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Plant Responses to Internal and External Stimuli; Bio notes for Chinaman.
Topic Started: Feb 25 2009, 06:59 PM (371 Views)
Danny Keen
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You'll have to bear with me, since this doesn't double-indent when making lists. Also, I italicized the stuff he told us was very important, and he wants us to know the comparisons and contrastisons between the hormones.

Plant Hormones


* Hormone: chemical signals for coordination
* Tropism: Moving towards or away from stimuli
Differs from taxis, since taxis entails moving the entire body.
- Gravitropism and thigmotropism
* Auxin
- Located in seed embryos, meristems of apical buds, young leaves
- Function: stem elongation, root growth, differentiation, budding, fruit budding, apical dominance, tropisms
* Cytokinins
- Zeatin
* In roots
* Root growth & differentiation, cell division & growth, germination, delay senescence (aging), apical dominance (w/ help from auxin)
* Giberellins
- GA3
* In meristems of apical buds & roots, young leaves, embryos
* Germination of seed & bud, stem elongation, leaf growth, flowering (bolting), fruit development, root growth & differentiation
* Abscesic acid (ABA)
- In leaves, stems, roots, green fruit
- Inhibits growth, closes stomata during stress, counteracts breaking of dormancy
- Facilitates maturation
* Ethylene
- Gaseous hormone
- In ripening fruit tissue, stem nodes, aging leaves & flowers
- Ripens fruit, opposes auxin (I can't really read my notes right here, and some of it doesn't make sense), involved in growth and development of roots, flowers, & leaves, role in senescence

Daily and Seasonal Responses


* Circadian rhythms (24-hour period)
* Photoperiodism (phytochromes)
* Short-day plant: light period shorter than critical length to flower, flowers in fall, winter, and late summer; poinsettia and chrysanthemum
* Long-day plant: light period longer than critical length to flower, flowers in spring and early summer; spinach, radish, lettuce, iris
* Day-neutral plant: unaffected by photoperiod (tomato, rice, dandelion)
* Critical night length controls flowering

Phytochromes


* Plant pigments measuring length of darkness in a photoperiod
- Pr: red absorbing (660 nm)
- Pfr: far red absorbing (730 nm)
* Red light shortens the dark period
* Far red negates the red light (I'm guessing it also lengthens the dark period or something, I dunno)


That's where we stopped.
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