University:
Meredith College
Course:
BIO-211 | Plant Biology
Academic year:

2024
Views:

47

Pages:

2
Author:

Amy TGT

4/16/24 Plant Hormones & Tropisms 1. Auxins – produced in apical meristems, buds, young leaves & actively growing parts of plants – Triggers the production of other plant hormones – Promotes cell enlargement & stem growth – Promotes fruit development – Inhibit lateral branching 2. Cytokinins – Cell enlargement – Differentiation of tissues – Development of chloroplasts – Stimulation of cotyledon growth – Delays aging in leaves – Also used to clone plants 3. Gibberellins (GA) – Speeds up growth rate of dicots (& some monocots) – Dwarf plants have low gibberellins 4. Ethylene – Ripens fruit o Promotes sugar production o Turns on genes for carotenoid synthesis (changes fruit color) – Released to encourage neighbor fruit ripening – Promotes leaf abscission 5. Abscisic acid (ABA) – Prevents seeds from germinating while still on plant – Helps leaves respond to excessive water loss External factors affecting plants growth – – – – Temperature Light Day length Gravity Hormones – production dictated by genes Plant growth response results from signal transduction pathway Cells communicate with each other via hormones Strawberry = aggregate fruit – The little seeds on the surface of the strawberry – each represents an ovary – The part we eat is the receptacle Tropisms Phototropism – growth toward light – – – – Greater cell elongation on shaded side Less stem growth on light side Positive phototropism: growth towards light (shoots) Negative phototropism: away from light (roots: either insensitive to light or actively grow away from it) Gravitropism – why do roots grow downward & stems grow upward? – – Gravity may be perceived by amyloplasts (starch-storing plastids) in the root cap Roots are positively gravitropic Hydrotropism – growth of roots in response to a moisture gradient Thigmotropism – response to touch – Vine tendril growth Photoperiodism – – – Short-day plants Long-day plants Day-neutral plants Dormancy – – Seeds o Require specific cues from the environment (water, light, abrasion) Buds Heliotropism