critical (chrysanthemum). Long-day plants (LDP): flower when day length > critical (wheat). Day-neutral plants: not affected (tomato). Vernalisation: exposure to low temperature promotes earlier flowering in some plants (winter wheat). Phytochrome: light-sensitive pigment involved in photoperiodism.
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Apical dominance is the phenomenon where the growing apex (terminal bud) inhibits the growth of lateral (axillary) buds below it. This is caused by auxin produced in the apical meristem flowing downward. When the terminal bud is removed (pruning), lateral buds grow — this is why pruning makes plants bushier. Cytokinins promote lateral bud growth, opposing auxin.
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